1 00:00:07,696 --> 00:00:09,810 MARKUS KLUTE: Welcome back to 871. 2 00:00:09,810 --> 00:00:13,680 So in this section of our discussion of instrumentation, 3 00:00:13,680 --> 00:00:16,079 we talk about accelerators, and I'll 4 00:00:16,079 --> 00:00:19,590 do this in a little bit of an historic way showing you 5 00:00:19,590 --> 00:00:25,750 some of the developments over the last up to 100 years. 6 00:00:25,750 --> 00:00:28,960 We use electromagnetic fields in order 7 00:00:28,960 --> 00:00:33,010 to accelerate charged particles, and so the developments 8 00:00:33,010 --> 00:00:37,030 in electromagnetic and understanding electromagnetism 9 00:00:37,030 --> 00:00:39,820 led to then the technical developments 10 00:00:39,820 --> 00:00:42,820 or the technological development of accelerators 11 00:00:42,820 --> 00:00:45,970 and the availability of devices, which 12 00:00:45,970 --> 00:00:52,460 can be used in order to accelerate or modify particles. 13 00:00:52,460 --> 00:00:55,090 And so this goes back to Maxwell and Hertz 14 00:00:55,090 --> 00:00:57,580 discovering electromagnetic waves 15 00:00:57,580 --> 00:01:01,990 towards JJ Thomson, who was able to use 16 00:01:01,990 --> 00:01:06,580 cathode rays and the classical Lorentz force 17 00:01:06,580 --> 00:01:08,910 in order to understand the electromagnetic fields. 18 00:01:12,740 --> 00:01:15,980 If we study particle accelerators, 19 00:01:15,980 --> 00:01:18,830 we can see three different historic lines-- 20 00:01:18,830 --> 00:01:22,820 direct voltage accelerators, resonant accelerators, 21 00:01:22,820 --> 00:01:24,920 and transformer accelerators, and we 22 00:01:24,920 --> 00:01:28,670 go through those three different subjects one by one. 23 00:01:28,670 --> 00:01:32,570 The energy limits of our accelerators, 24 00:01:32,570 --> 00:01:35,450 they are typically given by the maximum possible voltage 25 00:01:35,450 --> 00:01:38,910 available. 26 00:01:38,910 --> 00:01:42,750 When you think about accelerators used for colliding 27 00:01:42,750 --> 00:01:48,100 beams, it's not just the energy which is the limiting factor, 28 00:01:48,100 --> 00:01:51,630 but you also need a sufficient number of particles 29 00:01:51,630 --> 00:01:54,420 to be accelerated and brought to collisions. 30 00:01:54,420 --> 00:01:57,840 And those particles need to be in some sort of beam, 31 00:01:57,840 --> 00:02:01,860 which is narrow such that collisions are possible. 32 00:02:01,860 --> 00:02:03,840 Requirements change depending on whether or not 33 00:02:03,840 --> 00:02:07,260 you have colliding beams or fixed target experiments, 34 00:02:07,260 --> 00:02:10,169 whether or not you actually study 35 00:02:10,169 --> 00:02:13,200 lepton collisions, or hadron collisions, 36 00:02:13,200 --> 00:02:15,600 whether or not you're using secondary particles 37 00:02:15,600 --> 00:02:18,090 as the means of what you're going to learn from this. 38 00:02:18,090 --> 00:02:21,870 But the concepts are very comparable across 39 00:02:21,870 --> 00:02:24,870 individual fields of study. 40 00:02:24,870 --> 00:02:26,660 So let's start with the van der Meer-- 41 00:02:26,660 --> 00:02:28,910 Van de Graaff accelerator. 42 00:02:28,910 --> 00:02:33,950 So you basically have to be able to create large voltages, 43 00:02:33,950 --> 00:02:36,120 and for the Van de Graaff accelerator, 44 00:02:36,120 --> 00:02:38,810 it's been doing this, creating this large voltage, 45 00:02:38,810 --> 00:02:45,290 by just moving particles from on one level-- separating 46 00:02:45,290 --> 00:02:48,260 particles to create this large voltage. 47 00:02:48,260 --> 00:02:52,820 You can typically get up to megavolts and tens of megavolts 48 00:02:52,820 --> 00:02:56,960 of voltages, but you need to make sure 49 00:02:56,960 --> 00:03:00,420 that you don't enter a breakdown kind of regime. 50 00:03:00,420 --> 00:03:03,080 And so it depends on what kind of insulating materials 51 00:03:03,080 --> 00:03:03,980 you use. 52 00:03:03,980 --> 00:03:08,840 If you are using insulating gas under certain environmental 53 00:03:08,840 --> 00:03:14,120 conditions, you get up to 17.5 megavolts, which then can 54 00:03:14,120 --> 00:03:17,500 be used in order to accelerate. 55 00:03:17,500 --> 00:03:21,610 We can use the fact that you can use the electric fields twice 56 00:03:21,610 --> 00:03:26,170 in the tandem accelerators by changing 57 00:03:26,170 --> 00:03:29,110 the direction of the voltage. 58 00:03:29,110 --> 00:03:33,820 Large potential differences have been field of studies 59 00:03:33,820 --> 00:03:39,310 in the 1920s and '30s, and one not so-- 60 00:03:39,310 --> 00:03:43,300 and it's just noteworthy that this is a dangerous field. 61 00:03:43,300 --> 00:03:45,760 So Brasch and Lange, they use potential 62 00:03:45,760 --> 00:03:47,800 from lightning in the Swiss Alps, 63 00:03:47,800 --> 00:03:53,168 but this was fatal for Lange, who was electrocuted fatally 64 00:03:53,168 --> 00:03:54,085 by a lightning strike. 65 00:03:56,700 --> 00:03:58,800 So then you need to think about how can you 66 00:03:58,800 --> 00:04:01,230 make large voltages available, and how can you 67 00:04:01,230 --> 00:04:04,530 make them available for acceleration? 68 00:04:04,530 --> 00:04:08,330 Cockcroft-Walton accelerators use a sequence 69 00:04:08,330 --> 00:04:13,680 of a cascade generator in order to reuse the voltage in order 70 00:04:13,680 --> 00:04:18,450 to create a larger potential for acceleration. 71 00:04:18,450 --> 00:04:21,060 The max generator is very-- 72 00:04:21,060 --> 00:04:22,660 conceptually is very, very similar. 73 00:04:25,310 --> 00:04:27,080 Those are still used today, so we 74 00:04:27,080 --> 00:04:32,480 know why those developments are 80 or 90 years old. 75 00:04:32,480 --> 00:04:35,030 If you go to a Physics Today article from 2003, 76 00:04:35,030 --> 00:04:36,650 you see that a machine like this is 77 00:04:36,650 --> 00:04:42,500 being used in order to create an initial confinement for fusion 78 00:04:42,500 --> 00:04:46,385 reactors, and the total power is rather fascinating. 79 00:04:46,385 --> 00:04:50,600 It's four terabytes, which can be released in 100 nanoseconds 80 00:04:50,600 --> 00:04:53,840 from a larger number of those Marx generators. 81 00:04:56,460 --> 00:04:59,490 In modern particle physics accelerators, 82 00:04:59,490 --> 00:05:02,670 we use resonant acceleration quite a lot, 83 00:05:02,670 --> 00:05:04,920 and the idea is really like it's shown in this picture 84 00:05:04,920 --> 00:05:08,100 here, that the charged particles, 85 00:05:08,100 --> 00:05:10,350 they're kind of being accelerated on a wave. 86 00:05:10,350 --> 00:05:13,380 So basically, they're surfing on electromagnetic waves. 87 00:05:13,380 --> 00:05:14,640 And this can be seen here. 88 00:05:14,640 --> 00:05:17,390 You just place them correctly in your waveform 89 00:05:17,390 --> 00:05:19,110 on a specific point, and then they 90 00:05:19,110 --> 00:05:23,320 can be accelerated over some distance. 91 00:05:23,320 --> 00:05:26,410 So the key point here is that you 92 00:05:26,410 --> 00:05:31,750 have a proper or correct phase relation to the accelerating 93 00:05:31,750 --> 00:05:34,570 voltage, and the set up can be varying. 94 00:05:34,570 --> 00:05:36,490 And historically, there's various attempts 95 00:05:36,490 --> 00:05:38,760 to do this in an optimal way. 96 00:05:41,400 --> 00:05:44,610 The first one is the cyclotron, which 97 00:05:44,610 --> 00:05:49,260 has a static magnetic field, and in each turn, 98 00:05:49,260 --> 00:05:51,450 your particles are being injected, 99 00:05:51,450 --> 00:05:54,000 and then in each turn, your particle's 100 00:05:54,000 --> 00:05:55,800 getting a kick here and a kick here. 101 00:05:55,800 --> 00:05:59,220 And because their velocity is increasing, 102 00:05:59,220 --> 00:06:02,010 the radius in this fixed magnetic field 103 00:06:02,010 --> 00:06:03,580 is increasing as well. 104 00:06:03,580 --> 00:06:06,210 So after some time, the particle is accelerated 105 00:06:06,210 --> 00:06:10,350 and leaves the cyclotron as a specific velocity. 106 00:06:15,750 --> 00:06:16,885 Focusing here is important. 107 00:06:16,885 --> 00:06:18,510 You don't want to just inject particles 108 00:06:18,510 --> 00:06:23,700 and then they spray all over the place, an accelerator's focus 109 00:06:23,700 --> 00:06:26,880 and having the right optics for the particle is 110 00:06:26,880 --> 00:06:31,110 a key part of the work needed. 111 00:06:31,110 --> 00:06:33,240 There's a number of techniques. 112 00:06:33,240 --> 00:06:35,500 I don't want to go into too much detail, 113 00:06:35,500 --> 00:06:38,730 but what you typically see is if you compress 114 00:06:38,730 --> 00:06:41,220 the beam in one direction, it decomposes 115 00:06:41,220 --> 00:06:42,610 in the other direction. 116 00:06:42,610 --> 00:06:46,080 And so quadruple magnets can be used in order 117 00:06:46,080 --> 00:06:52,405 to get them focusing, and use fringe field and edge 118 00:06:52,405 --> 00:06:54,480 field in order to make sure that the beam itself 119 00:06:54,480 --> 00:06:56,640 stays in a compact form. 120 00:06:56,640 --> 00:07:01,218 You can also do techniques where you have initial focusing 121 00:07:01,218 --> 00:07:03,260 in one direction and then in the other direction, 122 00:07:03,260 --> 00:07:09,320 so the result can be made smaller. 123 00:07:09,320 --> 00:07:11,990 Accelerators are not just important today 124 00:07:11,990 --> 00:07:16,520 in particle physics, but they have specifically 125 00:07:16,520 --> 00:07:18,870 found their place in medical applications, 126 00:07:18,870 --> 00:07:21,410 in tumor therapy specifically. 127 00:07:21,410 --> 00:07:23,600 And the history here is very long. 128 00:07:23,600 --> 00:07:26,570 You see those initial ideas or methods 129 00:07:26,570 --> 00:07:28,220 where neutrons are used-- 130 00:07:28,220 --> 00:07:33,110 [INAUDIBLE] neutrons are used in order to treat tumors. 131 00:07:33,110 --> 00:07:35,420 We haven't discussed this in nuclear physics too much, 132 00:07:35,420 --> 00:07:39,110 but when you use ions as a radiation form, 133 00:07:39,110 --> 00:07:42,770 you can really pinpoint where energy is deposited. 134 00:07:42,770 --> 00:07:44,630 The so-called Bragg peak is used in order 135 00:07:44,630 --> 00:07:48,590 to precisely figure in a three-dimensional way 136 00:07:48,590 --> 00:07:52,850 where the energy of the ions is being deposited. 137 00:07:52,850 --> 00:07:56,290 This is in contrast to radiation therapy with photons, which 138 00:07:56,290 --> 00:08:01,670 just basically spray a larger part of the light material 139 00:08:01,670 --> 00:08:05,750 and just destroy the cancerous cells 140 00:08:05,750 --> 00:08:10,690 but also the ones which are still healthy. 141 00:08:10,690 --> 00:08:13,030 Any given large hospital nowadays 142 00:08:13,030 --> 00:08:16,450 has a small accelerator, and so there's thousands and thousands 143 00:08:16,450 --> 00:08:18,280 of those available. 144 00:08:18,280 --> 00:08:22,660 And the work and the maintenance of those is [INAUDIBLE].. 145 00:08:22,660 --> 00:08:27,760 But continuing the discussion of accelerator concepts, 146 00:08:27,760 --> 00:08:30,610 these kind of racetrack accelerators 147 00:08:30,610 --> 00:08:32,049 are quite interesting. 148 00:08:32,049 --> 00:08:34,429 You basically have a couple of fixed-- 149 00:08:34,429 --> 00:08:37,419 you have your particles being injected, 150 00:08:37,419 --> 00:08:40,360 and it's getting, like in the cyclotron, 151 00:08:40,360 --> 00:08:43,179 larger and larger kicks, and then, at some point, 152 00:08:43,179 --> 00:08:46,490 can be injected in order to do experiments. 153 00:08:46,490 --> 00:08:48,360 Again, this is not the technology 154 00:08:48,360 --> 00:08:50,990 which is not new anymore. 155 00:08:50,990 --> 00:08:55,385 MAMI is an accelerator at the University of Mainz, and it's-- 156 00:08:57,980 --> 00:09:00,890 the next generation is using-- the next generation 157 00:09:00,890 --> 00:09:04,580 of accelerators at this facility is using a similar technology. 158 00:09:09,680 --> 00:09:13,070 The question is what kind of conditions 159 00:09:13,070 --> 00:09:16,030 you have to fulfill in order to keep the particles in place, 160 00:09:16,030 --> 00:09:22,270 and here because the particle moves along, it, in each turn, 161 00:09:22,270 --> 00:09:25,150 takes more time in order to make one circulation. 162 00:09:25,150 --> 00:09:28,390 So what you want to make sure is that your phase 163 00:09:28,390 --> 00:09:32,740 and the acceleration stays in sync, 164 00:09:32,740 --> 00:09:35,470 so you want to make sure that the particular event comes 165 00:09:35,470 --> 00:09:38,860 around again, gets another kick, and it's not deaccelerated. 166 00:09:38,860 --> 00:09:42,250 And so that explains why in those machines 167 00:09:42,250 --> 00:09:43,510 the particles are bunched. 168 00:09:43,510 --> 00:09:45,730 They come in little blocks of particles 169 00:09:45,730 --> 00:09:48,550 instead of just being a continuous stream of particles, 170 00:09:48,550 --> 00:09:51,910 and you can work out the conditions necessary in order 171 00:09:51,910 --> 00:09:54,850 to fulfill the requirement that particles are 172 00:09:54,850 --> 00:09:58,740 being continuously accelerated. 173 00:09:58,740 --> 00:10:02,160 So then there's-- over the history a number 174 00:10:02,160 --> 00:10:07,200 of technologies which try to make use of the fact that when 175 00:10:07,200 --> 00:10:10,470 you accelerate, the velocity of the particles increases, 176 00:10:10,470 --> 00:10:16,710 and so initially, at a specific time, with one sequence, 177 00:10:16,710 --> 00:10:18,420 the particle gets a kick. 178 00:10:18,420 --> 00:10:22,440 And then in the next time, it's already faster. 179 00:10:22,440 --> 00:10:24,930 It travels further, so you can-- 180 00:10:24,930 --> 00:10:27,700 [INAUDIBLE] a linear accelerator structure, 181 00:10:27,700 --> 00:10:30,780 so you just increase the length of each accelerator structure 182 00:10:30,780 --> 00:10:35,010 in order to make sure that you, again, can give particles 183 00:10:35,010 --> 00:10:36,090 the necessary kick. 184 00:10:39,530 --> 00:10:42,590 Nowadays, they use cavities, and we use superconducting cavities 185 00:10:42,590 --> 00:10:44,630 in order to make them energy efficient in order 186 00:10:44,630 --> 00:10:47,300 to have large gradients. 187 00:10:47,300 --> 00:10:50,210 The general idea is, again, that you place your particle 188 00:10:50,210 --> 00:10:53,420 in here, and you place it such in your face 189 00:10:53,420 --> 00:10:57,470 in your electromagnetic field that it always 190 00:10:57,470 --> 00:10:59,990 gets a kick instead of being on the other side 191 00:10:59,990 --> 00:11:03,400 and being deaccelerated. 192 00:11:03,400 --> 00:11:07,250 Again, the Alvarez Linac is a very similar concept, 193 00:11:07,250 --> 00:11:09,010 so the advantage here is that you only 194 00:11:09,010 --> 00:11:10,960 have one power input, which then you 195 00:11:10,960 --> 00:11:15,160 couple and the walls of the machine don't dissipate energy. 196 00:11:15,160 --> 00:11:18,830 So then next, once you have an accelerator structure in place, 197 00:11:18,830 --> 00:11:21,310 you also want to make sure that the structure itself 198 00:11:21,310 --> 00:11:24,370 doesn't interfere with a beam, that the power transfer is 199 00:11:24,370 --> 00:11:28,660 as efficient as possible, such that you can get more 200 00:11:28,660 --> 00:11:31,480 for your buck. 201 00:11:31,480 --> 00:11:34,270 All right, I mentioned it a few times already, 202 00:11:34,270 --> 00:11:40,100 the fact when you have an electromagnetic wave 203 00:11:40,100 --> 00:11:42,302 of this form and you put your particle here, 204 00:11:42,302 --> 00:11:44,510 the question is what happens to these particles which 205 00:11:44,510 --> 00:11:47,390 have a slightly higher energy over these particle which 206 00:11:47,390 --> 00:11:49,320 have a slightly lower energy? 207 00:11:49,320 --> 00:11:51,230 And it turns out that this kind of wave 208 00:11:51,230 --> 00:11:56,070 has a self-focusing kind of structure in a sense 209 00:11:56,070 --> 00:11:59,490 that the particles were a little bit behind, they 210 00:11:59,490 --> 00:12:01,400 get a little bit larger kick. 211 00:12:01,400 --> 00:12:03,150 Particles which are a little bit in front, 212 00:12:03,150 --> 00:12:04,950 they get a little bit lower kick, which 213 00:12:04,950 --> 00:12:09,890 means overall in energy you focus your bunch. 214 00:12:09,890 --> 00:12:13,330 In energy and space, you focus the bunch. 215 00:12:13,330 --> 00:12:16,430 You can go one step further using RF quadrupoles. 216 00:12:16,430 --> 00:12:18,470 Again, no details given here. 217 00:12:18,470 --> 00:12:21,650 You use this unit in order to further squeeze the beam 218 00:12:21,650 --> 00:12:25,580 and reduce the footprint in energy and space, the phase 219 00:12:25,580 --> 00:12:28,610 space your particles are occupying. 220 00:12:31,740 --> 00:12:38,510 All right, the next level here is then to use a betatron, 221 00:12:38,510 --> 00:12:44,400 and the idea of the betatron is that you change 222 00:12:44,400 --> 00:12:46,020 the magnetic field as you go. 223 00:12:46,020 --> 00:12:48,828 Instead of changing the size of the structure, 224 00:12:48,828 --> 00:12:50,370 you change the magnetic field, so you 225 00:12:50,370 --> 00:12:54,930 can use the same structure in order to confine your beams. 226 00:12:54,930 --> 00:12:57,540 And the next level to this is that you don't just 227 00:12:57,540 --> 00:12:58,410 use one magnet. 228 00:12:58,410 --> 00:13:01,660 You use many magnets, and this is done in synchrotrons, 229 00:13:01,660 --> 00:13:03,940 modern synchrotrons. 230 00:13:03,940 --> 00:13:08,910 So here, again, the large line in history, but the point 231 00:13:08,910 --> 00:13:13,530 is that when you use the same orbit for the particles, 232 00:13:13,530 --> 00:13:17,040 the way you accelerate them, your magnet structures 233 00:13:17,040 --> 00:13:19,750 can become much, much smaller. 234 00:13:19,750 --> 00:13:24,040 So you have many small magnets instead of one large magnet, 235 00:13:24,040 --> 00:13:27,680 and only one or few accelerator sections are needed. 236 00:13:27,680 --> 00:13:30,550 So the particle passes by here as being accelerated, 237 00:13:30,550 --> 00:13:35,210 and then you have magnets, of course, a link, the ring, 238 00:13:35,210 --> 00:13:40,750 which are able to change their field strength. 239 00:13:40,750 --> 00:13:42,812 Again, if you have constant field strength, 240 00:13:42,812 --> 00:13:45,020 the radius changes, but if you're modifying the field 241 00:13:45,020 --> 00:13:47,530 strength accordingly to the speed of the particle, 242 00:13:47,530 --> 00:13:52,255 you can keep particles in the same circular structure. 243 00:13:55,900 --> 00:13:57,910 More words on the focusing, again, 244 00:13:57,910 --> 00:14:03,400 if you space a magnet such that there's gradient in the fields 245 00:14:03,400 --> 00:14:04,690 between-- 246 00:14:04,690 --> 00:14:07,060 depending on the position, you can use that fact 247 00:14:07,060 --> 00:14:10,990 in order to have particles which are further out being 248 00:14:10,990 --> 00:14:12,040 bent more inwards. 249 00:14:12,040 --> 00:14:14,660 Particles which are further inwards, bend more outwards. 250 00:14:14,660 --> 00:14:16,750 This is called refocusing, and you 251 00:14:16,750 --> 00:14:19,180 can do this not just once, but twice, 252 00:14:19,180 --> 00:14:20,410 by changing the rotation. 253 00:14:20,410 --> 00:14:24,860 And that's called strong focusing. 254 00:14:24,860 --> 00:14:27,450 Synchrotrons have limitations. 255 00:14:27,450 --> 00:14:29,250 There's two which are rather important. 256 00:14:29,250 --> 00:14:32,900 The first one, the radius of the synchrotron 257 00:14:32,900 --> 00:14:35,510 is determined by the momentum of the particle 258 00:14:35,510 --> 00:14:37,380 and your magnetic field. 259 00:14:37,380 --> 00:14:40,370 So at some point, you run into technical limitations 260 00:14:40,370 --> 00:14:42,770 on the magnetic field strength. 261 00:14:42,770 --> 00:14:45,680 Modern superconducting magnets, they 262 00:14:45,680 --> 00:14:49,580 get up to in the order of eight, nine tesla. 263 00:14:49,580 --> 00:14:53,540 We are able to produce accelerator-grade magnets up 264 00:14:53,540 --> 00:14:58,100 to 14 tesla using superconducting materials. 265 00:14:58,100 --> 00:15:01,340 And so that then was a fixed plot size of your tunnel 266 00:15:01,340 --> 00:15:05,450 of your ring limits the amount of momentum you can give 267 00:15:05,450 --> 00:15:07,470 or energy you can give to your particle. 268 00:15:07,470 --> 00:15:14,450 And so for the LHC, we accelerate protons up to 75 TV 269 00:15:14,450 --> 00:15:18,860 in one beam, and we use the magnetic field of 8.4 tesla. 270 00:15:18,860 --> 00:15:21,443 So that's really the maximum the machine can actually deliver, 271 00:15:21,443 --> 00:15:23,735 and we haven't actually demonstrated that we can get up 272 00:15:23,735 --> 00:15:24,350 to this point. 273 00:15:24,350 --> 00:15:30,860 Right now the center of mass, the proton energy is 6.5 TV. 274 00:15:30,860 --> 00:15:33,710 The previous concept and construction 275 00:15:33,710 --> 00:15:36,530 had started in Texas in the United States 276 00:15:36,530 --> 00:15:40,550 in the so-called SSC tunnel, which was much, much larger, 277 00:15:40,550 --> 00:15:44,270 had 87 kilometer tunnel. 278 00:15:44,270 --> 00:15:46,230 The idea was to get protons to center 279 00:15:46,230 --> 00:15:51,050 at energies of 20 TV with magnets of 6.8 tesla. 280 00:15:53,860 --> 00:15:56,770 OK, this is one limitation, the size of your tunnel. 281 00:15:56,770 --> 00:16:01,130 The second one is when you bend a charged particle 282 00:16:01,130 --> 00:16:03,140 with the magnetic field, it radiates, 283 00:16:03,140 --> 00:16:08,080 and it radiates proportional with the energy proportion 284 00:16:08,080 --> 00:16:11,320 energy over mass to the fourth power, which 285 00:16:11,320 --> 00:16:17,190 means that you, at some point, are limited by the power you 286 00:16:17,190 --> 00:16:19,200 have to invest in the beam to even just keep it 287 00:16:19,200 --> 00:16:21,000 at a specific energy. 288 00:16:21,000 --> 00:16:27,220 So this is e over m and to the fourth power, 289 00:16:27,220 --> 00:16:31,020 and this also gives you a clue why we actually 290 00:16:31,020 --> 00:16:34,330 accelerate protons in the LHC and not electrons. 291 00:16:34,330 --> 00:16:37,630 Electron mass is to low, and this goes to the fourth power 292 00:16:37,630 --> 00:16:38,410 here. 293 00:16:38,410 --> 00:16:42,580 The [INAUDIBLE] of electrons in the LHC tunnel 294 00:16:42,580 --> 00:16:43,782 is just a limiting factor. 295 00:16:43,782 --> 00:16:46,240 At some point, you don't have enough power anymore in order 296 00:16:46,240 --> 00:16:48,310 to give that to the electrons or the particles 297 00:16:48,310 --> 00:16:49,980 in order to accelerate that. 298 00:16:53,500 --> 00:16:56,560 All right, so as I was saying initially, 299 00:16:56,560 --> 00:16:59,650 so you need focusing, you need accelerating, 300 00:16:59,650 --> 00:17:03,880 and you need all kinds of additional components 301 00:17:03,880 --> 00:17:07,750 to accelerate in order to make good colliding beams, 302 00:17:07,750 --> 00:17:12,280 and so it's much easier to just dump a beam into a fixed target 303 00:17:12,280 --> 00:17:13,780 and study what's coming out. 304 00:17:13,780 --> 00:17:18,160 So colliding beams as a source for input into particle physics 305 00:17:18,160 --> 00:17:20,599 experiments came a little bit later. 306 00:17:20,599 --> 00:17:26,260 First concepts came to fruition in Frascati in the 1960s, 307 00:17:26,260 --> 00:17:30,640 and then we had SPEAR, a electron positron collider. 308 00:17:30,640 --> 00:17:33,370 It sent off mass energy of four GeV, which then led 309 00:17:33,370 --> 00:17:36,730 to the discovery of the J/Psi. 310 00:17:36,730 --> 00:17:42,070 And then later, we had a five GeV electron positron collider, 311 00:17:42,070 --> 00:17:45,610 which was then designed for eight GeV. 312 00:17:45,610 --> 00:17:51,890 This then continued, as you know, 313 00:17:51,890 --> 00:17:55,000 to machines like [INAUDIBLE],, which 314 00:17:55,000 --> 00:17:58,990 had a center of mass energy of up to 110 GeV. 315 00:17:58,990 --> 00:18:03,780 And the LHC, the center of mass energy of design of 14 GeV. 316 00:18:03,780 --> 00:18:07,230 So the collider elements, what do you need? 317 00:18:07,230 --> 00:18:10,630 You need to inject particles, and so you 318 00:18:10,630 --> 00:18:12,550 have to have a source of electrons 319 00:18:12,550 --> 00:18:13,870 and a source of positrons. 320 00:18:13,870 --> 00:18:17,230 Producing positrons is just, technologically 321 00:18:17,230 --> 00:18:20,540 in large numbers, much more complicated than electrons. 322 00:18:20,540 --> 00:18:27,630 Here you can-- in order to get sufficient electrons, 323 00:18:27,630 --> 00:18:31,320 you need to actually produce them 324 00:18:31,320 --> 00:18:34,750 with some kind of an accelerator structure as well. 325 00:18:34,750 --> 00:18:36,540 And so then they need to be focused. 326 00:18:36,540 --> 00:18:38,370 They need to be cooled down in order 327 00:18:38,370 --> 00:18:42,730 to have them as a beam being injected in the structure. 328 00:18:42,730 --> 00:18:45,000 So you've got-- you need as additional components, 329 00:18:45,000 --> 00:18:47,550 you need your RF generators. 330 00:18:47,550 --> 00:18:51,960 You need magnets to bend the beam in and out. 331 00:18:51,960 --> 00:18:55,930 You need to have magnets in order to bend the beam around, 332 00:18:55,930 --> 00:18:57,120 so we need bending magnets. 333 00:18:57,120 --> 00:19:00,897 You need focusing magnets to keep the beam in orbit, 334 00:19:00,897 --> 00:19:02,730 and then you want to-- before you bring them 335 00:19:02,730 --> 00:19:05,520 to the collision, we want to further focus the beam such 336 00:19:05,520 --> 00:19:09,540 that you have more actual particle collisions available. 337 00:19:09,540 --> 00:19:11,070 And then you have interaction points 338 00:19:11,070 --> 00:19:13,440 where you will put your particle for the experiment. 339 00:19:17,680 --> 00:19:20,260 What's being done here in this facility 340 00:19:20,260 --> 00:19:22,960 is you inject, you accelerate, and then you 341 00:19:22,960 --> 00:19:25,690 store the beam to make sure that you can fully 342 00:19:25,690 --> 00:19:31,210 exploit the structure, so those rings are called storage rings. 343 00:19:31,210 --> 00:19:36,010 You avoid having a one kind of shot kind of mentality 344 00:19:36,010 --> 00:19:39,550 as you have, for example, in linear machine. 345 00:19:39,550 --> 00:19:41,240 Sometimes you do this in separate rings. 346 00:19:41,240 --> 00:19:43,660 Sometimes you do this in the same ring. 347 00:19:43,660 --> 00:19:46,030 It depends on the design of the machine. 348 00:19:46,030 --> 00:19:48,880 The challenges are if you have particles travel around 349 00:19:48,880 --> 00:19:53,400 for hours that they shouldn't interact with the gas, 350 00:19:53,400 --> 00:19:55,410 for example, in your accelerator structure. 351 00:19:55,410 --> 00:19:58,290 [INAUDIBLE] by a very, very good vacuum in order 352 00:19:58,290 --> 00:20:02,550 to not lose the beam as you have it stored. 353 00:20:02,550 --> 00:20:05,040 The fields of your accelerator structures 354 00:20:05,040 --> 00:20:07,350 need to be very stable, and that stable-- 355 00:20:07,350 --> 00:20:09,930 they have to be stable for many, many hours. 356 00:20:09,930 --> 00:20:12,570 That, for example, there's some requirements 357 00:20:12,570 --> 00:20:16,980 on your electric grid, for example, such 358 00:20:16,980 --> 00:20:21,600 that you have the stability and voltage which don't end up 359 00:20:21,600 --> 00:20:24,720 changing the actual field strength of your magnet 360 00:20:24,720 --> 00:20:27,930 as you go along. 361 00:20:27,930 --> 00:20:30,690 Yeah, so again, I already mentioned 362 00:20:30,690 --> 00:20:33,600 this, the further development of those machines. 363 00:20:33,600 --> 00:20:39,090 In the '80s at CERN, stochastic cooling 364 00:20:39,090 --> 00:20:44,160 was used for the first time in an antiproton machine, 365 00:20:44,160 --> 00:20:45,750 and that machine led to the discovery 366 00:20:45,750 --> 00:20:51,270 of the w and the z bosons and first really deep study 367 00:20:51,270 --> 00:20:55,770 of the weak interaction at the scale of the weak interaction. 368 00:20:55,770 --> 00:20:59,970 At the TEVATRON close to Chicago, 369 00:20:59,970 --> 00:21:01,590 protons and antiprotons were brought 370 00:21:01,590 --> 00:21:06,570 to collision at the Fermilab at the Fermi National Accelerator 371 00:21:06,570 --> 00:21:08,010 Laboratory. 372 00:21:08,010 --> 00:21:13,170 And the lab started in the late 1980s in the same tunnel 373 00:21:13,170 --> 00:21:16,650 as we find today the LHC. 374 00:21:16,650 --> 00:21:22,620 At DESY in Hamburg, HERA was used to collide electrons 375 00:21:22,620 --> 00:21:26,070 with protons, and those results led to our understanding 376 00:21:26,070 --> 00:21:27,940 of the structure of the proton. 377 00:21:27,940 --> 00:21:31,080 So you see that the reason why I show you this history 378 00:21:31,080 --> 00:21:35,910 here is that the progress we did in particle physics 379 00:21:35,910 --> 00:21:39,630 at the energy frontier, each of the energy frontiers, 380 00:21:39,630 --> 00:21:43,380 was very much tied to the progress in accelerator 381 00:21:43,380 --> 00:21:44,370 structures. 382 00:21:44,370 --> 00:21:47,790 And rightfully so, Simon van der Meer 383 00:21:47,790 --> 00:21:50,910 recieved the Nobel Prize in physics as an accelerator 384 00:21:50,910 --> 00:21:55,440 physicist for the discovery of the w and z boson. 385 00:21:55,440 --> 00:21:57,750 He was working on the machine and made 386 00:21:57,750 --> 00:22:01,080 the machine possible together with Carlo Rubbia. 387 00:22:04,896 --> 00:22:08,020 And interesting, if you look at the history of the particle 388 00:22:08,020 --> 00:22:12,400 accelerators, it's interesting to see how we may move 389 00:22:12,400 --> 00:22:13,880 the energy frontier forward. 390 00:22:13,880 --> 00:22:15,280 So what you see in this plot here 391 00:22:15,280 --> 00:22:19,470 is the available energy of the machine, and what you see here 392 00:22:19,470 --> 00:22:20,110 is line. 393 00:22:20,110 --> 00:22:22,000 And this project is called the Livingston Project. 394 00:22:22,000 --> 00:22:23,417 See the logarithmic scale, and you 395 00:22:23,417 --> 00:22:27,670 saw that for a very long time it was this logarithmic increase 396 00:22:27,670 --> 00:22:28,810 in available energy. 397 00:22:28,810 --> 00:22:30,790 So this line is now turning over. 398 00:22:30,790 --> 00:22:34,790 You're Already in 2020, and we haven't made any progress here. 399 00:22:34,790 --> 00:22:39,010 So focus here on this. 400 00:22:39,010 --> 00:22:42,540 However, interesting discussions on going somewhere-- 401 00:22:42,540 --> 00:22:47,130 going to high, going somewhere here with the next machine 402 00:22:47,130 --> 00:22:49,860 and being able to probe further higher energies. 403 00:22:49,860 --> 00:22:53,100 And the way this is proposed for proton-proton collision 404 00:22:53,100 --> 00:22:56,370 was just making a structure similar to the LHC 405 00:22:56,370 --> 00:22:58,110 but with a radius about four times 406 00:22:58,110 --> 00:23:02,190 larger, about 100 kilometers compared to the 27 407 00:23:02,190 --> 00:23:04,617 kilometers the LHC as today. 408 00:23:04,617 --> 00:23:07,200 And so you can compare this with the hadron machines, but also 409 00:23:07,200 --> 00:23:10,480 the electron machines, and also on the electron machines, 410 00:23:10,480 --> 00:23:15,540 this trend is not as pronounced as for the proton machines. 411 00:23:15,540 --> 00:23:18,790 But basically, here, the highest energy electron positron 412 00:23:18,790 --> 00:23:21,690 collider [INAUDIBLE] has just been decommissioned 413 00:23:21,690 --> 00:23:24,420 at the end of the last century, and we are thinking 414 00:23:24,420 --> 00:23:26,910 about the next machine. 415 00:23:26,910 --> 00:23:31,780 Sometimes you see those acronyms as a linear machine, 416 00:23:31,780 --> 00:23:35,680 international linear collider or future circular collider. 417 00:23:35,680 --> 00:23:37,395 It's electron and positron collisions, 418 00:23:37,395 --> 00:23:38,770 which would be hosted in the very 419 00:23:38,770 --> 00:23:42,790 same tunnel as this machine, which is called FCCPP or HH. 420 00:23:46,610 --> 00:23:51,340 HH was 100 kilometer circumference.