WEBVTT 00:00:00.000 --> 00:00:02.400 align:middle line:90% [SQUEAKING] 00:00:02.400 --> 00:00:04.320 align:middle line:90% [RUSTLING] 00:00:04.320 --> 00:00:10.080 align:middle line:90% [CLICKING] 00:00:10.080 --> 00:00:12.200 align:middle line:84% PROFESSOR: So we're very fortunate today 00:00:12.200 --> 00:00:15.470 align:middle line:84% to have Dr. Maria Gatu Johnson join us to give a guest lecture 00:00:15.470 --> 00:00:17.150 align:middle line:90% on neutron diagnostics. 00:00:17.150 --> 00:00:21.170 align:middle line:84% Maria is a principal research scientist at the PSFC. 00:00:21.170 --> 00:00:23.810 align:middle line:84% She did her PhD working on neutron spectroscopy 00:00:23.810 --> 00:00:26.150 align:middle line:90% on jet, on magnetic confinement. 00:00:26.150 --> 00:00:29.100 align:middle line:84% But now she works on inertial confinement fusion. 00:00:29.100 --> 00:00:32.390 align:middle line:84% And in particular, her work on the magnetic recoil spectrometer 00:00:32.390 --> 00:00:36.350 align:middle line:84% on NIF was a key to understanding the record neutron 00:00:36.350 --> 00:00:39.230 align:middle line:84% yield that we got last year in the ignition shots. 00:00:39.230 --> 00:00:42.170 align:middle line:84% So we're very fortunate to have Maria here, and looking forward 00:00:42.170 --> 00:00:43.298 align:middle line:90% to hearing her talk. 00:00:43.298 --> 00:00:44.840 align:middle line:84% MARIA GATU JOHNSON: OK, thanks, Jack. 00:00:44.840 --> 00:00:49.220 align:middle line:84% So an hour and a half on nuclear diagnostics. 00:00:49.220 --> 00:00:52.100 align:middle line:84% For ICF, that's kind of a lot to squeeze in. 00:00:52.100 --> 00:00:54.320 align:middle line:90% So I did a bit of a sampling. 00:00:54.320 --> 00:00:57.500 align:middle line:84% I want you guys to ask questions as we go through. 00:00:57.500 --> 00:00:59.750 align:middle line:84% If there's anything you're particularly interested in, 00:00:59.750 --> 00:01:02.870 align:middle line:84% stop me and we'll talk a little bit more about it, 00:01:02.870 --> 00:01:06.320 align:middle line:90% try to touch on the key things. 00:01:06.320 --> 00:01:08.540 align:middle line:84% Also, there's a lot of familiar faces today. 00:01:08.540 --> 00:01:10.830 align:middle line:84% So a lot of you know details of what 00:01:10.830 --> 00:01:14.070 align:middle line:84% we'll be talking about today, in some cases, better than I do. 00:01:14.070 --> 00:01:16.210 align:middle line:84% So then feel free to chime in as well. 00:01:16.210 --> 00:01:19.030 align:middle line:90% So with that, we'll get started. 00:01:19.030 --> 00:01:20.550 align:middle line:84% So yeah, as Jack said, we're going 00:01:20.550 --> 00:01:26.420 align:middle line:84% to be talking about nuclear diagnostics for ICF plasmas. 00:01:26.420 --> 00:01:28.850 align:middle line:84% This, in particular, illustrates three facilities 00:01:28.850 --> 00:01:30.620 align:middle line:90% where we do ICF work-- 00:01:30.620 --> 00:01:33.590 align:middle line:84% the National Ignition Facility in Livermore in California, 00:01:33.590 --> 00:01:37.170 align:middle line:84% the Z facility at Sandia National Labs in Albuquerque, 00:01:37.170 --> 00:01:40.910 align:middle line:84% New Mexico, and the OMEGA laser in Rochester, upstate New York. 00:01:40.910 --> 00:01:43.130 align:middle line:84% And this is actually a picture of the instrument 00:01:43.130 --> 00:01:45.290 align:middle line:84% that Jack just talked about in his introduction, 00:01:45.290 --> 00:01:48.230 align:middle line:84% the magnetic recoil neutron spectrometer installed 00:01:48.230 --> 00:01:50.120 align:middle line:84% on the NIF target chamber, which is 00:01:50.120 --> 00:01:54.590 align:middle line:84% the blue, circular, spherical part that you can see there 00:01:54.590 --> 00:01:56.060 align:middle line:90% in the background. 00:01:56.060 --> 00:01:58.640 align:middle line:84% But I thought, as part of this, we'll touch a little bit 00:01:58.640 --> 00:02:01.310 align:middle line:84% on-- if I can get this to move forward-- 00:02:01.310 --> 00:02:04.730 align:middle line:84% some comparisons to diagnostics for magnetic confinement fusion 00:02:04.730 --> 00:02:05.820 align:middle line:90% as well. 00:02:05.820 --> 00:02:08.030 align:middle line:84% So these pictures here, that's the inside of the jet 00:02:08.030 --> 00:02:10.280 align:middle line:84% [INAUDIBLE] time of flight neutron 00:02:10.280 --> 00:02:12.620 align:middle line:84% spectrometer at the [INAUDIBLE] which I 00:02:12.620 --> 00:02:14.902 align:middle line:90% did build for my graduate work. 00:02:14.902 --> 00:02:16.610 align:middle line:84% So we'll talk about that one a little bit 00:02:16.610 --> 00:02:20.390 align:middle line:84% as well when we get to that point. 00:02:20.390 --> 00:02:23.900 align:middle line:84% Brief outline-- find this a little weird 00:02:23.900 --> 00:02:28.680 align:middle line:84% between switching the computer and being behind the camera. 00:02:28.680 --> 00:02:31.380 align:middle line:84% We'll start by talking about implosion parameters 00:02:31.380 --> 00:02:32.370 align:middle line:90% and nuclear signatures. 00:02:32.370 --> 00:02:35.220 align:middle line:84% What are we actually looking for in the ICF implosions? 00:02:35.220 --> 00:02:38.100 align:middle line:84% What do we get from the nuclear diagnostics? 00:02:38.100 --> 00:02:40.543 align:middle line:84% So that's kind of the broad overview background. 00:02:40.543 --> 00:02:42.960 align:middle line:84% And then we'll go into a little bit more technical stuff-- 00:02:42.960 --> 00:02:44.940 align:middle line:84% the nuclear diagnostics that we use. 00:02:44.940 --> 00:02:48.630 align:middle line:84% And I've divided it into neutron activation, neutron 00:02:48.630 --> 00:02:52.890 align:middle line:84% spectrometry, neutron imaging, charged-particle spectrometry, 00:02:52.890 --> 00:02:55.620 align:middle line:84% touching a little bit on other charged-particle magnets as 00:02:55.620 --> 00:02:59.070 align:middle line:84% well, and then finally, reaction-rate history. 00:02:59.070 --> 00:03:00.510 align:middle line:84% And finally, if we have time, I'll 00:03:00.510 --> 00:03:03.060 align:middle line:84% just spend a few slides discussing 00:03:03.060 --> 00:03:04.560 align:middle line:84% the impact of nuclear measurements 00:03:04.560 --> 00:03:07.410 align:middle line:84% on the ICF program that is in particular. 00:03:07.410 --> 00:03:10.140 align:middle line:90% 00:03:10.140 --> 00:03:13.070 align:middle line:84% So let's start with the implosion parameters 00:03:13.070 --> 00:03:14.850 align:middle line:90% and nuclear signatures. 00:03:14.850 --> 00:03:17.960 align:middle line:84% So the nuclear emission from an ICF experiment 00:03:17.960 --> 00:03:21.170 align:middle line:84% carries information about the state of the fusion fuel. 00:03:21.170 --> 00:03:23.180 align:middle line:84% And this is actually what really excites 00:03:23.180 --> 00:03:26.540 align:middle line:84% me about nuclear diagnostics is that they carry information 00:03:26.540 --> 00:03:31.440 align:middle line:84% directly about what's happening in their reactions. 00:03:31.440 --> 00:03:33.280 align:middle line:84% They're the products of the reaction. 00:03:33.280 --> 00:03:35.907 align:middle line:84% So they know exactly what's going on. 00:03:35.907 --> 00:03:37.740 align:middle line:84% We can count the number of nuclear products, 00:03:37.740 --> 00:03:40.320 align:middle line:84% and that gives us a measure of the number of fusion reactions 00:03:40.320 --> 00:03:41.640 align:middle line:90% that happen. 00:03:41.640 --> 00:03:44.040 align:middle line:84% We can look at the energy spread of the fusion products, 00:03:44.040 --> 00:03:47.220 align:middle line:84% and that gives us a measure of the plasma ion temperature. 00:03:47.220 --> 00:03:49.795 align:middle line:84% We can look at the energy upshift of the fusion products 00:03:49.795 --> 00:03:52.020 align:middle line:90% to fuel velocity. 00:03:52.020 --> 00:03:54.120 align:middle line:90% Was there a comment online? 00:03:54.120 --> 00:03:56.730 align:middle line:90% Can you guys hear me OK? 00:03:56.730 --> 00:03:58.490 align:middle line:84% AUDIENCE: We can hear you great, thanks. 00:03:58.490 --> 00:03:59.950 align:middle line:90% MARIA GATU JOHNSON: Great. 00:03:59.950 --> 00:04:02.770 align:middle line:84% And we can look at a scatter or downshift 00:04:02.770 --> 00:04:06.715 align:middle line:84% of the nuclear products to study area 00:04:06.715 --> 00:04:08.980 align:middle line:84% of density, which I'll discuss what that is, 00:04:08.980 --> 00:04:11.500 align:middle line:84% of the compressed fuel and shell. 00:04:11.500 --> 00:04:13.750 align:middle line:84% We can also take an image of the nuclear emission 00:04:13.750 --> 00:04:16.149 align:middle line:84% to study the spatial burn profile, 00:04:16.149 --> 00:04:18.550 align:middle line:84% and we can look at the temporal evolution 00:04:18.550 --> 00:04:21.250 align:middle line:84% to determine how nuclear burn evolves in time. 00:04:21.250 --> 00:04:23.620 align:middle line:84% And actually, if you look at this, quite a few of these 00:04:23.620 --> 00:04:27.070 align:middle line:84% are also relevant for magnetic confinement fusion. 00:04:27.070 --> 00:04:29.470 align:middle line:84% We can obtain similar information 00:04:29.470 --> 00:04:32.620 align:middle line:84% by looking at the nuclear emission from a tokamak, 00:04:32.620 --> 00:04:33.980 align:middle line:90% for example. 00:04:33.980 --> 00:04:36.760 align:middle line:84% The exception is the area of density, which 00:04:36.760 --> 00:04:39.730 align:middle line:90% is a specific quantity to ICF. 00:04:39.730 --> 00:04:42.070 align:middle line:84% So I want to spend a few slides talking 00:04:42.070 --> 00:04:45.260 align:middle line:90% about why that's important. 00:04:45.260 --> 00:04:47.120 align:middle line:84% As I think all of you know already, 00:04:47.120 --> 00:04:49.790 align:middle line:84% ICF uses the inertia of a dense shell 00:04:49.790 --> 00:04:53.060 align:middle line:84% to confine the plasma before it blows apart 00:04:53.060 --> 00:04:55.940 align:middle line:90% under its own pressure. 00:04:55.940 --> 00:05:01.010 align:middle line:84% We can express a confinement time in terms of the sounds, cs 00:05:01.010 --> 00:05:01.670 align:middle line:90% here. 00:05:01.670 --> 00:05:04.040 align:middle line:84% This is kind of illustration of how it works. 00:05:04.040 --> 00:05:06.590 align:middle line:90% And if we take a-- 00:05:06.590 --> 00:05:07.423 align:middle line:90% [INTERPOSING VOICES] 00:05:07.423 --> 00:05:09.048 align:middle line:84% AUDIENCE: Should I turn this one round? 00:05:09.048 --> 00:05:11.660 align:middle line:84% And then you've got one fewer computer to look at. 00:05:11.660 --> 00:05:14.690 align:middle line:84% MARIA GATU JOHNSON: Trying to switch slides here. 00:05:14.690 --> 00:05:16.160 align:middle line:90% OK, that's good. 00:05:16.160 --> 00:05:17.183 align:middle line:90% AUDIENCE: There we go. 00:05:17.183 --> 00:05:19.100 align:middle line:84% MARIA GATU JOHNSON: We can take a mass average 00:05:19.100 --> 00:05:21.510 align:middle line:90% of the local confinement time. 00:05:21.510 --> 00:05:27.320 align:middle line:84% And that gives us the confinement time as the radius 00:05:27.320 --> 00:05:32.390 align:middle line:84% over the sound speed with a 1/4 of r to the 4 in that. 00:05:32.390 --> 00:05:34.940 align:middle line:84% So I'm not going to go through that integral in detail, 00:05:34.940 --> 00:05:38.200 align:middle line:90% but it's a very simple one. 00:05:38.200 --> 00:05:42.710 align:middle line:84% Yeah, so this is the confinement time. 00:05:42.710 --> 00:05:47.840 align:middle line:84% OK, so then if we look at the standard, number density times 00:05:47.840 --> 00:05:50.180 align:middle line:84% confinement, and plug this expression 00:05:50.180 --> 00:05:55.200 align:middle line:84% from the previous slide in for the confinement time, 00:05:55.200 --> 00:05:57.950 align:middle line:90% it gives us this expression. 00:05:57.950 --> 00:06:02.050 align:middle line:84% So we see that number density times confinement time 00:06:02.050 --> 00:06:04.150 align:middle line:84% is a direct function of [INAUDIBLE], which 00:06:04.150 --> 00:06:06.560 align:middle line:84% is this area of density that we keep talking about, 00:06:06.560 --> 00:06:09.460 align:middle line:84% which is essentially a confinement parameter 00:06:09.460 --> 00:06:11.810 align:middle line:90% in inertial confinement fusion. 00:06:11.810 --> 00:06:15.310 align:middle line:84% And that's why we care about it so much. 00:06:15.310 --> 00:06:17.980 align:middle line:84% Oh yeah, even highlighting it there. 00:06:17.980 --> 00:06:21.460 align:middle line:84% High areal density-- or rho R, which 00:06:21.460 --> 00:06:23.860 align:middle line:84% you should refer to it as-- is required 00:06:23.860 --> 00:06:26.800 align:middle line:84% for a significant fraction of the fuel 00:06:26.800 --> 00:06:30.430 align:middle line:84% to burn before it disassembles under its own pressure. 00:06:30.430 --> 00:06:34.720 align:middle line:84% We can express the burn fraction, fb, 00:06:34.720 --> 00:06:39.100 align:middle line:84% as rho R divided by rho R times 6 grams per centimeter squared. 00:06:39.100 --> 00:06:40.667 align:middle line:84% That's at an ion temperature of 30 K. 00:06:40.667 --> 00:06:43.000 align:middle line:84% You can derive it at different [INAUDIBLE] temperatures. 00:06:43.000 --> 00:06:46.510 align:middle line:84% So that's kind of high compared to what we usually operate at. 00:06:46.510 --> 00:06:49.060 align:middle line:84% And this expression actually is derived 00:06:49.060 --> 00:06:52.660 align:middle line:84% from the fusion burn rate integrated over the confinement 00:06:52.660 --> 00:06:53.770 align:middle line:90% time. 00:06:53.770 --> 00:06:55.460 align:middle line:84% If we throw in some numbers on this, 00:06:55.460 --> 00:06:58.330 align:middle line:84% we can throw in that we want a burnup 00:06:58.330 --> 00:07:02.120 align:middle line:84% fraction of 25%, which really would be required for high gain. 00:07:02.120 --> 00:07:05.320 align:middle line:84% That means we need a rho R of 2 grams per centimeter squared. 00:07:05.320 --> 00:07:07.490 align:middle line:84% OK, just to put this in perspective, 00:07:07.490 --> 00:07:09.880 align:middle line:84% the best performing NIF implosions to date 00:07:09.880 --> 00:07:12.580 align:middle line:84% have had a burnup fraction of about 5%. 00:07:12.580 --> 00:07:15.640 align:middle line:84% So this is really high performance. 00:07:15.640 --> 00:07:18.460 align:middle line:84% And then if we assume solid D-T, D-T ice 00:07:18.460 --> 00:07:23.200 align:middle line:84% has a density of 0.25 grams per cubic centimeters. 00:07:23.200 --> 00:07:28.060 align:middle line:84% Then we find that for ignition, we need a fuel mass about 1/2 00:07:28.060 --> 00:07:29.080 align:middle line:90% a kilogram. 00:07:29.080 --> 00:07:33.970 align:middle line:84% Again, this is with this expression, solid D-T ice. 00:07:33.970 --> 00:07:37.540 align:middle line:84% So then the question is, as I'm sure you've seen this 1,000 00:07:37.540 --> 00:07:39.190 align:middle line:84% times before in ICF presentations, 00:07:39.190 --> 00:07:42.120 align:middle line:84% can we really work with 0.5 kilograms of D-T fuel 00:07:42.120 --> 00:07:44.260 align:middle line:90% in a laboratory? 00:07:44.260 --> 00:07:46.090 align:middle line:90% Of course, the answer is no. 00:07:46.090 --> 00:07:48.250 align:middle line:84% That gives us a little too much yield, which 00:07:48.250 --> 00:07:50.860 align:middle line:90% is not quite what we want. 00:07:50.860 --> 00:07:53.980 align:middle line:84% And that motivates-- that in order 00:07:53.980 --> 00:07:57.190 align:middle line:84% to achieve the required areal density, our confinement 00:07:57.190 --> 00:08:00.160 align:middle line:84% parameter, i temperature and confinement time 00:08:00.160 --> 00:08:04.650 align:middle line:84% without destroying the lab, we need to compress the capsule. 00:08:04.650 --> 00:08:06.600 align:middle line:84% We actually have to compress it quite a lot. 00:08:06.600 --> 00:08:12.820 align:middle line:84% We get these rough parameters, starting from about a 2 00:08:12.820 --> 00:08:15.060 align:middle line:90% millimeter size capsule. 00:08:15.060 --> 00:08:18.570 align:middle line:84% Get down the radius of 30 to 50 microns, 00:08:18.570 --> 00:08:22.530 align:middle line:84% density like 700 grams per cubic centimeters from the 0.25 00:08:22.530 --> 00:08:23.970 align:middle line:90% that we started with. 00:08:23.970 --> 00:08:27.217 align:middle line:84% And an areal density of 2 grams per centimeter 00:08:27.217 --> 00:08:29.850 align:middle line:84% squared, temperatures from 5 to 40 keV, 00:08:29.850 --> 00:08:33.190 align:middle line:84% and confinement times from about 20 to 200 picoseconds. 00:08:33.190 --> 00:08:37.549 align:middle line:84% So looking at these numbers, these inclusion parameters 00:08:37.549 --> 00:08:40.700 align:middle line:84% really set the requirements on the different measurements. 00:08:40.700 --> 00:08:43.190 align:middle line:84% Typically, we want to achieve a 5% to 10% 00:08:43.190 --> 00:08:45.510 align:middle line:84% accuracy on these kinds of numbers. 00:08:45.510 --> 00:08:47.213 align:middle line:84% So that really tells you how well 00:08:47.213 --> 00:08:49.130 align:middle line:84% we need to be able to make these measurements. 00:08:49.130 --> 00:08:53.522 align:middle line:90% 00:08:53.522 --> 00:08:55.480 align:middle line:84% OK, so then we have a lot of different products 00:08:55.480 --> 00:08:57.310 align:middle line:90% that we can work with. 00:08:57.310 --> 00:09:00.040 align:middle line:84% And they really carry a wealth of information 00:09:00.040 --> 00:09:02.110 align:middle line:90% about ICF implosions. 00:09:02.110 --> 00:09:05.800 align:middle line:84% First of all, we have our primary products. 00:09:05.800 --> 00:09:07.900 align:middle line:84% All of you know that we primarily 00:09:07.900 --> 00:09:09.640 align:middle line:84% work with the D-T reaction, which 00:09:09.640 --> 00:09:15.256 align:middle line:84% gives us the alpha particle and the neutron [INAUDIBLE]. 00:09:15.256 --> 00:09:17.200 align:middle line:84% PROFESSOR: I don't think so unfortunately. 00:09:17.200 --> 00:09:18.790 align:middle line:84% MARIA GATU JOHNSON: OK, keep jumping. 00:09:18.790 --> 00:09:20.230 align:middle line:90% PROFESSOR: Yeah, sorry. 00:09:20.230 --> 00:09:21.670 align:middle line:84% MARIA GATU JOHNSON: You could use a board eraser, 00:09:21.670 --> 00:09:23.920 align:middle line:84% but that's only going to give you an extra foot or so. 00:09:23.920 --> 00:09:25.180 align:middle line:90% So it's probably not worth. 00:09:25.180 --> 00:09:28.090 align:middle line:84% MARIA GATU JOHNSON: OK, so that's 00:09:28.090 --> 00:09:30.370 align:middle line:90% the primary one we work with. 00:09:30.370 --> 00:09:32.680 align:middle line:84% If you look over here, that gives us 00:09:32.680 --> 00:09:35.260 align:middle line:84% the yield, the ion temperature, the areal density. 00:09:35.260 --> 00:09:37.870 align:middle line:84% We can also use it for yield versus time 00:09:37.870 --> 00:09:42.940 align:middle line:84% and use it to infer the confinement time and the radius 00:09:42.940 --> 00:09:44.290 align:middle line:90% of the capsule. 00:09:44.290 --> 00:09:46.030 align:middle line:84% There's also another branch, which 00:09:46.030 --> 00:09:48.680 align:middle line:84% gives us a gamma particle, which is actually quite useful. 00:09:48.680 --> 00:09:52.210 align:middle line:84% And we'll look a little bit at that as well later in the class. 00:09:52.210 --> 00:09:55.330 align:middle line:84% In addition to D-T, we can also look at primary products 00:09:55.330 --> 00:09:57.230 align:middle line:90% from the D-D reactions. 00:09:57.230 --> 00:09:59.900 align:middle line:84% We have two, one that gives a [INAUDIBLE] proton, 00:09:59.900 --> 00:10:02.720 align:middle line:84% one that gives a helium 3 and neutron. 00:10:02.720 --> 00:10:04.700 align:middle line:90% And actually, a lot of-- 00:10:04.700 --> 00:10:07.190 align:middle line:84% many confinement experiments have been working primarily 00:10:07.190 --> 00:10:08.330 align:middle line:90% with D-D to date. 00:10:08.330 --> 00:10:12.330 align:middle line:84% So you can use that neutron for a lot of measurements as well. 00:10:12.330 --> 00:10:14.150 align:middle line:84% And then the helium 3, we also work 00:10:14.150 --> 00:10:16.250 align:middle line:84% with in a lot of surrogate experiments 00:10:16.250 --> 00:10:19.500 align:middle line:84% where we don't want to do D-T and it's a different thing. 00:10:19.500 --> 00:10:21.890 align:middle line:84% And then actually, it's quite similar to D-T. We also 00:10:21.890 --> 00:10:25.220 align:middle line:84% get alpha particle, get a proton instead of a neutron with pretty 00:10:25.220 --> 00:10:27.050 align:middle line:90% high energy. 00:10:27.050 --> 00:10:29.207 align:middle line:90% OK, so those are the primaries. 00:10:29.207 --> 00:10:31.040 align:middle line:84% Counting the number of primaries to generate 00:10:31.040 --> 00:10:32.870 align:middle line:84% gives us a direct measurement of how many 00:10:32.870 --> 00:10:34.490 align:middle line:84% fusion reactions we had, obviously. 00:10:34.490 --> 00:10:39.230 align:middle line:84% So that's a quick way of getting the yield for inflation. 00:10:39.230 --> 00:10:43.080 align:middle line:84% Not necessarily always easy, but basically that's how it works. 00:10:43.080 --> 00:10:45.770 align:middle line:84% We can also have secondary products, which I actually won't 00:10:45.770 --> 00:10:47.190 align:middle line:90% be spending much time on today. 00:10:47.190 --> 00:10:48.870 align:middle line:84% But if you're interested in that, 00:10:48.870 --> 00:10:50.850 align:middle line:84% I'm happy to answer questions afterwards. 00:10:50.850 --> 00:10:53.540 align:middle line:84% So that's when one of the fast products produced 00:10:53.540 --> 00:10:57.940 align:middle line:84% in a primary reaction goes on to react with a thermal fuel 00:10:57.940 --> 00:11:01.390 align:middle line:84% and to give a broader energy spectrum of the reaction 00:11:01.390 --> 00:11:02.960 align:middle line:90% products. 00:11:02.960 --> 00:11:05.180 align:middle line:84% And then we have knock-on reactions. 00:11:05.180 --> 00:11:08.010 align:middle line:84% We'll spend a little bit of time looking at how this works. 00:11:08.010 --> 00:11:14.260 align:middle line:84% So that's when the fast neutrons born in the D-T reaction 00:11:14.260 --> 00:11:18.610 align:middle line:84% hit one of the fuel ions to give faster fuel ion 00:11:18.610 --> 00:11:20.440 align:middle line:90% and a scattered neutron. 00:11:20.440 --> 00:11:23.510 align:middle line:84% We actually use this quite a lot. 00:11:23.510 --> 00:11:25.250 align:middle line:84% And we can also have similar reactions 00:11:25.250 --> 00:11:29.150 align:middle line:84% for the alpha particles scatter on the fuel ion 00:11:29.150 --> 00:11:31.670 align:middle line:90% and give [INAUDIBLE] fuel ions. 00:11:31.670 --> 00:11:33.440 align:middle line:84% I won't spend much time on this today, 00:11:33.440 --> 00:11:35.150 align:middle line:84% but this is the signature that they 00:11:35.150 --> 00:11:39.740 align:middle line:84% can use to look at what the alpha particles are doing 00:11:39.740 --> 00:11:44.030 align:middle line:84% in the plasma, in particular, when these fast neutrons react 00:11:44.030 --> 00:11:47.335 align:middle line:84% again, in a tertiary reaction, which 00:11:47.335 --> 00:11:49.415 align:middle line:84% I think the example's in here-- yeah, 00:11:49.415 --> 00:11:51.440 align:middle line:84% to give these fast neutrons, which we 00:11:51.440 --> 00:11:54.680 align:middle line:90% call alpha knock-on neutrons. 00:11:54.680 --> 00:11:59.030 align:middle line:84% Think some of you have heard about that before. 00:11:59.030 --> 00:12:04.710 align:middle line:84% OK, yeah, so this is actually pretty cool, 00:12:04.710 --> 00:12:10.120 align:middle line:84% these knock-on reactions are the easiest way of measuring rho R. 00:12:10.120 --> 00:12:12.720 align:middle line:84% So we look at some examples of that as we go through. 00:12:12.720 --> 00:12:15.870 align:middle line:90% 00:12:15.870 --> 00:12:18.300 align:middle line:84% OK, we already talked about this-- 00:12:18.300 --> 00:12:20.460 align:middle line:84% counting the number of emitted primary fusion 00:12:20.460 --> 00:12:21.705 align:middle line:90% products in a set. 00:12:21.705 --> 00:12:24.380 align:middle line:90% 00:12:24.380 --> 00:12:26.720 align:middle line:84% Solid angle and scaling it up to 4 pi 00:12:26.720 --> 00:12:28.680 align:middle line:84% gives us a measure of the total yield. 00:12:28.680 --> 00:12:33.340 align:middle line:84% So this is basically the yield reaction. 00:12:33.340 --> 00:12:35.040 align:middle line:84% I forgot to put the y in front of it. 00:12:35.040 --> 00:12:38.360 align:middle line:84% But if you do the integral over volume and time, 00:12:38.360 --> 00:12:41.227 align:middle line:90% the densities of the reactants-- 00:12:41.227 --> 00:12:43.310 align:middle line:84% typically, it could be [INAUDIBLE] and [INAUDIBLE] 00:12:43.310 --> 00:12:44.480 align:middle line:90% for D-T plasma-- 00:12:44.480 --> 00:12:48.170 align:middle line:84% and the reactivity-- and this is just a Kronecker delta. 00:12:48.170 --> 00:12:53.150 align:middle line:84% So if it's 2D, you get a factor of 1/2. 00:12:53.150 --> 00:12:55.280 align:middle line:90% That gives you the [INAUDIBLE]. 00:12:55.280 --> 00:12:57.350 align:middle line:84% And the reactivity is the integral 00:12:57.350 --> 00:13:00.350 align:middle line:84% over the reactants of the fuel ion distributions, 00:13:00.350 --> 00:13:02.400 align:middle line:90% the cross section. 00:13:02.400 --> 00:13:04.523 align:middle line:90% And then you can get-- 00:13:04.523 --> 00:13:05.690 align:middle line:90% this is actually an example. 00:13:05.690 --> 00:13:09.920 align:middle line:84% Reactivity is calculated according to that formula. 00:13:09.920 --> 00:13:12.680 align:middle line:84% That's written up in this paper, which 00:13:12.680 --> 00:13:14.630 align:middle line:84% if you haven't seen this paper before, 00:13:14.630 --> 00:13:18.410 align:middle line:84% this is really a key reference to go to if you want to look 00:13:18.410 --> 00:13:20.990 align:middle line:90% at how likely a reaction is. 00:13:20.990 --> 00:13:22.910 align:middle line:84% Obviously, the key is the most probable. 00:13:22.910 --> 00:13:24.660 align:middle line:90% Then we have the 2D reactions. 00:13:24.660 --> 00:13:26.020 align:middle line:90% We have a probability. 00:13:26.020 --> 00:13:28.140 align:middle line:84% And you can go to lower probability, [INAUDIBLE]. 00:13:28.140 --> 00:13:32.940 align:middle line:90% 00:13:32.940 --> 00:13:34.570 align:middle line:90% OK, yes. 00:13:34.570 --> 00:13:36.245 align:middle line:90% Go ahead, John. 00:13:36.245 --> 00:13:37.870 align:middle line:84% AUDIENCE: How do you deal with the fact 00:13:37.870 --> 00:13:39.773 align:middle line:90% that you're technically not-- 00:13:39.773 --> 00:13:42.190 align:middle line:84% so, when you do this calculation of integrating over 4 pi, 00:13:42.190 --> 00:13:44.020 align:middle line:84% you're assuming some spherical symmetry. 00:13:44.020 --> 00:13:45.160 align:middle line:90% But we know for a fact-- 00:13:45.160 --> 00:13:46.618 align:middle line:84% MARIA GATU JOHNSON: Great question. 00:13:46.618 --> 00:13:48.710 align:middle line:90% 00:13:48.710 --> 00:13:52.150 align:middle line:84% So in ICF, actually, you can typically assume 4 pi. 00:13:52.150 --> 00:13:54.550 align:middle line:84% There are some variations, which we can look at-- 00:13:54.550 --> 00:13:57.080 align:middle line:90% will look at later in the talk. 00:13:57.080 --> 00:13:58.750 align:middle line:84% But in magnetic confinement fusion, 00:13:58.750 --> 00:14:00.340 align:middle line:90% you don't have 4 pi symmetry. 00:14:00.340 --> 00:14:02.940 align:middle line:84% So then you have to correct for it. 00:14:02.940 --> 00:14:05.940 align:middle line:84% And actually, this leads to the work that you are doing. 00:14:05.940 --> 00:14:08.430 align:middle line:84% This is an example from a paper in 2010 00:14:08.430 --> 00:14:12.690 align:middle line:84% by Sjostrand, where he's using a neutron spectrometer 00:14:12.690 --> 00:14:14.572 align:middle line:84% to infer the total yield of neutrons 00:14:14.572 --> 00:14:15.780 align:middle line:90% from the [INAUDIBLE] tokamak. 00:14:15.780 --> 00:14:18.270 align:middle line:84% But he needs to correct for the emission profile 00:14:18.270 --> 00:14:22.500 align:middle line:84% by using the profile monitor so he can scale 00:14:22.500 --> 00:14:25.980 align:middle line:84% that single line of sight [INAUDIBLE] neutrons 00:14:25.980 --> 00:14:29.955 align:middle line:84% to what the [INAUDIBLE] emission would look like. 00:14:29.955 --> 00:14:30.580 align:middle line:90% Great question. 00:14:30.580 --> 00:14:33.270 align:middle line:90% 00:14:33.270 --> 00:14:35.220 align:middle line:90% OK. 00:14:35.220 --> 00:14:39.120 align:middle line:84% OK, so, thinking about what happens to the particles 00:14:39.120 --> 00:14:42.450 align:middle line:84% after they're born, most nutrients escape an implosion 00:14:42.450 --> 00:14:44.770 align:middle line:90% and can be counted. 00:14:44.770 --> 00:14:47.515 align:middle line:90% But some of them scatter. 00:14:47.515 --> 00:14:48.890 align:middle line:84% We'll talk more about that later. 00:14:48.890 --> 00:14:53.620 align:middle line:84% But for charged fusion products, like from the helium 3 reaction, 00:14:53.620 --> 00:14:56.240 align:middle line:84% stopping in the assembled fuel has to be considered. 00:14:56.240 --> 00:14:58.507 align:middle line:84% So the nutrients, they might scatter on their way out, 00:14:58.507 --> 00:14:59.590 align:middle line:90% lose some of their energy. 00:14:59.590 --> 00:15:01.300 align:middle line:84% But most of them escape directly. 00:15:01.300 --> 00:15:04.990 align:middle line:84% Scattering probability is relatively low. 00:15:04.990 --> 00:15:07.960 align:middle line:84% Any charged particles are going to lose energy as they 00:15:07.960 --> 00:15:10.420 align:middle line:90% traverse the assembled field. 00:15:10.420 --> 00:15:13.430 align:middle line:84% And in fact, an example of what that can look like, 00:15:13.430 --> 00:15:18.070 align:middle line:84% we have the helium 3 critical spectrum be born in 14.7 MeV. 00:15:18.070 --> 00:15:20.410 align:middle line:84% This is the lower [INAUDIBLE] implosion, 00:15:20.410 --> 00:15:24.490 align:middle line:84% lose just a little bit of energy on its way out of the capsule. 00:15:24.490 --> 00:15:27.280 align:middle line:84% For high convergence implosions with high rho R, 00:15:27.280 --> 00:15:29.650 align:middle line:84% the ions will be fully stopped and can't be counted. 00:15:29.650 --> 00:15:33.100 align:middle line:84% So then we really can't rely on measuring primary fusion 00:15:33.100 --> 00:15:37.390 align:middle line:84% products, charged fusion products, for those experiments. 00:15:37.390 --> 00:15:39.970 align:middle line:84% And actually, it turns out that ion stopping plasmas 00:15:39.970 --> 00:15:44.390 align:middle line:84% is a rich research topic that our group has been working on. 00:15:44.390 --> 00:15:46.160 align:middle line:84% I have a few example references there, 00:15:46.160 --> 00:15:48.230 align:middle line:84% and there are a lot of other references. 00:15:48.230 --> 00:15:51.240 align:middle line:90% 00:15:51.240 --> 00:15:52.890 align:middle line:90% OK, let's see. 00:15:52.890 --> 00:15:56.980 align:middle line:84% Yes, so coming back a little bit to the knock-on reactions. 00:15:56.980 --> 00:16:03.480 align:middle line:84% So the neutrons, when they scatter off the fuel ions, 00:16:03.480 --> 00:16:06.720 align:middle line:84% they will also up scatter the fuel ions and energy. 00:16:06.720 --> 00:16:11.430 align:middle line:84% So fuel ions that are starting the thermal distribution, 00:16:11.430 --> 00:16:15.120 align:middle line:84% or basically, coal, can be up scattered in much higher energy 00:16:15.120 --> 00:16:17.460 align:middle line:90% by these 14 MeV neutrons. 00:16:17.460 --> 00:16:19.877 align:middle line:84% The energy of the ion can be calculated according 00:16:19.877 --> 00:16:24.180 align:middle line:84% to that equation, where A is the mass number of the scattering 00:16:24.180 --> 00:16:25.630 align:middle line:90% nucleus. 00:16:25.630 --> 00:16:29.090 align:middle line:84% And theta is the scattering angle. 00:16:29.090 --> 00:16:31.360 align:middle line:90% En is the neutron energy. 00:16:31.360 --> 00:16:33.980 align:middle line:84% And this is the examples of what it can look like. 00:16:33.980 --> 00:16:39.790 align:middle line:84% So this is the scattered spectrum for tritons, deuterons, 00:16:39.790 --> 00:16:40.750 align:middle line:90% and protons. 00:16:40.750 --> 00:16:47.230 align:middle line:84% And basically, the energy of a deuteron tritonal proton 00:16:47.230 --> 00:16:48.790 align:middle line:84% that's scattered in this way is going 00:16:48.790 --> 00:16:50.570 align:middle line:84% to depend on the scattering angle. 00:16:50.570 --> 00:16:52.450 align:middle line:84% So this is what you get if you integrate over 00:16:52.450 --> 00:16:53.914 align:middle line:90% all scattered [INAUDIBLE]. 00:16:53.914 --> 00:16:57.180 align:middle line:90% 00:16:57.180 --> 00:17:00.560 align:middle line:90% OK, and we can use this fact. 00:17:00.560 --> 00:17:04.220 align:middle line:90% We often measure these products. 00:17:04.220 --> 00:17:06.710 align:middle line:84% And we use a number of those products 00:17:06.710 --> 00:17:11.359 align:middle line:84% to infer areal density because the areal density depends 00:17:11.359 --> 00:17:15.710 align:middle line:84% on the ratio or scale, basically the opposite. 00:17:15.710 --> 00:17:19.670 align:middle line:84% The ratio of the number of knock-on ions to the neutron 00:17:19.670 --> 00:17:23.425 align:middle line:84% yield will be a function of the areal density. 00:17:23.425 --> 00:17:24.300 align:middle line:90% Does that make sense? 00:17:24.300 --> 00:17:27.270 align:middle line:84% The more fuel that's assembled, the more of the neutrons 00:17:27.270 --> 00:17:29.810 align:middle line:90% are going to scatter. 00:17:29.810 --> 00:17:31.540 align:middle line:84% So we can use that relationship to infer 00:17:31.540 --> 00:17:33.290 align:middle line:84% what the areal density of an implosion is. 00:17:33.290 --> 00:17:36.410 align:middle line:84% But this only works up to a certain areal density. 00:17:36.410 --> 00:17:38.580 align:middle line:84% Like, the knock-on deuterons, for example, 00:17:38.580 --> 00:17:42.980 align:middle line:84% would be fully ranged out [INAUDIBLE] 200 milligrams. 00:17:42.980 --> 00:17:45.710 align:middle line:84% And we talked about before, it might be at the order 2 00:17:45.710 --> 00:17:47.360 align:middle line:90% grams per centimeter squared. 00:17:47.360 --> 00:17:50.433 align:middle line:84% So this is really relatively low performing implosions 00:17:50.433 --> 00:17:51.350 align:middle line:90% that we're looking at. 00:17:51.350 --> 00:17:55.730 align:middle line:90% 00:17:55.730 --> 00:17:58.450 align:middle line:84% So we often look at the neutrons instead. 00:17:58.450 --> 00:18:01.150 align:middle line:84% And we can derive the energy of the scattered neutrons 00:18:01.150 --> 00:18:03.730 align:middle line:84% to see that the neutrons carry information 00:18:03.730 --> 00:18:06.730 align:middle line:84% about the symmetry of the assembled plasma. 00:18:06.730 --> 00:18:09.930 align:middle line:84% Because again, the scattered neutron energy 00:18:09.930 --> 00:18:12.810 align:middle line:84% will depend on the mass number of the scattering nucleus 00:18:12.810 --> 00:18:15.090 align:middle line:90% and the scattering angle. 00:18:15.090 --> 00:18:19.290 align:middle line:84% So we find, if we do that math, that for a detector at a set 00:18:19.290 --> 00:18:22.350 align:middle line:84% angle [INAUDIBLE] implosion, neutrons 00:18:22.350 --> 00:18:26.160 align:middle line:84% that end up at the detector in a certain energy range 00:18:26.160 --> 00:18:28.080 align:middle line:84% are going to be sampling a certain part 00:18:28.080 --> 00:18:30.820 align:middle line:90% of the shell of the implosion. 00:18:30.820 --> 00:18:36.370 align:middle line:84% So at the NIF in particular, we often infer that compression 00:18:36.370 --> 00:18:39.790 align:middle line:84% by looking at energy range 10 to 12 MeV, which 00:18:39.790 --> 00:18:42.430 align:middle line:84% is a really clean energy range of the neutron spectrum. 00:18:42.430 --> 00:18:44.800 align:middle line:84% I think I might have an example later where you can see. 00:18:44.800 --> 00:18:47.538 align:middle line:84% There are no other sources of neutrons that 00:18:47.538 --> 00:18:48.830 align:middle line:90% might contribute in that range. 00:18:48.830 --> 00:18:51.080 align:middle line:84% So by looking at the number of neutrons in that range, 00:18:51.080 --> 00:18:54.550 align:middle line:84% you really get a measurement of only the neutrons 00:18:54.550 --> 00:18:56.733 align:middle line:90% that are scattered. 00:18:56.733 --> 00:18:58.150 align:middle line:84% OK, so if you do that, if you look 00:18:58.150 --> 00:19:01.228 align:middle line:84% at the range from 10 to 12 MeV, the neutrons 00:19:01.228 --> 00:19:02.520 align:middle line:90% are scattered out from tritons. 00:19:02.520 --> 00:19:03.850 align:middle line:90% It's part of the shell. 00:19:03.850 --> 00:19:06.648 align:middle line:84% Neutrons are scared of the [INAUDIBLE] part of the shell. 00:19:06.648 --> 00:19:09.190 align:middle line:84% And it's a little bit different because deuterons and tritons 00:19:09.190 --> 00:19:12.680 align:middle line:90% have a different mass. 00:19:12.680 --> 00:19:14.230 align:middle line:84% And you can also broaden the range, 00:19:14.230 --> 00:19:16.810 align:middle line:84% and actually, we'll look a little bit at neutron imaging. 00:19:16.810 --> 00:19:20.830 align:middle line:84% Neutron imaging typically looks over a broader neutron energy 00:19:20.830 --> 00:19:24.190 align:middle line:84% range in order to get enough statistics in the sample 00:19:24.190 --> 00:19:26.000 align:middle line:90% the broader part of the shell. 00:19:26.000 --> 00:19:28.000 align:middle line:84% So OK, this looks nice and simple. 00:19:28.000 --> 00:19:31.330 align:middle line:84% In reality, typically, the source of [INAUDIBLE] 00:19:31.330 --> 00:19:32.780 align:middle line:90% is significantly broader. 00:19:32.780 --> 00:19:33.767 align:middle line:90% So this smears out. 00:19:33.767 --> 00:19:36.100 align:middle line:84% You're not going to have all the neutrons coming exactly 00:19:36.100 --> 00:19:36.940 align:middle line:90% from the center. 00:19:36.940 --> 00:19:38.920 align:middle line:90% But this is the basic idea. 00:19:38.920 --> 00:19:42.190 align:middle line:90% 00:19:42.190 --> 00:19:44.500 align:middle line:84% The unscattered energy spectrum, the neutrons 00:19:44.500 --> 00:19:46.750 align:middle line:84% that go straight out, like the green arrow here 00:19:46.750 --> 00:19:49.420 align:middle line:84% that don't lose energy on the way out, 00:19:49.420 --> 00:19:52.300 align:middle line:84% will carry information about ion temperature and velocity 00:19:52.300 --> 00:19:53.470 align:middle line:90% of the assembled fuel. 00:19:53.470 --> 00:19:55.540 align:middle line:84% And actually, in principle, this will 00:19:55.540 --> 00:19:57.520 align:middle line:90% be true of any fusion products. 00:19:57.520 --> 00:20:00.620 align:middle line:84% When they're born, they will be born with this information. 00:20:00.620 --> 00:20:02.890 align:middle line:84% The problem is, if it's a charged fusion product, 00:20:02.890 --> 00:20:04.810 align:middle line:84% it's going to lose a lot of that information 00:20:04.810 --> 00:20:07.560 align:middle line:84% as it's losing energy on the way out of the capsule. 00:20:07.560 --> 00:20:12.170 align:middle line:84% It's going to be a lot harder to infer that information. 00:20:12.170 --> 00:20:16.270 align:middle line:84% This is the expression for the energy of a single fusion 00:20:16.270 --> 00:20:17.260 align:middle line:90% product. 00:20:17.260 --> 00:20:20.740 align:middle line:84% Then we can make the moments of this energy 00:20:20.740 --> 00:20:23.710 align:middle line:84% over the distribution of reactant plans 00:20:23.710 --> 00:20:26.230 align:middle line:84% to find that the width of the neutron spectrum 00:20:26.230 --> 00:20:28.300 align:middle line:84% is proportional to the ion temperature. 00:20:28.300 --> 00:20:30.820 align:middle line:84% There's a small ion temperature related 00:20:30.820 --> 00:20:32.830 align:middle line:90% peak up shift of the spectrum. 00:20:32.830 --> 00:20:36.400 align:middle line:84% And the peak will be shifted to the direction 00:20:36.400 --> 00:20:38.440 align:middle line:90% of flow of the emitting plasma. 00:20:38.440 --> 00:20:40.540 align:middle line:84% There's actually one piece of key information 00:20:40.540 --> 00:20:42.670 align:middle line:84% that we've gotten from neutron data at NIF. 00:20:42.670 --> 00:20:45.760 align:middle line:84% They found early on that the capsule, 00:20:45.760 --> 00:20:48.470 align:middle line:84% when it was pushed through the lasers, 00:20:48.470 --> 00:20:50.570 align:middle line:84% it ran off in one direction, basically, 00:20:50.570 --> 00:20:53.120 align:middle line:84% based on the neutron spectrum being shifted, 00:20:53.120 --> 00:20:56.210 align:middle line:84% which we had to correct for because that prevented 00:20:56.210 --> 00:20:58.430 align:middle line:84% efficient conversion of the compression energy 00:20:58.430 --> 00:20:59.915 align:middle line:84% into thermal energy of the capsule. 00:20:59.915 --> 00:21:03.140 align:middle line:90% 00:21:03.140 --> 00:21:05.900 align:middle line:84% So this is a non-relativistic expression. 00:21:05.900 --> 00:21:07.940 align:middle line:84% Really recommend you read this paper 00:21:07.940 --> 00:21:09.940 align:middle line:84% to get the relativistic math for how this works. 00:21:09.940 --> 00:21:11.482 align:middle line:84% I'm not going to go through it today, 00:21:11.482 --> 00:21:13.190 align:middle line:84% but this is an excellent reference 00:21:13.190 --> 00:21:16.430 align:middle line:84% which everyone that does neutron diagnostics for ICF 00:21:16.430 --> 00:21:18.940 align:middle line:90% uses all the time. 00:21:18.940 --> 00:21:20.843 align:middle line:84% And it's actually, originally, comes 00:21:20.843 --> 00:21:22.510 align:middle line:84% from the magnetic confinement community. 00:21:22.510 --> 00:21:26.290 align:middle line:84% So it's another example of the connections. 00:21:26.290 --> 00:21:28.630 align:middle line:84% OK, so I think by now you've understood 00:21:28.630 --> 00:21:30.670 align:middle line:84% that the neutron spectrum provides information 00:21:30.670 --> 00:21:33.680 align:middle line:84% on areal density, iron temperature, and yield. 00:21:33.680 --> 00:21:37.130 align:middle line:84% And this is an example of what a neutron spectrum can look like. 00:21:37.130 --> 00:21:40.330 align:middle line:84% So the primary [INAUDIBLE] here that are unscattered 00:21:40.330 --> 00:21:44.500 align:middle line:84% [INAUDIBLE], the width of that primary spectrum 00:21:44.500 --> 00:21:49.480 align:middle line:84% is related to the ion temperature of the plasma. 00:21:49.480 --> 00:21:51.620 align:middle line:84% We can also-- not illustrated here-- 00:21:51.620 --> 00:21:54.910 align:middle line:84% but we can have an upshift that's related to the velocity. 00:21:54.910 --> 00:21:57.550 align:middle line:84% And then by counting them, we get the yield, 00:21:57.550 --> 00:21:59.140 align:middle line:90% scaling up to 4 pi. 00:21:59.140 --> 00:22:02.560 align:middle line:84% And then by taking the ratio of the neutrons 00:22:02.560 --> 00:22:06.280 align:middle line:84% in the down scattered range, the neutrons in the primary range, 00:22:06.280 --> 00:22:08.020 align:middle line:84% we get a measure of the areal density. 00:22:08.020 --> 00:22:12.250 align:middle line:84% And actually, we often talk about a down scatter ratio 00:22:12.250 --> 00:22:13.960 align:middle line:84% rather than an areal density because we 00:22:13.960 --> 00:22:16.388 align:middle line:84% can measure the number of neutrons in this range 00:22:16.388 --> 00:22:18.430 align:middle line:84% compared to the number of neutrons in this range. 00:22:18.430 --> 00:22:20.033 align:middle line:90% And, yeah, go ahead. 00:22:20.033 --> 00:22:22.700 align:middle line:84% AUDIENCE: How do you distinguish between neutrons that have down 00:22:22.700 --> 00:22:25.280 align:middle line:84% scattered within the fuel versus neutrons that have down 00:22:25.280 --> 00:22:27.740 align:middle line:90% scattered in the lab? 00:22:27.740 --> 00:22:30.950 align:middle line:84% MARIA GATU JOHNSON: OK, so that becomes a technicality 00:22:30.950 --> 00:22:31.760 align:middle line:90% of the instruments. 00:22:31.760 --> 00:22:34.160 align:middle line:84% You have to collimate them really well 00:22:34.160 --> 00:22:35.930 align:middle line:90% in order to look at that. 00:22:35.930 --> 00:22:39.440 align:middle line:84% And it turns out the way that ICF is set up, 00:22:39.440 --> 00:22:42.680 align:middle line:84% the capsule is at the center of a large chamber. 00:22:42.680 --> 00:22:45.860 align:middle line:84% So the room return from the back wall of the chamber 00:22:45.860 --> 00:22:47.570 align:middle line:84% becomes a much, much smaller fraction 00:22:47.570 --> 00:22:49.670 align:middle line:84% of the neutrons that go down your line of sight. 00:22:49.670 --> 00:22:56.380 align:middle line:84% So basically, the way it's set up for-- 00:22:56.380 --> 00:22:58.540 align:middle line:84% Chris is actually looking at exactly this problem-- 00:22:58.540 --> 00:23:00.582 align:middle line:84% for the magnetic recoil spectrometer, which we'll 00:23:00.582 --> 00:23:03.100 align:middle line:84% be talking about later, the foil is 26 centimeters 00:23:03.100 --> 00:23:06.232 align:middle line:84% from target chamber center, back almost 5 meters away. 00:23:06.232 --> 00:23:08.440 align:middle line:84% So the solid angle for scattered neutrons coming down 00:23:08.440 --> 00:23:10.500 align:middle line:84% the same line of sight is just so much smaller. 00:23:10.500 --> 00:23:12.430 align:middle line:90% It becomes negligible. 00:23:12.430 --> 00:23:14.980 align:middle line:84% For the [INAUDIBLE], I don't think 00:23:14.980 --> 00:23:18.340 align:middle line:84% it's been [INAUDIBLE] I don't think 00:23:18.340 --> 00:23:19.840 align:middle line:90% it's been looked at in detail. 00:23:19.840 --> 00:23:22.270 align:middle line:84% But what they do is they take reference implosions so 00:23:22.270 --> 00:23:24.190 align:middle line:84% that they know if there's no assembled rho R, 00:23:24.190 --> 00:23:28.130 align:middle line:84% they know what the background in that range is. 00:23:28.130 --> 00:23:29.185 align:middle line:90% Yeah. 00:23:29.185 --> 00:23:31.310 align:middle line:84% And then Chris is looking at the concept of putting 00:23:31.310 --> 00:23:33.000 align:middle line:90% numerous foil really far away. 00:23:33.000 --> 00:23:34.498 align:middle line:84% And I'm making him do simulations 00:23:34.498 --> 00:23:36.290 align:middle line:84% to see if that's going to work, or if we're 00:23:36.290 --> 00:23:41.510 align:middle line:84% going to have a problem with the returns [INAUDIBLE]. 00:23:41.510 --> 00:23:45.830 align:middle line:84% AUDIENCE: Why do you cut off the down scattered region at 4 1/2 00:23:45.830 --> 00:23:47.035 align:middle line:90% MeV? 00:23:47.035 --> 00:23:48.410 align:middle line:84% MARIA GATU JOHNSON: OK, so that's 00:23:48.410 --> 00:23:50.600 align:middle line:90% actually just kind of random. 00:23:50.600 --> 00:23:58.425 align:middle line:84% What we typically do when we do this is we [INAUDIBLE] 00:23:58.425 --> 00:24:00.630 align:middle line:84% This is not the best spectrum to look at. 00:24:00.630 --> 00:24:03.800 align:middle line:84% We're gonna see if you can see this on the camera. 00:24:03.800 --> 00:24:07.100 align:middle line:84% We look at DSR, or down scattered ratios, we call it. 00:24:07.100 --> 00:24:12.920 align:middle line:84% And that's the integral in the [INAUDIBLE] sort of see it? 00:24:12.920 --> 00:24:17.090 align:middle line:84% Integral in the 10 to 12 MeV range divided by the 13 to 50 00:24:17.090 --> 00:24:18.170 align:middle line:90% MeV range. 00:24:18.170 --> 00:24:21.730 align:middle line:84% [INAUDIBLE] just get a quantitative number. 00:24:21.730 --> 00:24:25.700 align:middle line:84% So that's this range here divided by that range here. 00:24:25.700 --> 00:24:29.080 align:middle line:84% And the reason we look at that range is because we have 00:24:29.080 --> 00:24:32.230 align:middle line:84% contributions from neutrons from the T2 reaction contributing up 00:24:32.230 --> 00:24:34.180 align:middle line:90% to 9 1/2 MeV. 00:24:34.180 --> 00:24:36.040 align:middle line:84% We have the D-D neutrons contributing here. 00:24:36.040 --> 00:24:38.290 align:middle line:84% You can kind of see that peak here. 00:24:38.290 --> 00:24:40.660 align:middle line:84% And there's also multiple scatters 00:24:40.660 --> 00:24:43.210 align:middle line:84% that kind of break the correlation between rho R 00:24:43.210 --> 00:24:45.280 align:middle line:84% and the number of neutrons that you get. 00:24:45.280 --> 00:24:50.590 align:middle line:84% So it's the cleanest reading to look at in the spectrum. 00:24:50.590 --> 00:24:52.908 align:middle line:90% So that's how that works. 00:24:52.908 --> 00:24:55.980 align:middle line:90% 00:24:55.980 --> 00:24:57.080 align:middle line:90% Any other questions? 00:24:57.080 --> 00:25:00.730 align:middle line:90% 00:25:00.730 --> 00:25:03.610 align:middle line:84% OK, so I mentioned that we can also 00:25:03.610 --> 00:25:08.720 align:middle line:84% use the fusion products to look at the spatial emission. 00:25:08.720 --> 00:25:11.830 align:middle line:84% So we can take images of primary and scattered neutrons, 00:25:11.830 --> 00:25:13.420 align:middle line:84% for example, to provide information 00:25:13.420 --> 00:25:16.000 align:middle line:84% on the burned region, size R, and also 00:25:16.000 --> 00:25:19.490 align:middle line:84% the thickness of the high density shell. 00:25:19.490 --> 00:25:22.870 align:middle line:84% So in this case, this is actually a reconstruction, 00:25:22.870 --> 00:25:25.240 align:middle line:84% taking primary images in the 10 to 12 00:25:25.240 --> 00:25:29.320 align:middle line:84% MeV range, down scatter images in the 6 to 12 MeV range, 00:25:29.320 --> 00:25:32.410 align:middle line:84% and then doing a fluence-compensated image, which 00:25:32.410 --> 00:25:34.630 align:middle line:84% gives us this artifact here, which gives us 00:25:34.630 --> 00:25:36.400 align:middle line:84% the picture of the neutron source, which 00:25:36.400 --> 00:25:39.520 align:middle line:84% is the primary neutrons and the high density shell, 00:25:39.520 --> 00:25:40.840 align:middle line:90% which is scattered neutrons. 00:25:40.840 --> 00:25:44.580 align:middle line:90% 00:25:44.580 --> 00:25:47.250 align:middle line:84% And we can measure the nuclear reaction rate 00:25:47.250 --> 00:25:49.470 align:middle line:84% to get information about the confinement time 00:25:49.470 --> 00:25:51.840 align:middle line:84% and the bang time of the implosion. 00:25:51.840 --> 00:25:55.290 align:middle line:90% So what this is here is-- 00:25:55.290 --> 00:25:56.970 align:middle line:84% we call it the Lagrangian plot where 00:25:56.970 --> 00:25:59.190 align:middle line:90% you follow this simulation. 00:25:59.190 --> 00:26:02.670 align:middle line:84% You follow the same fluid element as a function of time. 00:26:02.670 --> 00:26:06.540 align:middle line:84% And then you see that the red is that interface 00:26:06.540 --> 00:26:09.580 align:middle line:84% between the capsule shell and the gas on the inside. 00:26:09.580 --> 00:26:11.930 align:middle line:84% This is for a gas-filled implosion example rather than 00:26:11.930 --> 00:26:14.190 align:middle line:90% the [INAUDIBLE] ETIs. 00:26:14.190 --> 00:26:15.600 align:middle line:90% You drive it with the lasers. 00:26:15.600 --> 00:26:18.300 align:middle line:84% You get ablation of the surface material, which 00:26:18.300 --> 00:26:20.400 align:middle line:84% is why some curves are going off, 00:26:20.400 --> 00:26:22.740 align:middle line:84% and the other curves are compressing inwards 00:26:22.740 --> 00:26:23.873 align:middle line:90% until you get convergence. 00:26:23.873 --> 00:26:26.040 align:middle line:84% The shift you will show in particular moves inwards. 00:26:26.040 --> 00:26:27.650 align:middle line:90% The rest of it is converging. 00:26:27.650 --> 00:26:30.450 align:middle line:84% Get a little bit of burn here when the shocks hit the center, 00:26:30.450 --> 00:26:34.860 align:middle line:84% and you get more burn here where the capsule is 00:26:34.860 --> 00:26:38.760 align:middle line:84% at peak convergence, when it's maximally heated. 00:26:38.760 --> 00:26:41.910 align:middle line:84% And then you can measure the emission history 00:26:41.910 --> 00:26:43.120 align:middle line:90% as a function of time. 00:26:43.120 --> 00:26:46.570 align:middle line:84% And you can see this shock burn and this compression burn. 00:26:46.570 --> 00:26:49.990 align:middle line:84% And this particular example [INAUDIBLE] implosion. 00:26:49.990 --> 00:26:52.960 align:middle line:84% So gas [INAUDIBLE], so then you often 00:26:52.960 --> 00:26:54.270 align:middle line:90% get both of these components. 00:26:54.270 --> 00:26:55.600 align:middle line:84% And then with the implosion, you're 00:26:55.600 --> 00:26:56.933 align:middle line:90% going to have very little shock. 00:26:56.933 --> 00:26:58.960 align:middle line:84% And you can have a lot more compression 00:26:58.960 --> 00:27:02.690 align:middle line:84% where we would be completely dominated by the [INAUDIBLE]. 00:27:02.690 --> 00:27:05.300 align:middle line:84% OK, so those are some examples of the parameters 00:27:05.300 --> 00:27:06.540 align:middle line:90% we're looking for. 00:27:06.540 --> 00:27:08.300 align:middle line:84% So with that, I plan to go into more 00:27:08.300 --> 00:27:10.280 align:middle line:84% about the technical detector details. 00:27:10.280 --> 00:27:14.047 align:middle line:84% So any questions before we move on? 00:27:14.047 --> 00:27:16.005 align:middle line:84% Actually, I have no idea how I'm doing on time. 00:27:16.005 --> 00:27:18.390 align:middle line:84% PROFESSOR: Oh, you've got half an hour-ish. 00:27:18.390 --> 00:27:18.960 align:middle line:84% MARIA GATU JOHNSON: That should be good. 00:27:18.960 --> 00:27:19.627 align:middle line:90% PROFESSOR: Yeah. 00:27:19.627 --> 00:27:22.690 align:middle line:90% 00:27:22.690 --> 00:27:25.080 align:middle line:84% MARIA GATU JOHNSON: OK, then let's jump into it. 00:27:25.080 --> 00:27:26.830 align:middle line:84% So the first one I thought we'd talk about 00:27:26.830 --> 00:27:29.140 align:middle line:84% is nuclear activation diagnostics. 00:27:29.140 --> 00:27:34.440 align:middle line:84% So they're typically based on indium 115, copper 63, 00:27:34.440 --> 00:27:37.840 align:middle line:84% or zirconium 90 isotopes for measurement 00:27:37.840 --> 00:27:42.700 align:middle line:84% of primary D-D or D-T neutron yields. 00:27:42.700 --> 00:27:46.270 align:middle line:84% If you look at D-D first, that's what we use indium. 00:27:46.270 --> 00:27:49.540 align:middle line:84% When a D-D neutron hits the [INAUDIBLE] indium, 00:27:49.540 --> 00:27:54.500 align:middle line:84% we get a isomer and the scattered neutron. 00:27:54.500 --> 00:27:58.400 align:middle line:84% The threshold for that reaction is about 1 1/2 MeV. 00:27:58.400 --> 00:28:02.270 align:middle line:84% And this isomer state will decay, emitting gamma. 00:28:02.270 --> 00:28:04.160 align:middle line:84% But it has to have about 4.5 hours. 00:28:04.160 --> 00:28:06.110 align:middle line:84% And this is the gamma that we count to ensure 00:28:06.110 --> 00:28:09.210 align:middle line:90% how many reactions happen. 00:28:09.210 --> 00:28:14.820 align:middle line:84% On omega, we use copper to measure the D-T yield. 00:28:14.820 --> 00:28:18.450 align:middle line:90% And again, it's copper 63. 00:28:18.450 --> 00:28:20.700 align:middle line:84% And then the neutron [INAUDIBLE] neutron 00:28:20.700 --> 00:28:23.290 align:middle line:84% means copper will be an end-to-end reaction. 00:28:23.290 --> 00:28:26.350 align:middle line:84% So with copper 62 and two neutrons, 00:28:26.350 --> 00:28:27.480 align:middle line:90% threshold is about 11 MeV. 00:28:27.480 --> 00:28:29.355 align:middle line:84% We'll look at the shape of the cross-section. 00:28:29.355 --> 00:28:31.990 align:middle line:90% I think it's on the next slide. 00:28:31.990 --> 00:28:36.765 align:middle line:84% And then what happens is that copper 62 is radioactive, 00:28:36.765 --> 00:28:39.750 align:middle line:90% will decay to nickel 62. 00:28:39.750 --> 00:28:43.540 align:middle line:84% And the half-life for this is 9.8 minutes. 00:28:43.540 --> 00:28:46.890 align:middle line:84% And what we actually count are the gammas here as well. 00:28:46.890 --> 00:28:51.130 align:middle line:84% Zirconium [INAUDIBLE] zirconium 90. 00:28:51.130 --> 00:28:53.010 align:middle line:84% We again get an end-to-end reaction. 00:28:53.010 --> 00:28:55.290 align:middle line:84% Threshold is about 12 MeV in this case, which 00:28:55.290 --> 00:28:59.520 align:middle line:84% means we're really narrowing in on the primary neutrons at 14 00:28:59.520 --> 00:29:00.810 align:middle line:90% MeV. 00:29:00.810 --> 00:29:02.940 align:middle line:90% This is what we use at the NIF. 00:29:02.940 --> 00:29:06.330 align:middle line:84% And again, zirconium 89 is not stable. 00:29:06.330 --> 00:29:09.150 align:middle line:84% The end product that we get is gamma 909 keV, 00:29:09.150 --> 00:29:11.870 align:middle line:90% which is what we're counting. 00:29:11.870 --> 00:29:13.760 align:middle line:90% And if you look at-- 00:29:13.760 --> 00:29:17.300 align:middle line:84% OK, so this first plot has the indium and zirconium reaction 00:29:17.300 --> 00:29:18.230 align:middle line:90% cross-sections. 00:29:18.230 --> 00:29:20.330 align:middle line:84% So you can clearly see why we use 00:29:20.330 --> 00:29:24.080 align:middle line:84% zirconium for D-T. The threshold is at about 12. 00:29:24.080 --> 00:29:26.330 align:middle line:84% Really covers our primary D-T [INAUDIBLE]. 00:29:26.330 --> 00:29:31.040 align:middle line:84% It's also really sharp though, which is actually a useful tool 00:29:31.040 --> 00:29:33.890 align:middle line:84% because if the peak is shifted up or down, 00:29:33.890 --> 00:29:37.160 align:middle line:84% it's going to impact what you're counting, 00:29:37.160 --> 00:29:41.223 align:middle line:84% which means you get an impact of velocity [INAUDIBLE]. 00:29:41.223 --> 00:29:43.800 align:middle line:90% 00:29:43.800 --> 00:29:47.630 align:middle line:84% You so you can see differences around the implosion. 00:29:47.630 --> 00:29:49.970 align:middle line:84% And then indium, on the other hand, 00:29:49.970 --> 00:29:52.450 align:middle line:84% is a really broad cross-section, which actually 00:29:52.450 --> 00:29:55.640 align:middle line:90% makes it a really blunt tool. 00:29:55.640 --> 00:29:59.990 align:middle line:84% If you want to use it to measure D-D, it's by far the easiest. 00:29:59.990 --> 00:30:03.320 align:middle line:84% In a pure D2 implosion, we don't have the down scattered 00:30:03.320 --> 00:30:05.626 align:middle line:90% D-T neutrons [INAUDIBLE] 00:30:05.626 --> 00:30:09.020 align:middle line:90% 00:30:09.020 --> 00:30:10.850 align:middle line:84% In principle, you can use a cocktail 00:30:10.850 --> 00:30:13.010 align:middle line:84% of different nuclear activation detectors 00:30:13.010 --> 00:30:16.288 align:middle line:84% to piece together information about the full neutron spectrum. 00:30:16.288 --> 00:30:18.830 align:middle line:84% And here, we have some examples of parts of the spectrum that 00:30:18.830 --> 00:30:19.800 align:middle line:90% can be of interest. 00:30:19.800 --> 00:30:25.150 align:middle line:84% So in the D-T implosion, this is what the D-D spectrum look like. 00:30:25.150 --> 00:30:27.430 align:middle line:84% You actually have some of those secondary neutrons 00:30:27.430 --> 00:30:30.880 align:middle line:84% that we talked about before that are at 14 MeV. 00:30:30.880 --> 00:30:35.530 align:middle line:84% You have the primary D-Ts at 2 1/2 MeV, down scattered D-Ts, 00:30:35.530 --> 00:30:38.560 align:middle line:84% and then just a little bit of scattered in between. 00:30:38.560 --> 00:30:41.660 align:middle line:84% And that we can get at with the indium in principle. 00:30:41.660 --> 00:30:47.650 align:middle line:84% We have the T-T neutrons, which have a peak at about 9 MeV 00:30:47.650 --> 00:30:50.980 align:middle line:84% and go from 9 1/2 all the way down to 0. 00:30:50.980 --> 00:30:53.500 align:middle line:84% Those you can also attack a little bit. 00:30:53.500 --> 00:30:55.840 align:middle line:84% And then, really, the primary thing we're looking at is 00:30:55.840 --> 00:31:01.690 align:middle line:84% the D-Ts, which some of the up scattered then-- 00:31:01.690 --> 00:31:04.090 align:middle line:90% and we looked at this before-- 00:31:04.090 --> 00:31:07.970 align:middle line:84% where the neutron has hit a fuel ion, giving it a lot of energy. 00:31:07.970 --> 00:31:10.660 align:middle line:84% That energy in turn reacts to produce another neutron. 00:31:10.660 --> 00:31:13.990 align:middle line:84% That's when we get these really high MeV tertiary 00:31:13.990 --> 00:31:16.090 align:middle line:90% neutrons, 15 to 30 MeV. 00:31:16.090 --> 00:31:18.007 align:middle line:84% And that's actually, in many cases, also 00:31:18.007 --> 00:31:19.840 align:middle line:84% really interesting measurements [INAUDIBLE]. 00:31:19.840 --> 00:31:22.645 align:middle line:90% 00:31:22.645 --> 00:31:24.690 align:middle line:84% Oh yeah, that completely fell off. 00:31:24.690 --> 00:31:26.810 align:middle line:84% There's another reaction here that 00:31:26.810 --> 00:31:28.340 align:middle line:90% has this cross-section here. 00:31:28.340 --> 00:31:30.740 align:middle line:84% It's an isotope of carbon, but honestly, 00:31:30.740 --> 00:31:32.060 align:middle line:90% don't remember which one. 00:31:32.060 --> 00:31:35.360 align:middle line:84% So then you can really focus in on just those highest 00:31:35.360 --> 00:31:36.170 align:middle line:90% energy neutrons. 00:31:36.170 --> 00:31:39.560 align:middle line:90% 00:31:39.560 --> 00:31:41.780 align:middle line:84% And this actually also shows you-- 00:31:41.780 --> 00:31:47.160 align:middle line:90% we have-- it's carbon-12. 00:31:47.160 --> 00:31:49.120 align:middle line:90% [INAUDIBLE] 00:31:49.120 --> 00:31:54.580 align:middle line:84% Copper you kind of see is this orange line here. 00:31:54.580 --> 00:31:57.210 align:middle line:84% And we have zirconium as the red line. 00:31:57.210 --> 00:32:01.020 align:middle line:84% So zirconium is a much sharper threshold of 12 MeV. 00:32:01.020 --> 00:32:02.740 align:middle line:90% Copper starts already at 11. 00:32:02.740 --> 00:32:04.800 align:middle line:84% So they have a little bit different sensitivity 00:32:04.800 --> 00:32:07.830 align:middle line:90% to [INAUDIBLE] neutrons. 00:32:07.830 --> 00:32:10.350 align:middle line:84% At omega, copper activation is used 00:32:10.350 --> 00:32:12.810 align:middle line:84% for measurements of the primary DT neutron yield. 00:32:12.810 --> 00:32:16.470 align:middle line:84% We have, basically, a little retractor tube 00:32:16.470 --> 00:32:20.460 align:middle line:84% that allows a puck to be inserted 00:32:20.460 --> 00:32:22.770 align:middle line:84% and then dropped after a shot by pushing a button. 00:32:22.770 --> 00:32:24.510 align:middle line:90% But it's still very manual. 00:32:24.510 --> 00:32:26.520 align:middle line:84% So many times, I've been up there for a shot, 00:32:26.520 --> 00:32:29.880 align:middle line:84% and this old Russian guy, Vladimir Glebov, 00:32:29.880 --> 00:32:32.010 align:middle line:84% pushes the button, gets the black disk, 00:32:32.010 --> 00:32:33.630 align:middle line:84% and then runs it over to the counting 00:32:33.630 --> 00:32:36.740 align:middle line:90% detector in a different lab. 00:32:36.740 --> 00:32:38.520 align:middle line:84% And it's using sodium iodide detectors 00:32:38.520 --> 00:32:42.675 align:middle line:84% to detect the gammas in coincidence [INAUDIBLE]. 00:32:42.675 --> 00:32:45.390 align:middle line:84% And it's actually quite useful because then you 00:32:45.390 --> 00:32:47.860 align:middle line:84% go down to really low neutron thresholds. 00:32:47.860 --> 00:32:50.640 align:middle line:84% So cryogenic implosions at OMEGA produce upwards of 10 00:32:50.640 --> 00:32:53.910 align:middle line:84% to the 14 neutrons, but you can measure neutrons down to 10 00:32:53.910 --> 00:32:57.900 align:middle line:84% to the 7, which means you can look at experiments where you're 00:32:57.900 --> 00:32:59.400 align:middle line:84% not producing many neutrons at all 00:32:59.400 --> 00:33:03.590 align:middle line:90% and still know what you produce. 00:33:03.590 --> 00:33:09.213 align:middle line:84% On the NIF, zirconium is the primary activation element used. 00:33:09.213 --> 00:33:10.880 align:middle line:84% And it's used routinely for measurements 00:33:10.880 --> 00:33:12.290 align:middle line:90% of primary DT neutron yield. 00:33:12.290 --> 00:33:14.340 align:middle line:84% In fact, from the high-performing implosions, 00:33:14.340 --> 00:33:17.360 align:middle line:84% there are two measurements that provide the yield that's 00:33:17.360 --> 00:33:19.170 align:middle line:90% then reported out. 00:33:19.170 --> 00:33:21.740 align:middle line:84% One is the zirconium nuclear activation, 00:33:21.740 --> 00:33:23.890 align:middle line:90% the other one is MRS. 00:33:23.890 --> 00:33:28.910 align:middle line:84% So it's implemented in a number of different versions. 00:33:28.910 --> 00:33:31.900 align:middle line:84% We have the Well-NADs, which is kind of the go-to reference. 00:33:31.900 --> 00:33:36.530 align:middle line:84% It's inserted to 4 meters from target chamber center. 00:33:36.530 --> 00:33:38.230 align:middle line:84% There's three different pucks that 00:33:38.230 --> 00:33:39.850 align:middle line:84% sit very close to each other so you 00:33:39.850 --> 00:33:41.440 align:middle line:84% can compare the numbers from the three 00:33:41.440 --> 00:33:44.050 align:middle line:84% and make sure you're not making any mistakes. 00:33:44.050 --> 00:33:47.620 align:middle line:84% And then you have the Snout-NAD, which 00:33:47.620 --> 00:33:49.400 align:middle line:90% you can insert much closer. 00:33:49.400 --> 00:33:52.450 align:middle line:84% And actually, it's more common to vary the elements 00:33:52.450 --> 00:33:55.210 align:middle line:84% in these packets and have the cocktails to look 00:33:55.210 --> 00:33:57.400 align:middle line:84% at different neutron interactions. 00:33:57.400 --> 00:33:59.710 align:middle line:84% And then finally, you have the Flange-NADs, 00:33:59.710 --> 00:34:02.420 align:middle line:84% which sit on the outside of the chamber. 00:34:02.420 --> 00:34:04.900 align:middle line:84% And there's a large number of those attached 00:34:04.900 --> 00:34:06.640 align:middle line:84% in different positions around the chamber 00:34:06.640 --> 00:34:09.940 align:middle line:90% to look at symmetries. 00:34:09.940 --> 00:34:12.389 align:middle line:84% The zirconium detectors are transported-- well, 00:34:12.389 --> 00:34:16.469 align:middle line:84% actually this is kind of modified to the Flange-NADs-- 00:34:16.469 --> 00:34:17.909 align:middle line:90% we'll talk more about later-- 00:34:17.909 --> 00:34:20.670 align:middle line:84% are now counted in situ at the NIF, 00:34:20.670 --> 00:34:22.260 align:middle line:90% but they used to be transported. 00:34:22.260 --> 00:34:24.090 align:middle line:84% Zirconium detectors are transported 00:34:24.090 --> 00:34:28.050 align:middle line:84% to the Lawrence Livermore National Lab NAD Data Analysis 00:34:28.050 --> 00:34:33.120 align:middle line:84% Facility, which looks like this with some really old hardware 00:34:33.120 --> 00:34:34.469 align:middle line:90% but still does its job. 00:34:34.469 --> 00:34:38.550 align:middle line:90% 00:34:38.550 --> 00:34:41.520 align:middle line:84% And then yeah, so the Flange-NADs has actually 00:34:41.520 --> 00:34:44.429 align:middle line:84% been converted, fairly recently, to 48 00:34:44.429 --> 00:34:48.900 align:middle line:84% real-time zirconium nuclear activation 00:34:48.900 --> 00:34:54.239 align:middle line:84% diagnostics, or RT-NADs, that are permanently installed-- 00:34:54.239 --> 00:34:56.730 align:middle line:84% semi-permanently installed on the chamber 00:34:56.730 --> 00:35:02.400 align:middle line:84% with a lanthanum bromide detector counting the activation 00:35:02.400 --> 00:35:05.080 align:middle line:90% from those continuously. 00:35:05.080 --> 00:35:08.100 align:middle line:84% And you can see the peaks when there is an implosion. 00:35:08.100 --> 00:35:11.100 align:middle line:84% But recently, it used to be 48, which is great. 00:35:11.100 --> 00:35:13.480 align:middle line:84% You can really look at the symmetry of the emission, 00:35:13.480 --> 00:35:14.698 align:middle line:90% which-- 00:35:14.698 --> 00:35:16.490 align:middle line:84% I think I'll get to this on the next slide, 00:35:16.490 --> 00:35:18.980 align:middle line:84% but the symmetry emission tells us about the aereal density 00:35:18.980 --> 00:35:20.340 align:middle line:90% symmetry. 00:35:20.340 --> 00:35:22.090 align:middle line:84% So we could look at the symmetry emission. 00:35:22.090 --> 00:35:24.250 align:middle line:84% The reason high-yield implosions have 00:35:24.250 --> 00:35:28.570 align:middle line:84% started killing these detectors, so we're now down to 21 version, 00:35:28.570 --> 00:35:31.540 align:middle line:84% and we actually have to remove them before every high shot. 00:35:31.540 --> 00:35:37.100 align:middle line:84% So they're no longer permanently installed on the chamber. 00:35:37.100 --> 00:35:37.600 align:middle line:90% Yeah. 00:35:37.600 --> 00:35:40.090 align:middle line:84% So this is what I was trying to get to. 00:35:40.090 --> 00:35:42.550 align:middle line:84% The nuclear activation diagnostics 00:35:42.550 --> 00:35:46.135 align:middle line:84% often show large low-mode aereal density asymmetries 00:35:46.135 --> 00:35:47.150 align:middle line:90% in NIF implosions. 00:35:47.150 --> 00:35:50.860 align:middle line:84% So this is when you have this network of 48 detectors 00:35:50.860 --> 00:35:54.010 align:middle line:84% that all provide a measurement of the yield 00:35:54.010 --> 00:35:56.980 align:middle line:90% above the threshold of 12 MeV. 00:35:56.980 --> 00:35:58.480 align:middle line:84% If you're starting to see variations 00:35:58.480 --> 00:36:01.300 align:middle line:84% in that above-12-MeV threshold, that 00:36:01.300 --> 00:36:06.310 align:middle line:84% means that the birth distribution is uniform in 4 pi. 00:36:06.310 --> 00:36:08.260 align:middle line:84% So that means something must have happened 00:36:08.260 --> 00:36:12.340 align:middle line:84% on the way out, where some of them, more than others, 00:36:12.340 --> 00:36:15.220 align:middle line:84% were scattered on the way out, which 00:36:15.220 --> 00:36:16.840 align:middle line:84% means that the aereal density is not 00:36:16.840 --> 00:36:19.210 align:middle line:90% symmetric around the implosion. 00:36:19.210 --> 00:36:22.060 align:middle line:84% And actually, turns out the typical scattered neutron 00:36:22.060 --> 00:36:23.990 align:middle line:90% fraction is about 20%. 00:36:23.990 --> 00:36:27.672 align:middle line:84% You can look at them, the number density times the cross-section 00:36:27.672 --> 00:36:30.130 align:middle line:84% times the shell thickness, you get just a rough measurement 00:36:30.130 --> 00:36:32.090 align:middle line:84% of how many neutrons will scatter on the way out. 00:36:32.090 --> 00:36:32.755 align:middle line:90% It's about 20%. 00:36:32.755 --> 00:36:36.170 align:middle line:90% 00:36:36.170 --> 00:36:39.020 align:middle line:84% [INAUDIBLE] frequently see variations 00:36:39.020 --> 00:36:42.330 align:middle line:84% of plus/minus 8% in the unscattered neutron yield, 00:36:42.330 --> 00:36:44.420 align:middle line:84% which means it's a large aereal density 00:36:44.420 --> 00:36:47.820 align:middle line:84% variation from one side of the capsule to the other. 00:36:47.820 --> 00:36:50.540 align:middle line:84% And this has also been a really useful diagnostic tool 00:36:50.540 --> 00:36:52.970 align:middle line:84% in figuring out what's going on with these implosions 00:36:52.970 --> 00:36:55.880 align:middle line:84% as we're trying to improve them further, make them perform 00:36:55.880 --> 00:36:57.260 align:middle line:90% better. 00:36:57.260 --> 00:37:01.630 align:middle line:84% And yeah so I've mentioned before that you also 00:37:01.630 --> 00:37:05.230 align:middle line:84% have an impact on peak shifts here because the cross-section 00:37:05.230 --> 00:37:06.620 align:middle line:90% is higher and higher energy. 00:37:06.620 --> 00:37:09.370 align:middle line:84% So if you have a flow where the [INAUDIBLE] runs off 00:37:09.370 --> 00:37:11.170 align:middle line:84% in one direction, you can have upshift 00:37:11.170 --> 00:37:13.300 align:middle line:84% of the peak in that direction, downshift 00:37:13.300 --> 00:37:14.830 align:middle line:84% of the peak in the other direction. 00:37:14.830 --> 00:37:17.530 align:middle line:84% It turns out it's a smaller effect than the rho R 00:37:17.530 --> 00:37:19.232 align:middle line:84% asymmetries, but it's significant enough 00:37:19.232 --> 00:37:20.440 align:middle line:90% where it has to be corrected. 00:37:20.440 --> 00:37:22.720 align:middle line:84% First, you have to measure that directional flow 00:37:22.720 --> 00:37:27.770 align:middle line:84% and correct the distribution for that effect as well. 00:37:27.770 --> 00:37:32.830 align:middle line:84% And we use low aereal density gas-filled DT exploding pushers 00:37:32.830 --> 00:37:36.856 align:middle line:84% to set the baseline variations, basically, as-- 00:37:36.856 --> 00:37:40.700 align:middle line:90% losing the word-- baselining. 00:37:40.700 --> 00:37:41.967 align:middle line:90% There's another word. 00:37:41.967 --> 00:37:43.175 align:middle line:90% Maybe it'll come to me later. 00:37:43.175 --> 00:37:46.030 align:middle line:90% 00:37:46.030 --> 00:37:47.730 align:middle line:90% OK. 00:37:47.730 --> 00:37:51.768 align:middle line:84% Did that all make sense, nuclear activation detectors? 00:37:51.768 --> 00:37:53.560 align:middle line:84% PROFESSOR: So why is it that you use copper 00:37:53.560 --> 00:37:54.907 align:middle line:90% on OMEGA and zirconium on NIF? 00:37:54.907 --> 00:37:56.740 align:middle line:84% MARIA GATU JOHNSON: Just historical reasons. 00:37:56.740 --> 00:37:58.002 align:middle line:90% PROFESSOR: Oh, OK. 00:37:58.002 --> 00:38:00.210 align:middle line:84% Is one better than the other or that can [INAUDIBLE]? 00:38:00.210 --> 00:38:02.470 align:middle line:84% MARIA GATU JOHNSON: So I actually-- 00:38:02.470 --> 00:38:04.822 align:middle line:84% the guy who runs the neutron diagnostics at OMEGA 00:38:04.822 --> 00:38:08.480 align:middle line:84% now would like to start using zirconium instead. 00:38:08.480 --> 00:38:10.390 align:middle line:90% And if I remember correctly-- 00:38:10.390 --> 00:38:14.300 align:middle line:90% 00:38:14.300 --> 00:38:16.833 align:middle line:84% yeah, the reason for that is the longer half life. 00:38:16.833 --> 00:38:19.000 align:middle line:84% It's really hard to work with a 10-minute half life. 00:38:19.000 --> 00:38:23.620 align:middle line:84% You have to really run to get to that detector 00:38:23.620 --> 00:38:27.582 align:middle line:84% fast enough, whereas zirconium, with the three days, 00:38:27.582 --> 00:38:28.540 align:middle line:90% is a little bit easier. 00:38:28.540 --> 00:38:31.270 align:middle line:84% And also, the threshold's actually better at 12 00:38:31.270 --> 00:38:33.080 align:middle line:90% compared to 11. 00:38:33.080 --> 00:38:33.580 align:middle line:90% Yeah? 00:38:33.580 --> 00:38:36.850 align:middle line:84% AUDIENCE: For looking at the upshift from zirconium, 00:38:36.850 --> 00:38:39.550 align:middle line:84% do you just compare that to a baseline 00:38:39.550 --> 00:38:42.640 align:middle line:84% where you have a more uniform emission 00:38:42.640 --> 00:38:44.470 align:middle line:84% profile versus a non-uniform one, 00:38:44.470 --> 00:38:48.520 align:middle line:84% where that steepness of the cross-section actually matters? 00:38:48.520 --> 00:38:50.680 align:middle line:84% Or do you compare it to a baseline cross-section 00:38:50.680 --> 00:38:53.668 align:middle line:90% that's flatter? 00:38:53.668 --> 00:38:55.460 align:middle line:84% MARIA GATU JOHNSON: I'm not sure if I fully 00:38:55.460 --> 00:38:56.690 align:middle line:90% understand the question. 00:38:56.690 --> 00:38:58.700 align:middle line:84% But so what you're doing is you're 00:38:58.700 --> 00:39:00.743 align:middle line:84% looking in many different directions, 00:39:00.743 --> 00:39:02.910 align:middle line:84% and you compare the results in different directions. 00:39:02.910 --> 00:39:05.227 align:middle line:90% But you know-- 00:39:05.227 --> 00:39:07.310 align:middle line:84% AUDIENCE: So but you just-- you know your baseline 00:39:07.310 --> 00:39:12.050 align:middle line:84% just by assuming a 14.1 MeV uniform profile? 00:39:12.050 --> 00:39:15.050 align:middle line:84% MARIA GATU JOHNSON: OK, so there's a couple steps to this. 00:39:15.050 --> 00:39:18.320 align:middle line:84% If you get a map kind of like this one, 00:39:18.320 --> 00:39:21.320 align:middle line:84% I mentioned you have to correct for the velocity, which 00:39:21.320 --> 00:39:22.520 align:middle line:90% is the peak shift. 00:39:22.520 --> 00:39:25.520 align:middle line:84% We actually don't get the velocity from this diagnostic. 00:39:25.520 --> 00:39:27.860 align:middle line:84% We get it from the neutron spectrometers. 00:39:27.860 --> 00:39:29.450 align:middle line:84% So if you have neutron spectrometers 00:39:29.450 --> 00:39:32.120 align:middle line:84% in six lines of sight, you can measure there. 00:39:32.120 --> 00:39:34.945 align:middle line:84% You don't just measure a number above the threshold, 00:39:34.945 --> 00:39:36.320 align:middle line:84% you actually measure the neutrons 00:39:36.320 --> 00:39:38.150 align:middle line:84% because you know what the option is, 00:39:38.150 --> 00:39:41.810 align:middle line:84% which means you can infer the actual 4 pi velocity vector. 00:39:41.810 --> 00:39:45.198 align:middle line:84% And then you can correct this for that. 00:39:45.198 --> 00:39:45.698 align:middle line:90% Yeah. 00:39:45.698 --> 00:39:48.560 align:middle line:90% 00:39:48.560 --> 00:39:52.420 align:middle line:90% Neutron spectrometers. 00:39:52.420 --> 00:39:56.780 align:middle line:90% Any other activation question? 00:39:56.780 --> 00:39:57.280 align:middle line:90% OK. 00:39:57.280 --> 00:40:00.560 align:middle line:84% Then with that, let's go into neutron spectrometry. 00:40:00.560 --> 00:40:02.800 align:middle line:84% This is kind of touching on exactly that point. 00:40:02.800 --> 00:40:05.250 align:middle line:84% We do have a large suite of neutron spectrometers 00:40:05.250 --> 00:40:08.090 align:middle line:90% on the NIF. 00:40:08.090 --> 00:40:12.350 align:middle line:84% These five, the blue ones here, are all 00:40:12.350 --> 00:40:14.090 align:middle line:90% based on the same technology. 00:40:14.090 --> 00:40:16.850 align:middle line:84% They're neutron time-of-flight spectrometers, 00:40:16.850 --> 00:40:18.510 align:middle line:90% which we'll discuss in detail. 00:40:18.510 --> 00:40:21.110 align:middle line:84% And then this one in red is the magnetic recoil spectrometer, 00:40:21.110 --> 00:40:23.420 align:middle line:84% which I already mentioned a couple of times. 00:40:23.420 --> 00:40:26.480 align:middle line:84% There's actually one more that's not 00:40:26.480 --> 00:40:32.600 align:middle line:84% included on this cartoon, which is also a neutron time-of-flight 00:40:32.600 --> 00:40:35.120 align:middle line:84% spectrometer based on a different detector 00:40:35.120 --> 00:40:40.160 align:middle line:84% technology that's fielded together with the neutron imager 00:40:40.160 --> 00:40:41.968 align:middle line:90% on roughly this line of sight. 00:40:41.968 --> 00:40:43.760 align:middle line:84% It's been a few years since it was working, 00:40:43.760 --> 00:40:45.593 align:middle line:84% but we're trying to bring it back to resolve 00:40:45.593 --> 00:40:47.120 align:middle line:90% some [INAUDIBLE] everything. 00:40:47.120 --> 00:40:50.030 align:middle line:84% So total of seven neutron spectrometers 00:40:50.030 --> 00:40:53.900 align:middle line:84% on the NIF that provide good implosion coverage together. 00:40:53.900 --> 00:40:56.840 align:middle line:84% And this similar setup exists in other ICF facilities. 00:40:56.840 --> 00:40:58.550 align:middle line:84% Like on OMEGA, for example, think 00:40:58.550 --> 00:41:04.323 align:middle line:84% there are six now that run on DT in different lines of sight. 00:41:04.323 --> 00:41:06.740 align:middle line:84% So you can compare the results in those six lines of sight 00:41:06.740 --> 00:41:09.290 align:middle line:84% to, again, infer the flow vector in addition 00:41:09.290 --> 00:41:12.740 align:middle line:84% to measuring the ion temperature and the ion temperature 00:41:12.740 --> 00:41:14.540 align:middle line:90% variations. 00:41:14.540 --> 00:41:17.600 align:middle line:84% And fewer of them work on DT but still enough 00:41:17.600 --> 00:41:19.610 align:middle line:90% to get a good coverage. 00:41:19.610 --> 00:41:22.570 align:middle line:90% 00:41:22.570 --> 00:41:23.070 align:middle line:90% OK. 00:41:23.070 --> 00:41:25.278 align:middle line:84% So let's start with the magnetic recoil spectrometer. 00:41:25.278 --> 00:41:27.150 align:middle line:84% So again, this is what I've been working 00:41:27.150 --> 00:41:32.230 align:middle line:84% with since 2010, so happy to take any questions on this one. 00:41:32.230 --> 00:41:35.320 align:middle line:84% And Chris is working on a very similar concept. 00:41:35.320 --> 00:41:38.590 align:middle line:84% Sean's kind of working on a similar concept, too, for Spark. 00:41:38.590 --> 00:41:41.980 align:middle line:84% So you guys are very familiar with this already. 00:41:41.980 --> 00:41:44.770 align:middle line:84% But for those who have not heard about it before, the way it 00:41:44.770 --> 00:41:46.360 align:middle line:84% works, you will have the neutrons 00:41:46.360 --> 00:41:49.660 align:middle line:84% emitted from target chamber center, that little blue dot. 00:41:49.660 --> 00:41:52.390 align:middle line:84% A fraction of those neutrons will reach a conversion 00:41:52.390 --> 00:41:55.450 align:middle line:84% by the plastic conversion foil, 26 centimeters, 00:41:55.450 --> 00:41:57.910 align:middle line:84% in the case of NIF, from target chamber center. 00:41:57.910 --> 00:42:00.250 align:middle line:84% And this is actually deuterated foil. 00:42:00.250 --> 00:42:03.490 align:middle line:84% So the neutrons that interact with the foil, some of them 00:42:03.490 --> 00:42:04.870 align:middle line:90% will knock out deuterons. 00:42:04.870 --> 00:42:07.150 align:middle line:84% Forward-scattered neutrons will reach 00:42:07.150 --> 00:42:10.030 align:middle line:84% this magnet, which is outside of the target chain wall. 00:42:10.030 --> 00:42:12.110 align:middle line:90% It's just a vacuum in between. 00:42:12.110 --> 00:42:13.450 align:middle line:90% So they all reach the magnet. 00:42:13.450 --> 00:42:15.520 align:middle line:84% And then there is momentum separated 00:42:15.520 --> 00:42:17.950 align:middle line:84% in the magnets [INAUDIBLE] different physical location 00:42:17.950 --> 00:42:20.560 align:middle line:84% of the detector, right, depending on their energy. 00:42:20.560 --> 00:42:23.780 align:middle line:84% Then you use that to reconstruct a recoil deuteron energy 00:42:23.780 --> 00:42:24.280 align:middle line:90% spectrum. 00:42:24.280 --> 00:42:25.780 align:middle line:84% And then from that spectrum, you can 00:42:25.780 --> 00:42:30.070 align:middle line:84% infer what the incident neutron spectrum must have looked like. 00:42:30.070 --> 00:42:33.070 align:middle line:84% We use deuterated plastic, in particular 00:42:33.070 --> 00:42:37.660 align:middle line:84% because the detector we use in this instrument is CR-39, 00:42:37.660 --> 00:42:39.970 align:middle line:84% and it turns out the deuteron tracks are much, much 00:42:39.970 --> 00:42:42.820 align:middle line:84% easier to distinguish above background compared 00:42:42.820 --> 00:42:44.870 align:middle line:90% to using protons. 00:42:44.870 --> 00:42:45.370 align:middle line:90% Yeah. 00:42:45.370 --> 00:42:49.010 align:middle line:84% And we also-- there's a number of detectors with [INAUDIBLE] 00:42:49.010 --> 00:42:52.518 align:middle line:84% the sodium hydroxide, scan them in microscopes after the shot, 00:42:52.518 --> 00:42:53.935 align:middle line:84% and then stitch the data together. 00:42:53.935 --> 00:42:56.870 align:middle line:90% 00:42:56.870 --> 00:42:59.790 align:middle line:84% Looking at-- zooming in on the foil here, 00:42:59.790 --> 00:43:02.750 align:middle line:84% so the neutron will hit a deuteron in the foil. 00:43:02.750 --> 00:43:05.930 align:middle line:84% And then the recoil deuteron energy 00:43:05.930 --> 00:43:08.780 align:middle line:84% will depend on the incident neutron energy, 00:43:08.780 --> 00:43:11.990 align:middle line:84% and then also the energy loss that the deuteron has 00:43:11.990 --> 00:43:15.440 align:middle line:84% from its place of birth until it hits the back of the foil. 00:43:15.440 --> 00:43:17.390 align:middle line:84% So a neutron born at the start of the foil 00:43:17.390 --> 00:43:20.300 align:middle line:84% would come out with a lower energy than a neutron born 00:43:20.300 --> 00:43:22.463 align:middle line:90% at the end of the foil. 00:43:22.463 --> 00:43:24.880 align:middle line:84% And that has to be considered in the analysis of the data. 00:43:24.880 --> 00:43:30.010 align:middle line:90% 00:43:30.010 --> 00:43:34.150 align:middle line:84% We can look at, also, a couple of other aspects of this. 00:43:34.150 --> 00:43:36.030 align:middle line:90% So when I have-- 00:43:36.030 --> 00:43:37.715 align:middle line:84% we used to want a high efficiency 00:43:37.715 --> 00:43:39.840 align:middle line:84% to be able to count all the neutrons that came out. 00:43:39.840 --> 00:43:42.390 align:middle line:84% Today, we're actually running into saturation problems 00:43:42.390 --> 00:43:45.360 align:middle line:84% instead, so we don't really want this to be so high anymore. 00:43:45.360 --> 00:43:51.420 align:middle line:84% But the efficiency of the MRS can be back of the envelope 00:43:51.420 --> 00:43:55.810 align:middle line:84% calculated as the foil solid angle times the number density 00:43:55.810 --> 00:44:00.150 align:middle line:84% for deuterons in the foil times the foil thickness the n, 00:44:00.150 --> 00:44:02.550 align:middle line:84% D differential cross-section for forward scatter, 00:44:02.550 --> 00:44:06.510 align:middle line:84% and the aperture solid angle where the aperture is opening 00:44:06.510 --> 00:44:08.810 align:middle line:90% in front of the magnet. 00:44:08.810 --> 00:44:11.210 align:middle line:84% And you can throw some numbers on that. 00:44:11.210 --> 00:44:12.730 align:middle line:90% This is an example from the NIF. 00:44:12.730 --> 00:44:15.700 align:middle line:84% The foil solid angle will be the area 00:44:15.700 --> 00:44:19.750 align:middle line:84% of the foil divided by the total sphere 00:44:19.750 --> 00:44:22.450 align:middle line:84% at that distance where the foil is sitting. 00:44:22.450 --> 00:44:25.150 align:middle line:84% And then number density, we calculate 00:44:25.150 --> 00:44:27.610 align:middle line:84% based on manufacturer's specifications. 00:44:27.610 --> 00:44:30.040 align:middle line:90% Foil thickness is measured. 00:44:30.040 --> 00:44:33.070 align:middle line:84% This differential cross-section in the forward scatter direction 00:44:33.070 --> 00:44:35.260 align:middle line:90% is roughly this number. 00:44:35.260 --> 00:44:38.410 align:middle line:84% Aperture solid angle take the area of the aperture 00:44:38.410 --> 00:44:41.840 align:middle line:84% and just divided by the foil aperture distance squared. 00:44:41.840 --> 00:44:43.497 align:middle line:84% And this is a correction for the fact 00:44:43.497 --> 00:44:45.580 align:middle line:84% that the aperture actually isn't sitting straight. 00:44:45.580 --> 00:44:47.920 align:middle line:84% It's tilted in front of the magnet. 00:44:47.920 --> 00:44:50.650 align:middle line:84% And then this is the [INAUDIBLE] of the [INAUDIBLE] foil 00:44:50.650 --> 00:44:54.000 align:middle line:84% which you also have to add as the correction. 00:44:54.000 --> 00:44:55.650 align:middle line:90% This gives us a rough number. 00:44:55.650 --> 00:44:59.700 align:middle line:84% In reality, this is not what we use to get the yield number out. 00:44:59.700 --> 00:45:01.872 align:middle line:90% We use MCP simulation. 00:45:01.872 --> 00:45:03.580 align:middle line:84% Actually, I thought on the way over here, 00:45:03.580 --> 00:45:07.320 align:middle line:84% I should have included a slide on MCP because we use MCP a lot 00:45:07.320 --> 00:45:10.483 align:middle line:84% as a tool in understanding the response of the detectors 00:45:10.483 --> 00:45:11.400 align:middle line:90% that we're looking at. 00:45:11.400 --> 00:45:13.690 align:middle line:84% Even for the nuclear activation detectors 00:45:13.690 --> 00:45:16.470 align:middle line:84% that we looked at before, to know how many neutrons 00:45:16.470 --> 00:45:20.190 align:middle line:84% that they see and how many might be scattered before they 00:45:20.190 --> 00:45:22.140 align:middle line:84% hit the nuclear activation detector, 00:45:22.140 --> 00:45:25.740 align:middle line:84% we also have to use Monte Carlo neutron transport 00:45:25.740 --> 00:45:27.030 align:middle line:90% tools such as MCMP. 00:45:27.030 --> 00:45:30.670 align:middle line:84% So it's not just building detectors. 00:45:30.670 --> 00:45:33.190 align:middle line:84% There's a lot of modeling that goes into this as well. 00:45:33.190 --> 00:45:36.080 align:middle line:90% 00:45:36.080 --> 00:45:36.580 align:middle line:90% OK. 00:45:36.580 --> 00:45:39.390 align:middle line:84% We can also look at what we expect for the resolution. 00:45:39.390 --> 00:45:40.920 align:middle line:84% What that is, basically, is if you 00:45:40.920 --> 00:45:48.240 align:middle line:84% have monogenic neutrons emitted from target chamber center going 00:45:48.240 --> 00:45:50.190 align:middle line:84% through that whole system, then we're 00:45:50.190 --> 00:45:52.950 align:middle line:84% going to end up with a wider spectrum than just 00:45:52.950 --> 00:45:56.580 align:middle line:84% monogenic on the MRS. So we look at, 00:45:56.580 --> 00:45:58.470 align:middle line:84% how wide would that spectrum be assuming 00:45:58.470 --> 00:46:01.350 align:middle line:84% we had monogenic neutrons to understand the broadening-- 00:46:01.350 --> 00:46:03.640 align:middle line:90% the instrument of broadening. 00:46:03.640 --> 00:46:06.100 align:middle line:84% So we can look at that as three components. 00:46:06.100 --> 00:46:08.472 align:middle line:84% We have a broadening effect due to the foil thickness. 00:46:08.472 --> 00:46:09.930 align:middle line:84% And this is, again, where deuterons 00:46:09.930 --> 00:46:11.250 align:middle line:84% are born on one end or the other, 00:46:11.250 --> 00:46:13.417 align:middle line:84% and they're going to lose energy as they go through, 00:46:13.417 --> 00:46:14.790 align:middle line:90% which gives you a broadening. 00:46:14.790 --> 00:46:17.040 align:middle line:84% We're going to have broadening based on the scattering 00:46:17.040 --> 00:46:18.030 align:middle line:90% geometry. 00:46:18.030 --> 00:46:20.940 align:middle line:84% We have neutrons that hit the foil head on, 00:46:20.940 --> 00:46:22.370 align:middle line:90% deuterons that go straight out. 00:46:22.370 --> 00:46:24.870 align:middle line:84% But then we also have neutrons that hit one edge of the foil 00:46:24.870 --> 00:46:25.990 align:middle line:90% and go at an angle. 00:46:25.990 --> 00:46:27.880 align:middle line:84% And that gives us a broadening effect. 00:46:27.880 --> 00:46:29.970 align:middle line:84% And then finally, we have some broadening 00:46:29.970 --> 00:46:32.310 align:middle line:84% depending on the ion-optical properties of the magnet. 00:46:32.310 --> 00:46:34.500 align:middle line:84% And that leads us to a total broadening. 00:46:34.500 --> 00:46:38.170 align:middle line:84% And it actually turns out that these are counter-related. 00:46:38.170 --> 00:46:39.870 align:middle line:84% So if you want higher efficiency, 00:46:39.870 --> 00:46:42.810 align:middle line:84% you have to add more foil material, which 00:46:42.810 --> 00:46:45.430 align:middle line:90% also enhances the broadening. 00:46:45.430 --> 00:46:48.220 align:middle line:84% You want a narrow broadening, you want high efficiency, 00:46:48.220 --> 00:46:51.930 align:middle line:84% so it becomes an optimization problem. 00:46:51.930 --> 00:46:54.450 align:middle line:84% In the design of a magnetic recoil spectrometer, 00:46:54.450 --> 00:46:56.850 align:middle line:84% you have to balance efficiency and resolution 00:46:56.850 --> 00:46:58.030 align:middle line:90% against each other. 00:46:58.030 --> 00:47:02.145 align:middle line:84% This is an example for the thin foil magnetic [INAUDIBLE] 00:47:02.145 --> 00:47:06.000 align:middle line:84% spectrometer at JET, which is very similar to MRS 00:47:06.000 --> 00:47:07.650 align:middle line:84% and maybe even more similar to what 00:47:07.650 --> 00:47:09.450 align:middle line:90% Sean is working on for Spark. 00:47:09.450 --> 00:47:13.510 align:middle line:84% So this is looking at proton collimator radius and foil 00:47:13.510 --> 00:47:16.500 align:middle line:84% thickness, and seeing how varying those two will impact 00:47:16.500 --> 00:47:18.090 align:middle line:84% the efficiency and resolution, trying 00:47:18.090 --> 00:47:20.280 align:middle line:84% to find some set points that would 00:47:20.280 --> 00:47:23.730 align:middle line:84% be ideal operation for getting the signal you need 00:47:23.730 --> 00:47:26.070 align:middle line:84% and still having a good enough resolution to make 00:47:26.070 --> 00:47:28.687 align:middle line:90% the measurements you want. 00:47:28.687 --> 00:47:30.270 align:middle line:84% And that, actually, we can take a look 00:47:30.270 --> 00:47:33.306 align:middle line:90% at what that looks like at JET. 00:47:33.306 --> 00:47:37.860 align:middle line:84% This is the MPR magnetic recoil proton spectrometer. 00:47:37.860 --> 00:47:40.470 align:middle line:84% In this case, we do use protons not deuterons, 00:47:40.470 --> 00:47:43.470 align:middle line:84% because they use scintillator detectors they can count protons 00:47:43.470 --> 00:47:45.650 align:middle line:90% without any problems. 00:47:45.650 --> 00:47:48.220 align:middle line:84% This is what it looked like before the shielding was added. 00:47:48.220 --> 00:47:49.480 align:middle line:90% This is the magnet housing. 00:47:49.480 --> 00:47:52.600 align:middle line:84% And we add a lot of shielding to prevent contributions 00:47:52.600 --> 00:47:55.360 align:middle line:84% from scattering neutrons that you don't want to look at. 00:47:55.360 --> 00:47:58.810 align:middle line:84% And it's the same concept as for MRS. You 00:47:58.810 --> 00:48:01.300 align:middle line:84% have the neutrons emitted from the plasma over here. 00:48:01.300 --> 00:48:03.370 align:middle line:84% You have collimators, so they only 00:48:03.370 --> 00:48:05.140 align:middle line:84% look at a certain fraction of them. 00:48:05.140 --> 00:48:10.030 align:middle line:84% The foil is inside the magnet housing here. 00:48:10.030 --> 00:48:13.030 align:middle line:84% The second collimators [INAUDIBLE] the protons 00:48:13.030 --> 00:48:14.380 align:middle line:90% are born in foil here. 00:48:14.380 --> 00:48:17.620 align:middle line:84% And then the protons are momentum 00:48:17.620 --> 00:48:19.330 align:middle line:84% analyzed in the magnet [INAUDIBLE] 00:48:19.330 --> 00:48:22.600 align:middle line:84% in a different physical location on the detector array. 00:48:22.600 --> 00:48:24.580 align:middle line:84% In this case, it's an electromagnet rather than 00:48:24.580 --> 00:48:25.600 align:middle line:90% a permanent-- 00:48:25.600 --> 00:48:27.610 align:middle line:84% maybe I probably forgot to mention that for MRS. 00:48:27.610 --> 00:48:31.520 align:middle line:84% But for MRS, it's a permanent magnet. 00:48:31.520 --> 00:48:33.200 align:middle line:84% An advantage with an electromagnet 00:48:33.200 --> 00:48:35.090 align:middle line:84% is that you can tune it so you can 00:48:35.090 --> 00:48:37.490 align:middle line:90% operate at different energies. 00:48:37.490 --> 00:48:40.520 align:middle line:84% The MPR, in particular, can be tuned to operate either for 14 00:48:40.520 --> 00:48:44.880 align:middle line:84% MeV DT neutrons or 2 and 1/2 MeV neutrons. 00:48:44.880 --> 00:48:48.770 align:middle line:84% And we've used them with the JET tokamak 00:48:48.770 --> 00:48:51.620 align:middle line:90% with an oblique angle like that. 00:48:51.620 --> 00:48:53.450 align:middle line:84% If you look from the top, you can 00:48:53.450 --> 00:48:56.480 align:middle line:84% see how it traverses all the way through the plasma. 00:48:56.480 --> 00:49:00.035 align:middle line:84% PROFESSOR: Why is the oblique angle used? 00:49:00.035 --> 00:49:01.410 align:middle line:84% MARIA GATU JOHNSON: I'm not sure. 00:49:01.410 --> 00:49:03.450 align:middle line:90% That's an interesting choice. 00:49:03.450 --> 00:49:05.070 align:middle line:84% I think it might have actually been 00:49:05.070 --> 00:49:07.320 align:middle line:84% to maximize efficiency because you see 00:49:07.320 --> 00:49:08.640 align:middle line:90% more of the plasma that way. 00:49:08.640 --> 00:49:10.048 align:middle line:90% AUDIENCE: OK. 00:49:10.048 --> 00:49:12.340 align:middle line:84% MARIA GATU JOHNSON: It's a question for, Johan, though. 00:49:12.340 --> 00:49:16.610 align:middle line:84% He was involved in the actual building of this system. 00:49:16.610 --> 00:49:17.110 align:middle line:90% OK. 00:49:17.110 --> 00:49:19.630 align:middle line:84% And then so just look at what a recoil deuteron energy 00:49:19.630 --> 00:49:23.290 align:middle line:84% spectrum can look like, this is an example from the NIF. 00:49:23.290 --> 00:49:25.120 align:middle line:90% It's a really old example. 00:49:25.120 --> 00:49:26.653 align:middle line:84% But you have the primary DT peak, 00:49:26.653 --> 00:49:28.570 align:middle line:84% and then you have the down-scattered neutrons. 00:49:28.570 --> 00:49:30.970 align:middle line:84% And then from this, you infer the total neutron yield 00:49:30.970 --> 00:49:33.520 align:middle line:84% by scaling for height, the aereal density 00:49:33.520 --> 00:49:35.770 align:middle line:84% by comparing the number of neutrons here-- 00:49:35.770 --> 00:49:38.500 align:middle line:84% deuterons here and deuterons here and the ion temperature 00:49:38.500 --> 00:49:39.280 align:middle line:90% from the width. 00:49:39.280 --> 00:49:41.500 align:middle line:84% And what you do when you analyze this kind of data 00:49:41.500 --> 00:49:43.690 align:middle line:84% is you take a model neutron spectrum 00:49:43.690 --> 00:49:46.270 align:middle line:84% and fold it with the instrument response function 00:49:46.270 --> 00:49:50.480 align:middle line:84% simulated using GM-4 or MCP or a combination thereof 00:49:50.480 --> 00:49:52.960 align:middle line:84% and get it on the deuteron energy scale, 00:49:52.960 --> 00:49:55.750 align:middle line:84% and then adjust the ion temperature 00:49:55.750 --> 00:49:58.570 align:middle line:84% the peak position, which is related to velocity, 00:49:58.570 --> 00:50:00.820 align:middle line:84% the amplitude, which is related to yield, 00:50:00.820 --> 00:50:03.250 align:middle line:84% and the rho R, which is related to the down-scatter 00:50:03.250 --> 00:50:05.180 align:middle line:90% relative to primary diffraction. 00:50:05.180 --> 00:50:08.330 align:middle line:84% So you get those numbers out of the analysis. 00:50:08.330 --> 00:50:08.830 align:middle line:90% Yeah? 00:50:08.830 --> 00:50:11.538 align:middle line:84% AUDIENCE: You're going past just fitting a Gaussian to this peak. 00:50:11.538 --> 00:50:14.150 align:middle line:84% You're using a more sophisticated analytic model? 00:50:14.150 --> 00:50:16.360 align:middle line:84% MARIA GATU JOHNSON: So actually, in most cases, 00:50:16.360 --> 00:50:18.640 align:middle line:84% I fit a Gaussian to the peak and then just 00:50:18.640 --> 00:50:23.110 align:middle line:84% have a second component that accounts for the scattering. 00:50:23.110 --> 00:50:26.130 align:middle line:84% But yeah, there are some slightly more advanced models 00:50:26.130 --> 00:50:26.630 align:middle line:90% as well. 00:50:26.630 --> 00:50:28.180 align:middle line:84% And for magnetic confinement fusion, 00:50:28.180 --> 00:50:30.722 align:middle line:84% you'd typically have to have more advanced models because you 00:50:30.722 --> 00:50:34.360 align:middle line:84% have fast ions due to heating that contribute 00:50:34.360 --> 00:50:36.430 align:middle line:90% to broadening of the peak. 00:50:36.430 --> 00:50:38.290 align:middle line:84% And to resolve those, you have to have 00:50:38.290 --> 00:50:41.980 align:middle line:84% a model for the beam-thermal reactions 00:50:41.980 --> 00:50:45.460 align:middle line:84% or the beam-beam reactions that have slightly different shapes. 00:50:45.460 --> 00:50:49.800 align:middle line:84% And you can find the relative contributions of those 00:50:49.800 --> 00:50:53.830 align:middle line:84% by fitting those different shapes to the peak. 00:50:53.830 --> 00:50:57.010 align:middle line:90% Other questions? 00:50:57.010 --> 00:50:57.510 align:middle line:90% OK. 00:50:57.510 --> 00:50:59.760 align:middle line:84% So with that, let's look at the neutron time-of-flight 00:50:59.760 --> 00:51:00.370 align:middle line:90% technique. 00:51:00.370 --> 00:51:04.410 align:middle line:84% So for ICF, this is actually simple 00:51:04.410 --> 00:51:06.420 align:middle line:84% because all the particles are assumed 00:51:06.420 --> 00:51:07.770 align:middle line:90% to be emitted at the same time. 00:51:07.770 --> 00:51:11.500 align:middle line:84% The burn time is so short, order of 100 picoseconds, so you 00:51:11.500 --> 00:51:12.670 align:middle line:90% can make that assumption. 00:51:12.670 --> 00:51:16.140 align:middle line:84% So then you really only have to measure the neutrons 00:51:16.140 --> 00:51:19.320 align:middle line:84% as they arrive on a scintillator at a set distance, d, 00:51:19.320 --> 00:51:20.880 align:middle line:90% from the implosion. 00:51:20.880 --> 00:51:26.885 align:middle line:84% And you use that time to infer the neutron spectrum. 00:51:26.885 --> 00:51:30.240 align:middle line:90% 00:51:30.240 --> 00:51:30.740 align:middle line:90% Yeah. 00:51:30.740 --> 00:51:32.660 align:middle line:84% And I mean, this in particular, it's 00:51:32.660 --> 00:51:35.420 align:middle line:84% already been converted to temperature expression. 00:51:35.420 --> 00:51:37.040 align:middle line:84% But really, what you're looking at 00:51:37.040 --> 00:51:43.570 align:middle line:84% is the neutron energy just on a time scale. 00:51:43.570 --> 00:51:44.350 align:middle line:90% Yeah. 00:51:44.350 --> 00:51:46.367 align:middle line:84% And the same as for MRS, the ion temperature 00:51:46.367 --> 00:51:47.980 align:middle line:90% is determined from the width. 00:51:47.980 --> 00:51:52.860 align:middle line:84% And actually, so on OMEGA, the nTOFs 00:51:52.860 --> 00:51:55.620 align:middle line:84% are still used as the yield measurement, too. 00:51:55.620 --> 00:51:57.540 align:middle line:84% On the NIF, we gave up on that a while ago 00:51:57.540 --> 00:52:03.240 align:middle line:84% because it's so hard to know how the gain of the electronics 00:52:03.240 --> 00:52:05.470 align:middle line:90% [INAUDIBLE] drifts in time. 00:52:05.470 --> 00:52:13.070 align:middle line:84% So what we do is we calibrate it relatively routinely 00:52:13.070 --> 00:52:15.470 align:middle line:84% to the nuclear activation detectors and MRS. 00:52:15.470 --> 00:52:18.080 align:middle line:84% And since it's cross-calibrated, we no longer use it 00:52:18.080 --> 00:52:19.610 align:middle line:90% as the absolute yield number. 00:52:19.610 --> 00:52:24.380 align:middle line:90% 00:52:24.380 --> 00:52:27.770 align:middle line:84% nTOF detectors are also used to diagnose aereal density. 00:52:27.770 --> 00:52:30.800 align:middle line:84% And I think already mentioned at some point that we use that 00:52:30.800 --> 00:52:33.980 align:middle line:84% by comparing to what we call zero rho R implosion, 00:52:33.980 --> 00:52:37.070 align:middle line:84% where we really just put DT gas in the really thin shell, 00:52:37.070 --> 00:52:38.940 align:middle line:84% drive it really hard directly with a laser, 00:52:38.940 --> 00:52:42.740 align:middle line:84% so we know there's no aereal density or negligible aereal 00:52:42.740 --> 00:52:45.490 align:middle line:84% density, and then we can look at the difference between zero rho 00:52:45.490 --> 00:52:49.310 align:middle line:84% R implosion and one with significant rho R to [INAUDIBLE] 00:52:49.310 --> 00:52:52.270 align:middle line:90% the rho R's. 00:52:52.270 --> 00:52:56.350 align:middle line:84% And yeah, this is identifying on the time scale what the 10 to 12 00:52:56.350 --> 00:53:00.580 align:middle line:84% MeV neutron energy range will be. 00:53:00.580 --> 00:53:02.020 align:middle line:90% The detectors at the NIF-- 00:53:02.020 --> 00:53:07.360 align:middle line:84% I think the closest one is 18 meters from the implosion, 00:53:07.360 --> 00:53:11.800 align:middle line:84% and the furthest one is at 27 meters from the implosion. 00:53:11.800 --> 00:53:17.050 align:middle line:84% This is what the original equatorial nTOF looked like. 00:53:17.050 --> 00:53:20.300 align:middle line:84% It's since been upgraded to look more like that. 00:53:20.300 --> 00:53:23.650 align:middle line:84% That actually looks like this, but it's kind of hard to tell. 00:53:23.650 --> 00:53:27.490 align:middle line:84% The way it works now is instead of having these PM 00:53:27.490 --> 00:53:30.040 align:middle line:84% tubes directly attached to the scintillator, which 00:53:30.040 --> 00:53:33.260 align:middle line:84% is in this volume here, like [INAUDIBLE] you 00:53:33.260 --> 00:53:35.300 align:middle line:84% have the photomultiplier tubes facing. 00:53:35.300 --> 00:53:38.090 align:middle line:84% So implosion-- I'm the implosion. 00:53:38.090 --> 00:53:39.380 align:middle line:90% Detector is over here. 00:53:39.380 --> 00:53:42.110 align:middle line:84% The photomultipliers are facing this way so that neutrons 00:53:42.110 --> 00:53:43.730 align:middle line:84% hit the scintillator, and the light 00:53:43.730 --> 00:53:45.080 align:middle line:84% is collected in this direction, so you 00:53:45.080 --> 00:53:47.030 align:middle line:84% have [INAUDIBLE] contributions from scattering 00:53:47.030 --> 00:53:48.860 align:middle line:90% in the detectors themselves. 00:53:48.860 --> 00:53:52.850 align:middle line:84% And there's four photomultiplier tubes at each scintillator, 00:53:52.850 --> 00:53:54.500 align:middle line:84% so you can have different settings 00:53:54.500 --> 00:53:56.030 align:middle line:84% on different photomultiplier tubes 00:53:56.030 --> 00:54:00.013 align:middle line:84% to optimize them to look in different parts of the neutron 00:54:00.013 --> 00:54:00.680 align:middle line:90% energy spectrum. 00:54:00.680 --> 00:54:03.250 align:middle line:90% 00:54:03.250 --> 00:54:04.660 align:middle line:90% There's collimators on the way. 00:54:04.660 --> 00:54:06.910 align:middle line:84% This is an example of how neutrons come through a wall 00:54:06.910 --> 00:54:10.120 align:middle line:90% collimator, with this detector. 00:54:10.120 --> 00:54:13.750 align:middle line:84% In this case, you can also see that both neutrons and gammas 00:54:13.750 --> 00:54:16.930 align:middle line:84% coming through the collimator hit 00:54:16.930 --> 00:54:20.500 align:middle line:84% this high-sensitivity and fast detectors, which 00:54:20.500 --> 00:54:25.090 align:middle line:84% we call a spec detector, which is used to measure rho R. Also 00:54:25.090 --> 00:54:30.670 align:middle line:84% recently installed these quartz Cherenkov detectors to just 00:54:30.670 --> 00:54:33.470 align:middle line:84% a really thin rod in the same line of sight, 00:54:33.470 --> 00:54:36.130 align:middle line:84% which you can use to look at both the neutron and gammas. 00:54:36.130 --> 00:54:40.000 align:middle line:84% And these are actually more optimal for the velocity 00:54:40.000 --> 00:54:42.820 align:middle line:84% measurement because you get a really precise measurement 00:54:42.820 --> 00:54:46.060 align:middle line:84% of the primary structure from those. 00:54:46.060 --> 00:54:46.560 align:middle line:90% Yeah. 00:54:46.560 --> 00:54:48.070 align:middle line:90% And it's similar at OMEGA. 00:54:48.070 --> 00:54:49.230 align:middle line:90% So this is at OMEGA. 00:54:49.230 --> 00:54:51.000 align:middle line:84% It's below the target chamber center 00:54:51.000 --> 00:54:54.000 align:middle line:84% in kind of a basement, which we call LaCave. 00:54:54.000 --> 00:54:59.220 align:middle line:84% It's this large detector which is a liquid scintillator 00:54:59.220 --> 00:54:59.830 align:middle line:90% material. 00:54:59.830 --> 00:55:02.010 align:middle line:84% It's quenched xylene, which allows you to have 00:55:02.010 --> 00:55:03.700 align:middle line:90% a really fast time response. 00:55:03.700 --> 00:55:05.820 align:middle line:84% So it falls off as quickly as possible 00:55:05.820 --> 00:55:08.910 align:middle line:84% after a primary peak, which makes it easier to measure 00:55:08.910 --> 00:55:10.980 align:middle line:90% the down-scattered neutrons. 00:55:10.980 --> 00:55:15.190 align:middle line:84% Actually, another detail-- on OMEGA, the nTOFs times 00:55:15.190 --> 00:55:18.340 align:middle line:84% do not measure down-scattered neutrons in this energy range, 00:55:18.340 --> 00:55:20.710 align:middle line:84% because the rho R is much lower at OMEGA 00:55:20.710 --> 00:55:23.380 align:middle line:84% than on the NIF's much lower-power laser. 00:55:23.380 --> 00:55:26.200 align:middle line:84% So instead, we're using the backscatter edge 00:55:26.200 --> 00:55:28.330 align:middle line:90% of n, D backscattering. 00:55:28.330 --> 00:55:31.720 align:middle line:84% So neutrons that hit the back of the implosion 00:55:31.720 --> 00:55:34.060 align:middle line:84% scatter off of tritium and reach the detector 00:55:34.060 --> 00:55:37.900 align:middle line:84% on this side, which gives us an edge at 3.4 MeV, which is much 00:55:37.900 --> 00:55:40.980 align:middle line:90% easier to distinguish on OMEGA. 00:55:40.980 --> 00:55:42.750 align:middle line:84% And so that's done with this detector. 00:55:42.750 --> 00:55:45.180 align:middle line:84% Again, for photomultiplier tubes, 00:55:45.180 --> 00:55:47.590 align:middle line:84% they're optimized for different ranges of spectrum. 00:55:47.590 --> 00:55:52.470 align:middle line:84% And look closely, you can see there's two detectors in front 00:55:52.470 --> 00:55:53.010 align:middle line:90% here-- 00:55:53.010 --> 00:55:55.350 align:middle line:90% one Cherenkov detector as well-- 00:55:55.350 --> 00:55:57.690 align:middle line:84% that thin rod-- and this pattern detector, 00:55:57.690 --> 00:56:00.490 align:middle line:84% which is one of the primary ion temperature detectors. 00:56:00.490 --> 00:56:03.735 align:middle line:84% So it has much better resolution than with large xylene detector. 00:56:03.735 --> 00:56:08.790 align:middle line:90% 00:56:08.790 --> 00:56:10.090 align:middle line:90% Any questions about that? 00:56:10.090 --> 00:56:10.590 align:middle line:90% Ben? 00:56:10.590 --> 00:56:12.240 align:middle line:84% AUDIENCE: Is the thickness of the detector 00:56:12.240 --> 00:56:13.740 align:middle line:84% a significant source of uncertainty? 00:56:13.740 --> 00:56:16.170 align:middle line:84% I guess I'm guessing that the thickness of these detectors 00:56:16.170 --> 00:56:17.430 align:middle line:84% versus the length of these beam lines 00:56:17.430 --> 00:56:18.840 align:middle line:84% is really small to be negligible. 00:56:18.840 --> 00:56:20.848 align:middle line:84% But is that a source of uncertainty? 00:56:20.848 --> 00:56:23.140 align:middle line:84% MARIA GATU JOHNSON: So it depends on what you mean with 00:56:23.140 --> 00:56:24.010 align:middle line:90% "uncertainty." 00:56:24.010 --> 00:56:27.080 align:middle line:84% I mean, so definitely, you get a broader spectrum 00:56:27.080 --> 00:56:29.080 align:middle line:84% from this large detector than from those thinner 00:56:29.080 --> 00:56:32.720 align:middle line:84% ones in front, which reduces your resolution, 00:56:32.720 --> 00:56:35.130 align:middle line:84% so it's harder to measure ion temperature. 00:56:35.130 --> 00:56:36.890 align:middle line:84% So that's why, like in this case, 00:56:36.890 --> 00:56:40.250 align:middle line:84% this detector is optimized for the rho R measurement, 00:56:40.250 --> 00:56:42.960 align:middle line:84% and this one is optimized for the ion temperature measurement. 00:56:42.960 --> 00:56:46.970 align:middle line:84% This one needs high efficiency to get that weak component 00:56:46.970 --> 00:56:48.480 align:middle line:90% of down-scattered neutrons. 00:56:48.480 --> 00:56:52.315 align:middle line:84% This one needs high resolution to measure the peak accurately. 00:56:52.315 --> 00:56:53.690 align:middle line:84% AUDIENCE: So similar to MRS, it's 00:56:53.690 --> 00:56:55.607 align:middle line:84% a trade-off between efficiency and resolution? 00:56:55.607 --> 00:56:57.900 align:middle line:90% MARIA GATU JOHNSON: Yeah, yeah. 00:56:57.900 --> 00:56:58.400 align:middle line:90% Mm-hmm? 00:56:58.400 --> 00:57:01.430 align:middle line:84% AUDIENCE: Someone asked at APS, and I didn't know why-- 00:57:01.430 --> 00:57:04.940 align:middle line:84% what are the benefits of MRS over the nTOFs if they all 00:57:04.940 --> 00:57:09.340 align:middle line:84% give temperature, rho R, [INAUDIBLE]? 00:57:09.340 --> 00:57:10.810 align:middle line:90% MARIA GATU JOHNSON: So OK. 00:57:10.810 --> 00:57:13.810 align:middle line:84% My perspective, the primary benefit 00:57:13.810 --> 00:57:17.110 align:middle line:84% is having more than one technique because you really 00:57:17.110 --> 00:57:21.027 align:middle line:84% need to know independently what you're measuring. 00:57:21.027 --> 00:57:22.610 align:middle line:84% You can compare the results from both. 00:57:22.610 --> 00:57:25.580 align:middle line:84% And many times over the years, as one technique 00:57:25.580 --> 00:57:27.950 align:middle line:84% started drifting, and then we figure out 00:57:27.950 --> 00:57:30.420 align:middle line:84% what's going wrong by comparing with the other technique. 00:57:30.420 --> 00:57:32.810 align:middle line:84% So I think that's the primary advantage. 00:57:32.810 --> 00:57:35.780 align:middle line:84% You can also say that one is that the MRS gives you 00:57:35.780 --> 00:57:36.650 align:middle line:90% the absolute yield. 00:57:36.650 --> 00:57:38.760 align:middle line:84% It's calibrated from first principles compared 00:57:38.760 --> 00:57:41.670 align:middle line:84% to cross-calibrated to other detectors. 00:57:41.670 --> 00:57:42.170 align:middle line:90% Yeah. 00:57:42.170 --> 00:57:45.050 align:middle line:84% But I think it's really important to have both. 00:57:45.050 --> 00:57:47.090 align:middle line:84% PROFESSOR: But this data is available directly 00:57:47.090 --> 00:57:49.795 align:middle line:84% after the shot, whereas the MRS is a while. 00:57:49.795 --> 00:57:51.670 align:middle line:84% MARIA GATU JOHNSON: That's true, that's true, 00:57:51.670 --> 00:57:53.870 align:middle line:90% which is a huge, huge advantage. 00:57:53.870 --> 00:57:54.435 align:middle line:90% And yeah. 00:57:54.435 --> 00:57:56.060 align:middle line:84% And this could be scaled up to rep rate 00:57:56.060 --> 00:57:59.090 align:middle line:84% as well because you can make sure you can analyze it quickly 00:57:59.090 --> 00:58:02.765 align:middle line:84% after a shot, whereas MRS would CR-39 indefinitely. 00:58:02.765 --> 00:58:04.100 align:middle line:90% [LAUGHTER] 00:58:04.100 --> 00:58:06.380 align:middle line:84% Well, Chris is working on electronic detection, 00:58:06.380 --> 00:58:07.610 align:middle line:90% so we'll get there. 00:58:07.610 --> 00:58:10.320 align:middle line:90% 00:58:10.320 --> 00:58:11.160 align:middle line:90% Other questions? 00:58:11.160 --> 00:58:14.700 align:middle line:90% 00:58:14.700 --> 00:58:15.200 align:middle line:90% OK. 00:58:15.200 --> 00:58:19.970 align:middle line:84% So then the magnetic confinement fusion equivalent-- 00:58:19.970 --> 00:58:22.410 align:middle line:84% we do have a neutron time-of-flight system here, too. 00:58:22.410 --> 00:58:24.285 align:middle line:84% But here, it becomes more complicated 00:58:24.285 --> 00:58:26.660 align:middle line:84% because we can no longer assume that all the neutrons are 00:58:26.660 --> 00:58:28.290 align:middle line:90% emitted at the same time. 00:58:28.290 --> 00:58:30.770 align:middle line:84% So here, we have to have two sets of scintillators. 00:58:30.770 --> 00:58:33.680 align:middle line:84% We have a start scintillator, which we call S1 here, 00:58:33.680 --> 00:58:36.500 align:middle line:84% and a stop scintillator, which is S2. 00:58:36.500 --> 00:58:38.750 align:middle line:84% This is what it actually looks like in real life. 00:58:38.750 --> 00:58:40.790 align:middle line:84% There's a collimator through the floor here. 00:58:40.790 --> 00:58:45.230 align:middle line:84% The detector sitting in the roof lab above the JET tokamak. 00:58:45.230 --> 00:58:48.140 align:middle line:84% So the neutrons come through the collimator in the floor, 00:58:48.140 --> 00:58:51.650 align:middle line:84% hit the start detector first and then the stop detector. 00:58:51.650 --> 00:58:54.500 align:middle line:84% We have the start detectors layered 00:58:54.500 --> 00:58:56.930 align:middle line:84% to allow us to count at a higher rate. 00:58:56.930 --> 00:58:59.120 align:middle line:90% There's five layers in there. 00:58:59.120 --> 00:59:04.972 align:middle line:84% And then the stop detector is divided into 32 segments 00:59:04.972 --> 00:59:07.430 align:middle line:84% to actually-- that's more of a resolution [INAUDIBLE] thing 00:59:07.430 --> 00:59:09.980 align:middle line:84% because you want to know where the light is 00:59:09.980 --> 00:59:16.230 align:middle line:84% coming from in order to be able to measure the [INAUDIBLE]. 00:59:16.230 --> 00:59:20.580 align:middle line:84% And replacing them on the constant time-of-flight 00:59:20.580 --> 00:59:22.740 align:middle line:84% sphere so that you can compare the data 00:59:22.740 --> 00:59:25.680 align:middle line:84% from all the different detectors and stitch to make one spectrum. 00:59:25.680 --> 00:59:26.940 align:middle line:90% Yes, Kai? 00:59:26.940 --> 00:59:29.850 align:middle line:84% AUDIENCE: How do you know if a neutron hits 00:59:29.850 --> 00:59:32.022 align:middle line:84% the S2 is the same one that you just measured at S1? 00:59:32.022 --> 00:59:33.480 align:middle line:84% MARIA GATU JOHNSON: Great question. 00:59:33.480 --> 00:59:34.770 align:middle line:90% So you don't. 00:59:34.770 --> 00:59:36.192 align:middle line:90% And that's where this comes in. 00:59:36.192 --> 00:59:36.900 align:middle line:90% AUDIENCE: Oh, OK. 00:59:36.900 --> 00:59:39.990 align:middle line:84% MARIA GATU JOHNSON: So we look at data 00:59:39.990 --> 00:59:43.560 align:middle line:84% from the different scintillators in coincidence. 00:59:43.560 --> 00:59:45.480 align:middle line:84% So you take-- what this example is, 00:59:45.480 --> 00:59:48.570 align:middle line:84% is all its events that you can get 00:59:48.570 --> 00:59:50.800 align:middle line:90% in the S1 detector on the top. 00:59:50.800 --> 00:59:53.400 align:middle line:84% You get a lot more events in S1 because it's closer 00:59:53.400 --> 00:59:56.500 align:middle line:84% and it's directly in the beam of neutrons from there. 00:59:56.500 --> 00:59:59.460 align:middle line:84% The S2, the beam actually goes through 00:59:59.460 --> 01:00:02.250 align:middle line:84% in the hole in the center, so it doesn't hit the S2 directly. 01:00:02.250 --> 01:00:05.430 align:middle line:84% The S2 only sees scattered neutrons. 01:00:05.430 --> 01:00:07.980 align:middle line:84% But that means you get a lot fewer events in S2's. 01:00:07.980 --> 01:00:12.090 align:middle line:84% And what you do is you go through and look at coincidences 01:00:12.090 --> 01:00:13.380 align:middle line:90% between the two detectors. 01:00:13.380 --> 01:00:16.020 align:middle line:84% And actually, what you get is you get all the coincidences. 01:00:16.020 --> 01:00:17.970 align:middle line:84% You get the true coincidences, and you get 01:00:17.970 --> 01:00:19.740 align:middle line:90% background random coincidences. 01:00:19.740 --> 01:00:22.150 align:middle line:84% And you have to subtract that back out. 01:00:22.150 --> 01:00:24.330 align:middle line:84% But when you do that, the peak will 01:00:24.330 --> 01:00:27.870 align:middle line:84% appear because that's then the true correlation 01:00:27.870 --> 01:00:30.780 align:middle line:84% that it will be the same between all neutrons [INAUDIBLE]. 01:00:30.780 --> 01:00:32.590 align:middle line:90% You were saying? 01:00:32.590 --> 01:00:36.000 align:middle line:84% So in this case, the flight time for a 2 and 1/2 MeV neutron 01:00:36.000 --> 01:00:41.030 align:middle line:84% between S1 and S2 is about 65 nanoseconds. 01:00:41.030 --> 01:00:43.680 align:middle line:84% AUDIENCE: But the beam drift time or the amount of time 01:00:43.680 --> 01:00:45.680 align:middle line:84% that the neutron spends moving between S1 and S2 01:00:45.680 --> 01:00:48.217 align:middle line:84% is very short, because looking like these detectors, 01:00:48.217 --> 01:00:48.800 align:middle line:90% they're very-- 01:00:48.800 --> 01:00:50.430 align:middle line:84% MARIA GATU JOHNSON: 65 nanoseconds. 01:00:50.430 --> 01:00:52.430 align:middle line:84% AUDIENCE: So does this function for DT neutrons, 01:00:52.430 --> 01:00:53.347 align:middle line:90% or is this [INAUDIBLE] 01:00:53.347 --> 01:00:58.040 align:middle line:84% MARIA GATU JOHNSON: So it's best for DB. 01:00:58.040 --> 01:01:02.690 align:middle line:84% So this, it will [INAUDIBLE] they show up at 27 nanoseconds. 01:01:02.690 --> 01:01:05.210 align:middle line:84% The time resolution isn't anywhere near as good 01:01:05.210 --> 01:01:07.370 align:middle line:84% simply because the flight path is shorter. 01:01:07.370 --> 01:01:09.080 align:middle line:84% If you wanted really good resolution, 01:01:09.080 --> 01:01:11.610 align:middle line:84% you'd have to make the flight path really long [INAUDIBLE]. 01:01:11.610 --> 01:01:17.882 align:middle line:90% 01:01:17.882 --> 01:01:19.840 align:middle line:84% But of course, another difference here is here, 01:01:19.840 --> 01:01:24.760 align:middle line:84% we didn't really make that point with the inertial confinement 01:01:24.760 --> 01:01:25.450 align:middle line:90% fusion nTOFs. 01:01:25.450 --> 01:01:27.550 align:middle line:84% But what we're looking at here is running the scintillators 01:01:27.550 --> 01:01:28.217 align:middle line:90% in current mode. 01:01:28.217 --> 01:01:31.360 align:middle line:84% We're just opening them up, looking at the signal current 01:01:31.360 --> 01:01:32.620 align:middle line:90% as a function of time. 01:01:32.620 --> 01:01:35.410 align:middle line:84% In this case, we're looking at individual pulses 01:01:35.410 --> 01:01:38.230 align:middle line:84% from single neutrons interacting with the scintillator. 01:01:38.230 --> 01:01:40.540 align:middle line:84% So we can divide it into-- we recorded 01:01:40.540 --> 01:01:42.260 align:middle line:84% over the entire duration of the pulse 01:01:42.260 --> 01:01:44.830 align:middle line:84% and we can reconstruct neutron spectra for any time 01:01:44.830 --> 01:01:47.120 align:middle line:84% interval we want where we get enough statistics. 01:01:47.120 --> 01:01:50.140 align:middle line:84% So we can actually look at the time evolution of the neutron 01:01:50.140 --> 01:01:52.090 align:middle line:90% spectra this way. 01:01:52.090 --> 01:01:54.907 align:middle line:84% And at ICF, we simply get too many neutrons at the same time 01:01:54.907 --> 01:01:55.990 align:middle line:90% so it becomes complicated. 01:01:55.990 --> 01:01:58.180 align:middle line:84% But Chris has spent quite a bit of time trying to figure out 01:01:58.180 --> 01:01:59.020 align:middle line:90% how to do that, too. 01:01:59.020 --> 01:02:01.630 align:middle line:90% 01:02:01.630 --> 01:02:02.130 align:middle line:90% OK. 01:02:02.130 --> 01:02:04.422 align:middle line:84% So that's all I plan to say about neutron spectrometer. 01:02:04.422 --> 01:02:06.120 align:middle line:84% Any more questions before we move on? 01:02:06.120 --> 01:02:09.630 align:middle line:90% 01:02:09.630 --> 01:02:11.730 align:middle line:90% OK. 01:02:11.730 --> 01:02:13.770 align:middle line:84% OK, I think I have just a very short section 01:02:13.770 --> 01:02:14.710 align:middle line:90% on neutron imaging. 01:02:14.710 --> 01:02:16.740 align:middle line:84% So what we do in neutron imaging is 01:02:16.740 --> 01:02:19.980 align:middle line:84% we use a pinhole or aperture close 01:02:19.980 --> 01:02:21.660 align:middle line:84% to the implosion and the detector 01:02:21.660 --> 01:02:24.700 align:middle line:84% really far away to obtain good magnification. 01:02:24.700 --> 01:02:26.460 align:middle line:90% This is actually very-- 01:02:26.460 --> 01:02:27.960 align:middle line:84% we have the source again here, which 01:02:27.960 --> 01:02:29.460 align:middle line:84% is a target chamber center, which is 01:02:29.460 --> 01:02:30.840 align:middle line:90% where the neutrons are emitted. 01:02:30.840 --> 01:02:34.710 align:middle line:84% You have a lined aperture, which can either 01:02:34.710 --> 01:02:39.270 align:middle line:84% have penumbra, which will encode the signal, 01:02:39.270 --> 01:02:41.940 align:middle line:84% or a simple pinhole, where you have 01:02:41.940 --> 01:02:45.300 align:middle line:84% a direct correlation, basically, between the neutron emission 01:02:45.300 --> 01:02:48.990 align:middle line:84% and opposite, kind of inverted to the detector. 01:02:48.990 --> 01:02:52.620 align:middle line:84% The magnification will depend on the pinhole standoff distance 01:02:52.620 --> 01:02:54.180 align:middle line:90% and the detector distance. 01:02:54.180 --> 01:02:59.280 align:middle line:90% 01:02:59.280 --> 01:03:01.712 align:middle line:84% OK, so I took this slide from somewhere else, 01:03:01.712 --> 01:03:04.170 align:middle line:84% and I don't know what numbers they actually threw in there. 01:03:04.170 --> 01:03:07.780 align:middle line:84% Oh, assuming a magnification of 200, 01:03:07.780 --> 01:03:11.910 align:middle line:84% which you would get depending on what L1 and L2 values you have. 01:03:11.910 --> 01:03:13.740 align:middle line:84% If you have 5 microns at a source, 01:03:13.740 --> 01:03:16.680 align:middle line:84% it's going to be 1 millimeter at the detector, which 01:03:16.680 --> 01:03:18.930 align:middle line:90% magnifies your radius. 01:03:18.930 --> 01:03:21.660 align:middle line:84% I talked about before, that implosion would be 30- 01:03:21.660 --> 01:03:23.280 align:middle line:90% to 50-micron radius. 01:03:23.280 --> 01:03:26.400 align:middle line:84% You magnify them so you can separate individual features 01:03:26.400 --> 01:03:30.030 align:middle line:84% much easier on your detector on the outside of the chamber. 01:03:30.030 --> 01:03:32.100 align:middle line:84% And actually, for the NIF in particular, 01:03:32.100 --> 01:03:35.670 align:middle line:84% I think typically the aperture is about 20 centimeters 01:03:35.670 --> 01:03:37.170 align:middle line:90% from target chamber center. 01:03:37.170 --> 01:03:39.240 align:middle line:90% The detector is 28 meters away. 01:03:39.240 --> 01:03:42.980 align:middle line:90% 01:03:42.980 --> 01:03:45.470 align:middle line:84% Yeah, this is what-- ha, actually, those 01:03:45.470 --> 01:03:47.970 align:middle line:90% are the exact numbers. 01:03:47.970 --> 01:03:49.400 align:middle line:90% So this is what it looks like. 01:03:49.400 --> 01:03:51.470 align:middle line:84% You have the NIF target chamber over here. 01:03:51.470 --> 01:03:53.030 align:middle line:90% That's target chamber center. 01:03:53.030 --> 01:03:55.580 align:middle line:84% The aperture is fielded right here, 20 centimeters 01:03:55.580 --> 01:03:57.680 align:middle line:90% from target chamber center. 01:03:57.680 --> 01:04:02.880 align:middle line:84% And then the neutrons that are selected by the aperture 01:04:02.880 --> 01:04:05.310 align:middle line:84% will travel through this collimator structure 01:04:05.310 --> 01:04:08.640 align:middle line:84% all the way to the detector back here 28 meters away. 01:04:08.640 --> 01:04:11.477 align:middle line:84% And so the neutrons-- this is just a [INAUDIBLE] 01:04:11.477 --> 01:04:12.060 align:middle line:90% it looks like. 01:04:12.060 --> 01:04:13.830 align:middle line:84% The neutrons come out here through 01:04:13.830 --> 01:04:16.260 align:middle line:90% the line-of-sight collimator. 01:04:16.260 --> 01:04:18.322 align:middle line:84% This is that other nTOF detector I talked about. 01:04:18.322 --> 01:04:20.530 align:middle line:84% You can kind of see that it's a different technology. 01:04:20.530 --> 01:04:25.770 align:middle line:84% It's flat plastic scintillators with photomultiplier tubes. 01:04:25.770 --> 01:04:27.210 align:middle line:90% But then the primary-- 01:04:27.210 --> 01:04:29.460 align:middle line:84% so that that's just another neutron spectrometer. 01:04:29.460 --> 01:04:32.280 align:middle line:84% The primary for the imaging system 01:04:32.280 --> 01:04:34.270 align:middle line:84% is the scintillating fiber array, 01:04:34.270 --> 01:04:37.190 align:middle line:84% which is fiber coupled to a camera 01:04:37.190 --> 01:04:39.320 align:middle line:84% and it's done this way in order for you 01:04:39.320 --> 01:04:41.910 align:middle line:84% to be able to gate the camera and get two snapshots. 01:04:41.910 --> 01:04:44.450 align:middle line:84% So you can get the primary neutrons and then 01:04:44.450 --> 01:04:47.540 align:middle line:84% the scattered neutrons at a later time. 01:04:47.540 --> 01:04:51.890 align:middle line:84% There's actually also-- this is the original NIF neutron imaging 01:04:51.890 --> 01:04:52.460 align:middle line:90% system. 01:04:52.460 --> 01:04:54.680 align:middle line:84% There's two more now, so we can look at symmetries 01:04:54.680 --> 01:04:55.730 align:middle line:90% around the chamber. 01:04:55.730 --> 01:04:58.250 align:middle line:84% One of them only has image plate detectors, 01:04:58.250 --> 01:05:01.010 align:middle line:84% which I planned to bring image plate, but I forgot. 01:05:01.010 --> 01:05:01.700 align:middle line:90% But it's-- 01:05:01.700 --> 01:05:06.358 align:middle line:90% 01:05:06.358 --> 01:05:07.900 align:middle line:84% PROFESSOR: We discussed it, actually. 01:05:07.900 --> 01:05:09.160 align:middle line:84% We talked about X-ray diagnostics, 01:05:09.160 --> 01:05:10.490 align:middle line:84% so we talked about it a little bit. 01:05:10.490 --> 01:05:11.070 align:middle line:90% Yeah. 01:05:11.070 --> 01:05:13.300 align:middle line:84% MARIA GATU JOHNSON: Yeah, so you know you can't time gate 01:05:13.300 --> 01:05:14.020 align:middle line:90% on image plates. 01:05:14.020 --> 01:05:16.640 align:middle line:90% So then you just get one image. 01:05:16.640 --> 01:05:17.140 align:middle line:90% OK. 01:05:17.140 --> 01:05:19.810 align:middle line:84% And I wish I had a better picture. 01:05:19.810 --> 01:05:24.260 align:middle line:84% But these pinhole apertures are actually extremely complicated. 01:05:24.260 --> 01:05:26.185 align:middle line:90% So they're made of gold. 01:05:26.185 --> 01:05:28.000 align:middle line:90% They're about that long. 01:05:28.000 --> 01:05:30.070 align:middle line:84% And you have to make pinholes that are 01:05:30.070 --> 01:05:32.560 align:middle line:90% precise all the way through. 01:05:32.560 --> 01:05:34.420 align:middle line:84% It's too hard to drill them circular, 01:05:34.420 --> 01:05:37.000 align:middle line:84% so they make them triangular instead. 01:05:37.000 --> 01:05:39.880 align:middle line:84% And then they're tapered to minimize scatter. 01:05:39.880 --> 01:05:41.560 align:middle line:84% So basically, you have an opening, 01:05:41.560 --> 01:05:44.440 align:middle line:84% and then the neutrons that go through that opening 01:05:44.440 --> 01:05:48.620 align:middle line:84% are all going to be captured at the back end. 01:05:48.620 --> 01:05:53.170 align:middle line:84% None of them are going to stop because of the taper inside. 01:05:53.170 --> 01:05:55.360 align:middle line:84% It's still a really hard machining problem 01:05:55.360 --> 01:05:57.970 align:middle line:84% to get those even triangular pinholes precise 01:05:57.970 --> 01:05:58.880 align:middle line:90% all the way through. 01:05:58.880 --> 01:06:02.110 align:middle line:84% We need gold because, as we talked about, 01:06:02.110 --> 01:06:03.730 align:middle line:84% neutrons have a pretty low likelihood 01:06:03.730 --> 01:06:04.882 align:middle line:90% for interacting in matter. 01:06:04.882 --> 01:06:06.590 align:middle line:84% And you want to only select the ones that 01:06:06.590 --> 01:06:07.548 align:middle line:90% go through the pinhole. 01:06:07.548 --> 01:06:09.410 align:middle line:84% You don't want all the ones around 01:06:09.410 --> 01:06:13.280 align:middle line:84% to also make their way all the way back to the detector. 01:06:13.280 --> 01:06:14.180 align:middle line:90% Yeah. 01:06:14.180 --> 01:06:15.590 align:middle line:90% So that's fun. 01:06:15.590 --> 01:06:17.660 align:middle line:84% And these are examples of the penumbral apertures 01:06:17.660 --> 01:06:21.770 align:middle line:84% where the information will be decoded in the penumbra. 01:06:21.770 --> 01:06:23.600 align:middle line:84% You'll also get straight through neutrons 01:06:23.600 --> 01:06:25.940 align:middle line:84% in [INAUDIBLE] that you can't use 01:06:25.940 --> 01:06:30.524 align:middle line:84% to infer anything about the shape of the implosion. 01:06:30.524 --> 01:06:33.290 align:middle line:84% So this kind of aperture array is 01:06:33.290 --> 01:06:34.940 align:middle line:84% used on all three lines of sight now, 01:06:34.940 --> 01:06:37.850 align:middle line:84% but there's development going on to make it coded aperture, which 01:06:37.850 --> 01:06:41.450 align:middle line:84% is supposedly going to be simpler and thinner and easier 01:06:41.450 --> 01:06:42.490 align:middle line:90% to manufacture. 01:06:42.490 --> 01:06:44.480 align:middle line:84% We'll see if that actually works out. 01:06:44.480 --> 01:06:46.865 align:middle line:90% 01:06:46.865 --> 01:06:47.365 align:middle line:90% See. 01:06:47.365 --> 01:06:50.380 align:middle line:84% Oh, yeah, so these are examples of primary and scattered neutron 01:06:50.380 --> 01:06:50.990 align:middle line:90% images. 01:06:50.990 --> 01:06:53.520 align:middle line:84% And again, they're routinely obtained. 01:06:53.520 --> 01:06:55.953 align:middle line:84% And all DT NIF implosions in these days, 01:06:55.953 --> 01:06:57.370 align:middle line:84% it's even in three lines of sight. 01:06:57.370 --> 01:07:00.230 align:middle line:84% And there's a lot of work going into tomographic reconstructions 01:07:00.230 --> 01:07:03.760 align:middle line:84% to make sure we understand the full emission region. 01:07:03.760 --> 01:07:07.180 align:middle line:84% And we have our equivalent in magnetic confinement fusion, 01:07:07.180 --> 01:07:10.750 align:middle line:90% which John is working on. 01:07:10.750 --> 01:07:13.180 align:middle line:84% And we call them neutron profile cameras. 01:07:13.180 --> 01:07:14.900 align:middle line:84% So it's, again-- the idea, again, 01:07:14.900 --> 01:07:17.740 align:middle line:84% is to probe the shape of the neutron source distribution. 01:07:17.740 --> 01:07:20.510 align:middle line:84% But it's much bigger here and more complicated. 01:07:20.510 --> 01:07:24.040 align:middle line:84% So instead of that pinhole array that's trying to reconstruct 01:07:24.040 --> 01:07:27.600 align:middle line:84% the 50-micron spot, we're looking at a much larger 01:07:27.600 --> 01:07:28.360 align:middle line:90% emission. 01:07:28.360 --> 01:07:31.810 align:middle line:84% And we do it by using a number of different lines of sight 01:07:31.810 --> 01:07:36.840 align:middle line:84% and counting particles along this line of sight, 01:07:36.840 --> 01:07:39.690 align:middle line:84% and then try to reconstruct the full emission [INAUDIBLE]. 01:07:39.690 --> 01:07:41.920 align:middle line:84% And John can answer a lot more questions here. 01:07:41.920 --> 01:07:46.880 align:middle line:90% 01:07:46.880 --> 01:07:47.380 align:middle line:90% OK. 01:07:47.380 --> 01:07:49.570 align:middle line:84% So with that, I'm going to jump right 01:07:49.570 --> 01:07:53.990 align:middle line:84% into charged-particle spectrometry. 01:07:53.990 --> 01:07:56.180 align:middle line:84% And I think I touched on this in the beginning, 01:07:56.180 --> 01:07:57.920 align:middle line:84% but it's routinely used to diagnose 01:07:57.920 --> 01:08:00.800 align:middle line:90% low to medium rho R implosions. 01:08:00.800 --> 01:08:03.740 align:middle line:84% And they can be filled with deuterium, DT, 01:08:03.740 --> 01:08:05.120 align:middle line:90% or D helium-3 fuel. 01:08:05.120 --> 01:08:07.760 align:middle line:84% And the reason we don't typically use it for high rho R 01:08:07.760 --> 01:08:10.280 align:middle line:84% implosions is, again, because the charged particles stop 01:08:10.280 --> 01:08:13.870 align:middle line:84% in the assembled fuel, so they don't become indicators 01:08:13.870 --> 01:08:14.495 align:middle line:90% on the outside. 01:08:14.495 --> 01:08:17.859 align:middle line:90% 01:08:17.859 --> 01:08:18.490 align:middle line:90% OK. 01:08:18.490 --> 01:08:22.720 align:middle line:84% This example is showing the proton 01:08:22.720 --> 01:08:28.479 align:middle line:84% from the interaction for 14.7 MeV downshifted to about 11 MeV 01:08:28.479 --> 01:08:30.700 align:middle line:84% You can look at this downshift to infer 01:08:30.700 --> 01:08:32.710 align:middle line:84% the aereal density, which in this case 01:08:32.710 --> 01:08:35.939 align:middle line:90% was about 84 milligrams. 01:08:35.939 --> 01:08:38.990 align:middle line:84% And you can-- actually, let's see. 01:08:38.990 --> 01:08:40.729 align:middle line:90% Yeah. 01:08:40.729 --> 01:08:44.450 align:middle line:84% I have an example, one with nice [INAUDIBLE] spectrometer. 01:08:44.450 --> 01:08:46.939 align:middle line:84% The cool thing is you can do this thing 01:08:46.939 --> 01:08:48.470 align:middle line:84% in a number of different locations 01:08:48.470 --> 01:08:50.689 align:middle line:84% around the target chamber to look at symmetry again 01:08:50.689 --> 01:08:54.529 align:middle line:84% to see if things are compressed uniformly 01:08:54.529 --> 01:08:58.140 align:middle line:84% or if there's non-uniform issues. 01:08:58.140 --> 01:09:00.590 align:middle line:84% So this is a super simple spectrometer. 01:09:00.590 --> 01:09:04.850 align:middle line:84% We call it wedge range filter spectrometer. 01:09:04.850 --> 01:09:09.271 align:middle line:84% It's just an aluminum filter that's shaped like a wedge. 01:09:09.271 --> 01:09:09.979 align:middle line:90% Pass this around. 01:09:09.979 --> 01:09:10.649 align:middle line:90% You can see it. 01:09:10.649 --> 01:09:15.070 align:middle line:84% So the way this is fielded, it's got a bunch of holes in front. 01:09:15.070 --> 01:09:20.420 align:middle line:84% And you know the holes are used to register where the detector 01:09:20.420 --> 01:09:22.609 align:middle line:90% is fielded behind that wedge. 01:09:22.609 --> 01:09:25.790 align:middle line:84% You know the thickness of the function of precision on this. 01:09:25.790 --> 01:09:30.560 align:middle line:84% And based on, actually, the hole size of the CR-39 detector 01:09:30.560 --> 01:09:32.779 align:middle line:84% as a function of precision relative to those holes, 01:09:32.779 --> 01:09:34.767 align:middle line:84% you infer the proton energy spectrum. 01:09:34.767 --> 01:09:36.350 align:middle line:84% And it's a little bit more complicated 01:09:36.350 --> 01:09:38.899 align:middle line:84% than it sounds because you need to know 01:09:38.899 --> 01:09:42.050 align:middle line:84% the diameter versus energy response of CR-39. 01:09:42.050 --> 01:09:45.890 align:middle line:84% And that varies from piece of CR-39 to piece of CR-39. 01:09:45.890 --> 01:09:48.859 align:middle line:84% So you have to come up with a pretty intricate method 01:09:48.859 --> 01:09:50.689 align:middle line:84% for inferring that from the data. 01:09:50.689 --> 01:09:53.359 align:middle line:84% But that's done, and these are routinely 01:09:53.359 --> 01:09:59.720 align:middle line:84% used to measure rho R from the helium-3 gas-filled implosions 01:09:59.720 --> 01:10:03.572 align:middle line:84% in many different locations around the target chamber. 01:10:03.572 --> 01:10:04.280 align:middle line:90% Pass that around. 01:10:04.280 --> 01:10:07.200 align:middle line:90% 01:10:07.200 --> 01:10:09.360 align:middle line:84% It's a small 5-centimeter round packet. 01:10:09.360 --> 01:10:11.950 align:middle line:84% So you really can get it in many locations. 01:10:11.950 --> 01:10:15.960 align:middle line:84% And this is also the detector material that's used for MRS, 01:10:15.960 --> 01:10:20.340 align:middle line:84% as we talked about before, CR-39 plastic. 01:10:20.340 --> 01:10:22.770 align:middle line:84% So the wedge range filter spectrometer 01:10:22.770 --> 01:10:25.388 align:middle line:84% is one example that you can see here, too. 01:10:25.388 --> 01:10:27.180 align:middle line:84% We also have charged-particle spectrometers 01:10:27.180 --> 01:10:29.430 align:middle line:84% which are very similar to MRS. It's 01:10:29.430 --> 01:10:32.747 align:middle line:84% a magnet outside of the target chamber wall. 01:10:32.747 --> 01:10:34.830 align:middle line:84% The difference is we don't have a conversion coil, 01:10:34.830 --> 01:10:36.270 align:middle line:84% so we're just looking at charged particles 01:10:36.270 --> 01:10:37.537 align:middle line:90% directly from the implosion. 01:10:37.537 --> 01:10:39.870 align:middle line:84% And you can actually-- this is another advantage of MRS. 01:10:39.870 --> 01:10:42.240 align:middle line:84% You can also run MRS in charged-particle mode 01:10:42.240 --> 01:10:45.750 align:middle line:84% for experiments where we're not interested in the neutron 01:10:45.750 --> 01:10:46.477 align:middle line:90% spectrum. 01:10:46.477 --> 01:10:48.810 align:middle line:84% And then you can look at the charged particles that come 01:10:48.810 --> 01:10:51.100 align:middle line:90% directly from the implosion. 01:10:51.100 --> 01:10:51.600 align:middle line:90% Yeah. 01:10:51.600 --> 01:10:53.760 align:middle line:84% And this is an example of looking at that symmetry 01:10:53.760 --> 01:10:57.496 align:middle line:84% and how it can vary around the implosion. 01:10:57.496 --> 01:11:01.210 align:middle line:84% This is an insertion module on the NIF, where 01:11:01.210 --> 01:11:04.330 align:middle line:84% we can field, actually, up to six of these wedge range filter 01:11:04.330 --> 01:11:06.790 align:middle line:84% spectrometers on a single insertion module. 01:11:06.790 --> 01:11:08.920 align:middle line:84% There's four insertion modules that have 01:11:08.920 --> 01:11:11.650 align:middle line:90% capability of fielding these. 01:11:11.650 --> 01:11:14.440 align:middle line:84% So you understand we can field a lot from one implosion. 01:11:14.440 --> 01:11:16.510 align:middle line:84% On OMEGA, we can field up to seven 01:11:16.510 --> 01:11:19.133 align:middle line:84% on one implosion in different directions. 01:11:19.133 --> 01:11:21.550 align:middle line:84% And in each direction, you can add a few more if you want. 01:11:21.550 --> 01:11:24.410 align:middle line:90% So a lot. 01:11:24.410 --> 01:11:24.910 align:middle line:90% Yeah. 01:11:24.910 --> 01:11:29.200 align:middle line:84% So in this case, these are fielded at 50 centimeters 01:11:29.200 --> 01:11:29.860 align:middle line:90% from implosion. 01:11:29.860 --> 01:11:31.030 align:middle line:84% These are fielded at 10 centimeters 01:11:31.030 --> 01:11:32.190 align:middle line:90% from implosion [INAUDIBLE]. 01:11:32.190 --> 01:11:34.330 align:middle line:84% So we can look in different directions. 01:11:34.330 --> 01:11:36.280 align:middle line:84% And this is actually a really old example 01:11:36.280 --> 01:11:39.935 align:middle line:84% from the paper by Johan in 2004, where he's fielded protons 01:11:39.935 --> 01:11:41.560 align:middle line:84% with [INAUDIBLE] in different locations 01:11:41.560 --> 01:11:43.630 align:middle line:84% around the OMEGA target chamber [INAUDIBLE] 01:11:43.630 --> 01:11:45.430 align:middle line:84% look in different [INAUDIBLE] spectrum. 01:11:45.430 --> 01:11:53.470 align:middle line:84% And if you think back to this, for D3, 01:11:53.470 --> 01:11:56.320 align:middle line:84% you often get these two peaks in time, a sharp peak 01:11:56.320 --> 01:11:57.430 align:middle line:90% and a compression peak. 01:11:57.430 --> 01:11:59.710 align:middle line:84% So you can also say something about the evolution 01:11:59.710 --> 01:12:00.760 align:middle line:90% of the experiment. 01:12:00.760 --> 01:12:02.390 align:middle line:84% Here, you have the time evolution. 01:12:02.390 --> 01:12:05.890 align:middle line:84% You see the small, sharp peak and the larger compression peak. 01:12:05.890 --> 01:12:08.500 align:middle line:84% And then you can also see that in the energy spectra, 01:12:08.500 --> 01:12:11.110 align:middle line:90% you have less range down-- 01:12:11.110 --> 01:12:12.950 align:middle line:84% more range down compression profiles. 01:12:12.950 --> 01:12:14.950 align:middle line:84% So you can tell the difference in aereal density 01:12:14.950 --> 01:12:17.840 align:middle line:84% between those two types of implosion. 01:12:17.840 --> 01:12:18.590 align:middle line:90% It's kind of neat. 01:12:18.590 --> 01:12:21.320 align:middle line:90% 01:12:21.320 --> 01:12:21.820 align:middle line:90% OK. 01:12:21.820 --> 01:12:23.690 align:middle line:84% I feel like I'm running out of time, so I've got to speed up. 01:12:23.690 --> 01:12:25.232 align:middle line:84% We already talked about image plates, 01:12:25.232 --> 01:12:26.780 align:middle line:84% so don't need to talk about that. 01:12:26.780 --> 01:12:29.450 align:middle line:90% CR-39, I kind of touched on. 01:12:29.450 --> 01:12:30.910 align:middle line:84% This is an example of what it can 01:12:30.910 --> 01:12:33.550 align:middle line:84% look like after we've etched it in sodium hydroxide 01:12:33.550 --> 01:12:36.520 align:middle line:84% at 80 degrees Celsius for of order hours. 01:12:36.520 --> 01:12:39.700 align:middle line:84% If we put it on one of these microscopes, step over, 01:12:39.700 --> 01:12:45.610 align:middle line:84% and take pictures for roughly 400-micron frames, 01:12:45.610 --> 01:12:50.230 align:middle line:84% the microscope automatically picks up tracks which are due 01:12:50.230 --> 01:12:52.240 align:middle line:84% to particles interacting in the CR-39, 01:12:52.240 --> 01:12:55.750 align:middle line:84% and records their roundness or eccentricity and the track size. 01:12:55.750 --> 01:12:58.330 align:middle line:84% And then we use that to reconstruct 01:12:58.330 --> 01:13:03.650 align:middle line:84% whatever information they wanted from that diagnostic. 01:13:03.650 --> 01:13:04.150 align:middle line:90% OK. 01:13:04.150 --> 01:13:08.520 align:middle line:84% So then, spend a few minutes on reaction-rate history. 01:13:08.520 --> 01:13:10.330 align:middle line:84% So there's a number of ways to do this. 01:13:10.330 --> 01:13:13.110 align:middle line:84% And again, so we're looking at really short burn, 01:13:13.110 --> 01:13:15.270 align:middle line:90% order of 100 picoseconds. 01:13:15.270 --> 01:13:17.640 align:middle line:84% We can field a plastic scintillator really close 01:13:17.640 --> 01:13:20.100 align:middle line:84% to the implosion and combine it with the streak camera 01:13:20.100 --> 01:13:22.890 align:middle line:84% to measure their reaction-rate history. 01:13:22.890 --> 01:13:24.360 align:middle line:90% This is done at OMEGA. 01:13:24.360 --> 01:13:28.060 align:middle line:84% So this picture is of the OMEGA target chamber. 01:13:28.060 --> 01:13:29.410 align:middle line:90% This is the laser. 01:13:29.410 --> 01:13:31.570 align:middle line:84% So this is not part of the diagnostic. 01:13:31.570 --> 01:13:34.960 align:middle line:84% This is how we drive the actual implosion. 01:13:34.960 --> 01:13:37.310 align:middle line:84% This is what the detector will look like. 01:13:37.310 --> 01:13:39.460 align:middle line:84% So it will be fairly close to the target chamber. 01:13:39.460 --> 01:13:41.260 align:middle line:84% There is the plastic scintillator. 01:13:41.260 --> 01:13:43.960 align:middle line:84% The light from the scintillator will 01:13:43.960 --> 01:13:48.370 align:middle line:84% be coupled through an optical light path [INAUDIBLE] camera 01:13:48.370 --> 01:13:50.090 align:middle line:90% to record a streak image. 01:13:50.090 --> 01:13:54.010 align:middle line:84% And this is where the burn history is encoded. 01:13:54.010 --> 01:13:56.410 align:middle line:84% And that scintillator will have a rise time of about 20 01:13:56.410 --> 01:13:59.770 align:middle line:84% picoseconds but a fall time of 1 and 1/2 nanoseconds. 01:13:59.770 --> 01:14:02.320 align:middle line:84% So the information, really, is encoded in the rising 01:14:02.320 --> 01:14:03.340 align:middle line:90% edge of the signal. 01:14:03.340 --> 01:14:04.750 align:middle line:90% So we have to unfold it. 01:14:04.750 --> 01:14:07.180 align:middle line:84% But when you do that, you can get the burn history 01:14:07.180 --> 01:14:10.280 align:middle line:84% as a function of time for [INAUDIBLE] compression. 01:14:10.280 --> 01:14:13.090 align:middle line:84% And this is used a lot for neutrons on OMEGA 01:14:13.090 --> 01:14:16.340 align:middle line:84% in the neutron temporal diagnostic. 01:14:16.340 --> 01:14:18.430 align:middle line:84% There's also the particle temporary diagnostic 01:14:18.430 --> 01:14:22.030 align:middle line:84% or the particle and X-ray temporal diagnostic-- similar 01:14:22.030 --> 01:14:24.970 align:middle line:84% concept, where you can tweak that scintillator 01:14:24.970 --> 01:14:28.450 align:middle line:84% setup in the center to have a number of different channels, 01:14:28.450 --> 01:14:30.050 align:middle line:84% some of them optimized for X-rays, 01:14:30.050 --> 01:14:32.383 align:middle line:84% some optimized for protons, some optimized for neutrons, 01:14:32.383 --> 01:14:35.300 align:middle line:84% depending on how you filter them and what neutron density focus 01:14:35.300 --> 01:14:37.895 align:middle line:84% you put behind [INAUDIBLE] on the streak camera 01:14:37.895 --> 01:14:39.907 align:middle line:90% and reconstruct it after. 01:14:39.907 --> 01:14:41.990 align:middle line:84% So that's actually a really neat diagnostic that's 01:14:41.990 --> 01:14:44.150 align:middle line:90% useful for a lot of things. 01:14:44.150 --> 01:14:46.700 align:middle line:84% I told you, promised you, early on that we'd get back 01:14:46.700 --> 01:14:49.520 align:middle line:90% to what we used to gammas for. 01:14:49.520 --> 01:14:52.370 align:middle line:84% So one cool thing about the gammas 01:14:52.370 --> 01:14:55.310 align:middle line:84% is they don't have the same time dispersion that neutrons do. 01:14:55.310 --> 01:14:57.890 align:middle line:84% So the neutrons, when they're emitted from target chamber 01:14:57.890 --> 01:15:00.320 align:middle line:84% center, they're going to disperse 01:15:00.320 --> 01:15:03.440 align:middle line:84% in time, which is really why we can use just the neutron time 01:15:03.440 --> 01:15:05.730 align:middle line:84% dispersion for neutron time-of-flight. 01:15:05.730 --> 01:15:08.390 align:middle line:84% So if you put the nTOF detector 20 meters away, look 01:15:08.390 --> 01:15:10.850 align:middle line:84% at the neutrons, we measure the energy spectrum, not 01:15:10.850 --> 01:15:12.980 align:middle line:90% the emission history. 01:15:12.980 --> 01:15:15.570 align:middle line:84% For the gammas, they don't disperse in time, 01:15:15.570 --> 01:15:19.520 align:middle line:84% so we can have a gamma detector relatively far away 01:15:19.520 --> 01:15:21.870 align:middle line:84% and we still retain that time history. 01:15:21.870 --> 01:15:23.180 align:middle line:90% So that's the cool part. 01:15:23.180 --> 01:15:25.625 align:middle line:84% We have the lower probability for getting gammas. 01:15:25.625 --> 01:15:29.570 align:middle line:84% I think we saw the branching ratio is about 10 to the minus 5 01:15:29.570 --> 01:15:30.650 align:middle line:90% of the neutrons. 01:15:30.650 --> 01:15:32.660 align:middle line:84% But there is enough of them to count. 01:15:32.660 --> 01:15:34.310 align:middle line:90% And by counting the gammas-- 01:15:34.310 --> 01:15:38.930 align:middle line:84% in this example, we're using the gamma reaction history detector, 01:15:38.930 --> 01:15:43.695 align:middle line:84% which is based on converter gamma rays that 01:15:43.695 --> 01:15:44.820 align:middle line:90% are converted to electrons. 01:15:44.820 --> 01:15:48.180 align:middle line:84% And electrons generate Cherenkov light in this gas cell, 01:15:48.180 --> 01:15:51.340 align:middle line:84% and then it's detected as a function of time. 01:15:51.340 --> 01:15:54.720 align:middle line:84% And that's how you infer the bank time or burn history. 01:15:54.720 --> 01:15:56.550 align:middle line:84% You get both from this measurement. 01:15:56.550 --> 01:15:59.820 align:middle line:84% This is what this detector looks like on OMEGA, 01:15:59.820 --> 01:16:01.620 align:middle line:84% and this is what it looks like on the NIF. 01:16:01.620 --> 01:16:05.290 align:middle line:84% And on the NIF, there are four different channels, 01:16:05.290 --> 01:16:07.770 align:middle line:84% which you can vary in gas pressure set at different gamma 01:16:07.770 --> 01:16:10.212 align:middle line:90% detection threshold. 01:16:10.212 --> 01:16:11.670 align:middle line:84% You don't get spectral information, 01:16:11.670 --> 01:16:14.003 align:middle line:84% but you can set a threshold and then compare the results 01:16:14.003 --> 01:16:15.900 align:middle line:90% from the four. 01:16:15.900 --> 01:16:19.540 align:middle line:84% And actually, it even made it into a movie, this detector. 01:16:19.540 --> 01:16:23.505 align:middle line:84% This is the gamma reaction history detector. 01:16:23.505 --> 01:16:25.130 align:middle line:84% Hans Hartmann, who built this detector, 01:16:25.130 --> 01:16:27.380 align:middle line:84% was really proud to be able to take his kids to this movie 01:16:27.380 --> 01:16:28.308 align:middle line:90% at the movie theater. 01:16:28.308 --> 01:16:29.742 align:middle line:90% [LAUGHTER] 01:16:29.742 --> 01:16:32.000 align:middle line:90% 01:16:32.000 --> 01:16:32.500 align:middle line:90% OK. 01:16:32.500 --> 01:16:34.300 align:middle line:84% So coming back to magnetic confinement fusion, 01:16:34.300 --> 01:16:36.730 align:middle line:84% again, here we typically use fission chambers to measure 01:16:36.730 --> 01:16:37.945 align:middle line:90% the nuclear reaction rate. 01:16:37.945 --> 01:16:40.980 align:middle line:90% 01:16:40.980 --> 01:16:45.390 align:middle line:84% And the way this works is you have the fissile material, 01:16:45.390 --> 01:16:47.850 align:middle line:84% you get the fission products going into the fuel gas. 01:16:47.850 --> 01:16:51.870 align:middle line:84% They ionize-- or, sorry-- yeah, they ionize the fuel gas, 01:16:51.870 --> 01:16:54.810 align:middle line:84% and then you get an electric pulse that goes out. 01:16:54.810 --> 01:16:56.800 align:middle line:84% And you measure that as a function of time. 01:16:56.800 --> 01:16:59.940 align:middle line:84% And here again, you need MCP model 01:16:59.940 --> 01:17:02.790 align:middle line:84% in order to determine what your measured signal actually 01:17:02.790 --> 01:17:04.120 align:middle line:90% means in terms of nutrition. 01:17:04.120 --> 01:17:06.065 align:middle line:84% These are often also in-situ calibrated, 01:17:06.065 --> 01:17:08.190 align:middle line:84% where you move the source around inside the chamber 01:17:08.190 --> 01:17:10.835 align:middle line:84% and see what the signal looks like on efficient chambers 01:17:10.835 --> 01:17:11.460 align:middle line:90% on the outside. 01:17:11.460 --> 01:17:14.360 align:middle line:90% 01:17:14.360 --> 01:17:14.990 align:middle line:90% OK. 01:17:14.990 --> 01:17:17.430 align:middle line:84% And I think have five more minutes, Jack, right? 01:17:17.430 --> 01:17:17.760 align:middle line:90% PROFESSOR: Go for it. 01:17:17.760 --> 01:17:18.920 align:middle line:84% MARIA GATU JOHNSON: So we'll take a few minutes 01:17:18.920 --> 01:17:21.770 align:middle line:84% on the impact of nuclear measurements on the ICF program 01:17:21.770 --> 01:17:24.200 align:middle line:90% at the NIF. 01:17:24.200 --> 01:17:26.700 align:middle line:84% And I think we've really touched on this throughout the talk 01:17:26.700 --> 01:17:27.360 align:middle line:90% today, right? 01:17:27.360 --> 01:17:30.030 align:middle line:84% The nuclear data have been essential for guiding 01:17:30.030 --> 01:17:31.710 align:middle line:84% the initial experiments to ignition. 01:17:31.710 --> 01:17:36.060 align:middle line:84% This is the time axis of the yield from the experiments 01:17:36.060 --> 01:17:39.905 align:middle line:90% from 2010 through now to 2024. 01:17:39.905 --> 01:17:43.240 align:middle line:84% And you can see that this is a logarithmic scale. 01:17:43.240 --> 01:17:46.190 align:middle line:84% It's obviously increased a lot over that time frame. 01:17:46.190 --> 01:17:49.040 align:middle line:84% And MRS has been part of it from the beginning. 01:17:49.040 --> 01:17:53.530 align:middle line:84% I started here at MIT in August 2010. 01:17:53.530 --> 01:17:59.690 align:middle line:84% I think the first data from the NIF came back from MRS a week-- 01:17:59.690 --> 01:18:02.090 align:middle line:90% two weeks after I started. 01:18:02.090 --> 01:18:04.400 align:middle line:84% They shipped it back in this huge moon 01:18:04.400 --> 01:18:05.670 align:middle line:90% lander looking container. 01:18:05.670 --> 01:18:09.920 align:middle line:84% It was, like, octagonal box with lots of cool packs 01:18:09.920 --> 01:18:11.850 align:middle line:90% to keep this [INAUDIBLE] cold. 01:18:11.850 --> 01:18:15.440 align:middle line:84% And we had to work day and night to etch and scan it and turn it 01:18:15.440 --> 01:18:15.950 align:middle line:90% around. 01:18:15.950 --> 01:18:18.680 align:middle line:84% And that's when we're at this yield level, right? 01:18:18.680 --> 01:18:21.710 align:middle line:90% Not registering on the scale. 01:18:21.710 --> 01:18:26.310 align:middle line:84% And then we've been working our way through up to the regions 01:18:26.310 --> 01:18:30.330 align:middle line:84% where we actually have target gain. 01:18:30.330 --> 01:18:32.330 align:middle line:84% And we've looked at many of these diagnostics 01:18:32.330 --> 01:18:34.850 align:middle line:84% today that have been essential for [INAUDIBLE] experiments 01:18:34.850 --> 01:18:36.080 align:middle line:90% to ignition. 01:18:36.080 --> 01:18:39.260 align:middle line:84% We looked at how we get ion temperature, hotspot velocity, 01:18:39.260 --> 01:18:43.470 align:middle line:84% fuel density or aereal density, and yield from the neutron 01:18:43.470 --> 01:18:44.630 align:middle line:90% spectrometers. 01:18:44.630 --> 01:18:46.610 align:middle line:84% We looked at how we get the burn width and bang 01:18:46.610 --> 01:18:49.310 align:middle line:84% time from the gamma reaction in-situ detector, which is 01:18:49.310 --> 01:18:52.280 align:middle line:90% related to the confining time. 01:18:52.280 --> 01:18:56.700 align:middle line:84% We also get neutron yield from the activation detectors 01:18:56.700 --> 01:18:59.420 align:middle line:84% as well as the map of the fuel uniformity 01:18:59.420 --> 01:19:03.110 align:middle line:84% from the real-time activation detectors. 01:19:03.110 --> 01:19:06.090 align:middle line:84% And we use neutron images to get the hotspot and fuel shield 01:19:06.090 --> 01:19:06.590 align:middle line:90% shape. 01:19:06.590 --> 01:19:10.640 align:middle line:84% And really in particular, these two 01:19:10.640 --> 01:19:13.610 align:middle line:84% have been essential for identifying those asymmetries. 01:19:13.610 --> 01:19:17.090 align:middle line:84% And seeds to asymmetries have been really hard 01:19:17.090 --> 01:19:19.400 align:middle line:84% to eliminate along the way to get there. 01:19:19.400 --> 01:19:23.100 align:middle line:90% 01:19:23.100 --> 01:19:25.470 align:middle line:90% OK. 01:19:25.470 --> 01:19:29.670 align:middle line:84% This is an example that Johan put together two years ago. 01:19:29.670 --> 01:19:32.890 align:middle line:84% On August 8, 2021, an implosion experiment 01:19:32.890 --> 01:19:36.810 align:middle line:84% at the NIF ignited and generated a then record neutron 01:19:36.810 --> 01:19:41.610 align:middle line:84% yield of 4.5 10 to the 17 1.35 megajoules. 01:19:41.610 --> 01:19:45.440 align:middle line:84% This is the MRS spectrum from that particular experiment. 01:19:45.440 --> 01:19:48.660 align:middle line:84% We were so excited about that experiment, 01:19:48.660 --> 01:19:52.110 align:middle line:84% which really, internally in the community, that was ignition. 01:19:52.110 --> 01:19:54.960 align:middle line:84% And I'll explain why in the next slide. 01:19:54.960 --> 01:19:57.480 align:middle line:84% But so this explains what I was talking about before. 01:19:57.480 --> 01:20:00.040 align:middle line:84% We have a model neutron energy spectrum, 01:20:00.040 --> 01:20:02.670 align:middle line:84% which is a Gaussian with a width governed by the ion 01:20:02.670 --> 01:20:07.710 align:middle line:84% temperature, the mean energy determined by the birth energy 01:20:07.710 --> 01:20:10.472 align:middle line:84% plus the peak shift, which is related to the velocity. 01:20:10.472 --> 01:20:12.180 align:middle line:84% And then we have this component, which is 01:20:12.180 --> 01:20:13.860 align:middle line:90% related to the aereal density. 01:20:13.860 --> 01:20:16.290 align:middle line:84% We vary those parameters to fit into our mesh 01:20:16.290 --> 01:20:17.940 align:middle line:84% and reconfigure an energy spectrum, 01:20:17.940 --> 01:20:20.490 align:middle line:84% and then we get a best fit neutron energy spectrum which 01:20:20.490 --> 01:20:24.740 align:middle line:90% explains what we actually had. 01:20:24.740 --> 01:20:26.115 align:middle line:84% And so if we look, in particular, 01:20:26.115 --> 01:20:30.120 align:middle line:84% at this implosion from 210808, many 01:20:30.120 --> 01:20:32.490 align:middle line:84% of the key nuclear observables point to this implosion 01:20:32.490 --> 01:20:35.160 align:middle line:84% being in a fundamentally new regime. 01:20:35.160 --> 01:20:37.200 align:middle line:84% We saw how the ion temperature took off. 01:20:37.200 --> 01:20:40.500 align:middle line:84% Earlier implosion under the same campaign had 5 keV. 01:20:40.500 --> 01:20:44.850 align:middle line:84% Now we measured neutron average ion temperature 10 keV-- 01:20:44.850 --> 01:20:46.830 align:middle line:90% a dramatic step up. 01:20:46.830 --> 01:20:52.580 align:middle line:84% We saw how-- the burn history is a little bit hard to see, 01:20:52.580 --> 01:20:59.010 align:middle line:84% but what happened actually is the burn history peaked later 01:20:59.010 --> 01:21:01.650 align:middle line:90% and got narrower. 01:21:01.650 --> 01:21:07.030 align:middle line:84% And what this is saying is that the yield took off 01:21:07.030 --> 01:21:08.350 align:middle line:90% during compression. 01:21:08.350 --> 01:21:13.120 align:middle line:84% So where the yield would have previously tanked, 01:21:13.120 --> 01:21:16.860 align:middle line:84% you start having it climb more and more instead. 01:21:16.860 --> 01:21:18.860 align:middle line:84% And then it becomes a really narrow burn 01:21:18.860 --> 01:21:22.640 align:middle line:84% because it's burning on as the explosion is exploding 01:21:22.640 --> 01:21:24.170 align:middle line:84% rather than as you're compressing. 01:21:24.170 --> 01:21:27.270 align:middle line:84% And that, you can see in the neutron images as well. 01:21:27.270 --> 01:21:29.930 align:middle line:84% These are neutron images and as well as one 01:21:29.930 --> 01:21:33.470 align:middle line:84% X-ray image on the top row from two predecessor implosions. 01:21:33.470 --> 01:21:36.200 align:middle line:84% This one, you can see how it gets a lot bigger. 01:21:36.200 --> 01:21:40.890 align:middle line:84% And this is, again, because it's going on the expansion. 01:21:40.890 --> 01:21:41.390 align:middle line:90% Yeah. 01:21:41.390 --> 01:21:43.220 align:middle line:90% And then the other one-- 01:21:43.220 --> 01:21:45.860 align:middle line:84% well, you're actually measuring-- 01:21:45.860 --> 01:21:49.220 align:middle line:84% this is not the best spot to show it, but what we're finding 01:21:49.220 --> 01:21:52.980 align:middle line:84% is we're actually measuring a lower down-scatter ratio. 01:21:52.980 --> 01:21:57.172 align:middle line:84% And the reason for that is we're now probing-- 01:21:57.172 --> 01:21:59.330 align:middle line:84% the density ratio that we're measuring 01:21:59.330 --> 01:22:02.120 align:middle line:84% is probing the timing the implosion 01:22:02.120 --> 01:22:03.560 align:middle line:90% after peak compression. 01:22:03.560 --> 01:22:07.070 align:middle line:84% So even though the actual down-scatter ratio-- 01:22:07.070 --> 01:22:09.188 align:middle line:84% the actual compression is the same, 01:22:09.188 --> 01:22:10.730 align:middle line:84% we're seeing fewer scattered neutrons 01:22:10.730 --> 01:22:14.310 align:middle line:84% because the peak compression is before the probing. 01:22:14.310 --> 01:22:15.185 align:middle line:90% Does that make sense? 01:22:15.185 --> 01:22:18.750 align:middle line:90% 01:22:18.750 --> 01:22:20.460 align:middle line:90% OK. 01:22:20.460 --> 01:22:22.740 align:middle line:84% And yeah, this is just another illustration 01:22:22.740 --> 01:22:25.260 align:middle line:84% of the same point, where you really see 01:22:25.260 --> 01:22:27.420 align:middle line:90% the temperature climb or jump. 01:22:27.420 --> 01:22:30.770 align:middle line:84% This is the fusion yield on the y-axis. 01:22:30.770 --> 01:22:34.860 align:middle line:84% This is an inferred hotspot mass and hotspot energy, also jumped 01:22:34.860 --> 01:22:38.070 align:middle line:90% for this one implosion. 01:22:38.070 --> 01:22:39.750 align:middle line:84% Neutron radius increased and burn 01:22:39.750 --> 01:22:44.910 align:middle line:84% rate decreased, really showing that we're in a new regime. 01:22:44.910 --> 01:22:50.590 align:middle line:84% And that was this one couple years ago. 01:22:50.590 --> 01:22:53.280 align:middle line:84% So definitely done some better ones since then. 01:22:53.280 --> 01:22:55.620 align:middle line:84% And there's another one from October 29 01:22:55.620 --> 01:22:57.210 align:middle line:84% that's not yet on this chart, too, 01:22:57.210 --> 01:22:59.730 align:middle line:84% which is the second best performing 01:22:59.730 --> 01:23:03.100 align:middle line:84% ever, so falls right between these two. 01:23:03.100 --> 01:23:09.830 align:middle line:84% And we're at 4 with gain over 1 at this point. 01:23:09.830 --> 01:23:12.928 align:middle line:84% OK, I think that's all I had for today. 01:23:12.928 --> 01:23:14.220 align:middle line:90% PROFESSOR: Thank you very much. 01:23:14.220 --> 01:23:20.420 align:middle line:90% 01:23:20.420 --> 01:23:22.428 align:middle line:90% Any other last questions? 01:23:22.428 --> 01:23:23.470 align:middle line:90% MARIA GATU JOHNSON: Yeah? 01:23:23.470 --> 01:23:25.880 align:middle line:84% AUDIENCE: What's next to try to go even higher on the gain? 01:23:25.880 --> 01:23:27.380 align:middle line:84% Because I think a lot of the changes 01:23:27.380 --> 01:23:29.205 align:middle line:90% were capsule quality, et cetera. 01:23:29.205 --> 01:23:30.580 align:middle line:84% And is there anything that you're 01:23:30.580 --> 01:23:33.340 align:middle line:84% seeing in your new neutron data from this new regime that's 01:23:33.340 --> 01:23:37.790 align:middle line:90% guiding further changes? 01:23:37.790 --> 01:23:40.970 align:middle line:84% MARIA GATU JOHNSON: Good question. 01:23:40.970 --> 01:23:44.170 align:middle line:84% I don't think there's anything super obvious right now. 01:23:44.170 --> 01:23:48.480 align:middle line:90% 01:23:48.480 --> 01:23:52.800 align:middle line:84% Part of it is pushing for bigger implosions, 01:23:52.800 --> 01:23:56.850 align:middle line:84% which is not directly related to the neutron data. 01:23:56.850 --> 01:23:57.810 align:middle line:90% Yeah. 01:23:57.810 --> 01:24:01.680 align:middle line:84% Yeah, no, I don't think there's any defect signatures right 01:24:01.680 --> 01:24:04.427 align:middle line:90% now that we're going after. 01:24:04.427 --> 01:24:06.010 align:middle line:84% AUDIENCE: Are there any open questions 01:24:06.010 --> 01:24:08.170 align:middle line:84% that you see in the neutron data [INAUDIBLE]? 01:24:08.170 --> 01:24:10.450 align:middle line:84% MARIA GATU JOHNSON: Yes, there's a big one. 01:24:10.450 --> 01:24:11.440 align:middle line:90% Great question. 01:24:11.440 --> 01:24:14.410 align:middle line:84% So actually, I talked a lot about peak upshifts 01:24:14.410 --> 01:24:16.310 align:middle line:84% and how we infer velocity from that. 01:24:16.310 --> 01:24:18.250 align:middle line:90% So there's two aspects to that. 01:24:18.250 --> 01:24:21.730 align:middle line:84% There is the peak shift that's different in each 01:24:21.730 --> 01:24:23.560 align:middle line:84% of the different lines of sight that's 01:24:23.560 --> 01:24:27.550 align:middle line:84% showing us in which direction the implosion's taking off in. 01:24:27.550 --> 01:24:31.090 align:middle line:84% But also turns out that there is a uniform [INAUDIBLE] that's 01:24:31.090 --> 01:24:33.520 align:middle line:84% the same in all lines of sight that's anomalous, 01:24:33.520 --> 01:24:36.550 align:middle line:84% that's not explained by the ion temperature 01:24:36.550 --> 01:24:39.070 align:middle line:84% and not explained by the direction of velocity. 01:24:39.070 --> 01:24:41.500 align:middle line:84% And right now, it looks like the only way 01:24:41.500 --> 01:24:45.130 align:middle line:84% to explain that upshift is by non-Maxwellian effects 01:24:45.130 --> 01:24:49.090 align:middle line:84% in the fuel line velocity distributions. 01:24:49.090 --> 01:24:51.550 align:middle line:84% It's not clear why those would arise. 01:24:51.550 --> 01:24:53.830 align:middle line:84% So that's definitely a big outstanding question 01:24:53.830 --> 01:24:57.460 align:middle line:84% that we're looking at, which excites me a lot. 01:24:57.460 --> 01:24:59.640 align:middle line:90% I like puzzles. 01:24:59.640 --> 01:25:25.000 align:middle line:90%