WEBVTT 1 00:00:03.100 --> 00:00:04.330 STFC-RAL-CR03-RAL-R61-2.01: Okay. 2 00:00:06.550 --> 00:00:13.939 STFC-RAL-CR03-RAL-R61-2.01: Okay, everyone, welcome to the seminar. Let me introduce our speaker, Professor Simon Pooker. 3 00:00:14.200 --> 00:00:32.140 STFC-RAL-CR03-RAL-R61-2.01: It is here in Oxford, where he did his undergraduate and doctoral research on short wavelength lasers under the supervision of Professor Kevin Webb. After two years at Stanford University, he returned in 1996 to Oxford. 4 00:00:32.390 --> 00:00:36.699 STFC-RAL-CR03-RAL-R61-2.01: as a Royal Society University Research Fellow. 5 00:00:36.920 --> 00:00:55.950 STFC-RAL-CR03-RAL-R61-2.01: And in 2003, was appointed to a university lectureship and to a tutorial fellowship at Martin. He was head of the sub-department of Atomic and Laser Physics between 2019 and 2024. 6 00:00:56.400 --> 00:01:15.240 STFC-RAL-CR03-RAL-R61-2.01: Simon's group in Oxford has worked on a range of topics, including string ultraviolet lasers, high-intensity waveguides, and most recently, on laser-driven plasma accelerators. To date, Simon has supervised 26 PhD students. 7 00:01:15.670 --> 00:01:30.739 STFC-RAL-CR03-RAL-R61-2.01: He's a regular user of the high power laser facilities here at RAL, mainly the Astra Gemini laser, but he has also undertaken experiments in Athens, Berkeley, Paris, Munich, and CERN. 8 00:01:30.980 --> 00:01:40.359 STFC-RAL-CR03-RAL-R61-2.01: Simon has a fellowship in Optica, which is the Form Optical Society of America, and the UK Institute of Physics. 9 00:01:40.550 --> 00:01:57.850 STFC-RAL-CR03-RAL-R61-2.01: He has received also numerous awards, among them, in 2010, he was awarded the APS John Dawson Prize for Excellence in Plasma Physics, and in 2020, the IOP Cecilia Paintoposhkin Medal and Prize. 10 00:01:58.170 --> 00:02:01.469 STFC-RAL-CR03-RAL-R61-2.01: So welcome me to welcome you. 11 00:02:06.200 --> 00:02:09.840 STFC-RAL-CR03-RAL-R61-2.01: Thank you very much, and thank you for giving me the chance to 12 00:02:10.030 --> 00:02:22.099 STFC-RAL-CR03-RAL-R61-2.01: talk to you today about progress towards overgrade laser plasma accelerators. I can see several people in the audience know more about this than I do, which is a little bit concerning. 13 00:02:22.240 --> 00:02:24.489 STFC-RAL-CR03-RAL-R61-2.01: But I'll do my best. 14 00:02:24.820 --> 00:02:37.529 STFC-RAL-CR03-RAL-R61-2.01: And I hope the meaning of the very nice picture you can see at the bottom, which is drawn by Roman Balchak's wife, Anna. I hope that will become clear during the talk. 15 00:02:38.450 --> 00:02:40.130 STFC-RAL-CR03-RAL-R61-2.01: Okay, so let me first thank… 16 00:02:40.290 --> 00:02:58.049 STFC-RAL-CR03-RAL-R61-2.01: with current and past members of my group. This is a sort of selection, a random selection of of them. They've done all the hard work, of course. As you just heard, I've done a lot of experiments over the years here at the Central Laser Facility, and I'd like to thank 17 00:02:58.100 --> 00:03:06.910 STFC-RAL-CR03-RAL-R61-2.01: people there who've made that possible. And we're working very closely with Stefan Karsh in Munich in this group. See some results from that. 18 00:03:07.080 --> 00:03:10.419 STFC-RAL-CR03-RAL-R61-2.01: As well, I'm finding some of the results, that show you… 19 00:03:10.530 --> 00:03:12.990 STFC-RAL-CR03-RAL-R61-2.01: in collaboration with Laura Coleman, that group. 20 00:03:13.110 --> 00:03:13.840 STFC-RAL-CR03-RAL-R61-2.01: Okay. 21 00:03:14.710 --> 00:03:16.869 STFC-RAL-CR03-RAL-R61-2.01: So, by way of motivation. 22 00:03:16.930 --> 00:03:31.300 STFC-RAL-CR03-RAL-R61-2.01: And these these machines will be familiar to most of you, I guess. Certainly the one in the top left. I've forgotten. I've got my bearings, but it's over there or there, or maybe over there. But anyhow, that's the 23 00:03:31.320 --> 00:03:37.429 STFC-RAL-CR03-RAL-R61-2.01: accelerates electrons to about 3 Gev. And then translates into sort of mainly extra beams. 24 00:03:37.500 --> 00:03:42.459 STFC-RAL-CR03-RAL-R61-2.01: via insertion devices and just using the single door radiation as well. 25 00:03:43.110 --> 00:03:56.080 STFC-RAL-CR03-RAL-R61-2.01: So I think we're all familiar with. So that's a 27 kilometer machine, 70 UV protons, protons. And then just in the middle. Here we have the extreme 26 00:03:56.230 --> 00:04:01.480 STFC-RAL-CR03-RAL-R61-2.01: Oh, that's that's an X-ray. If you actually needed it. Daisy and both. 27 00:04:01.970 --> 00:04:08.600 STFC-RAL-CR03-RAL-R61-2.01: which is a 17 Gb. Accelerator about 3 kilometers long. 28 00:04:08.850 --> 00:04:15.499 STFC-RAL-CR03-RAL-R61-2.01: And so you can see these are not small devices, wide range of uses. 29 00:04:15.720 --> 00:04:28.029 STFC-RAL-CR03-RAL-R61-2.01: The thing which sets the scale is is the accelerating gradient that you can achieve in the radio frequency cavities which lie at the heart of this technology. So you can see a cartoon of that at the bottom. 30 00:04:28.190 --> 00:04:31.330 STFC-RAL-CR03-RAL-R61-2.01: And that grade is about 100 megavolts a meter. 31 00:04:31.970 --> 00:04:34.519 STFC-RAL-CR03-RAL-R61-2.01: roughly, it's often quite a bit less than that. 32 00:04:34.760 --> 00:04:39.370 STFC-RAL-CR03-RAL-R61-2.01: whereas stuff I'm going to talk about can reach gradients of 100 gigabytes per meter. 33 00:04:39.530 --> 00:04:43.910 STFC-RAL-CR03-RAL-R61-2.01: Okay, so it's a factor of a thousand more. Which… 34 00:04:44.120 --> 00:04:52.699 STFC-RAL-CR03-RAL-R61-2.01: If you're not sure whether a pension for a thousand is worth having, just imagine applying it to your salary. It's good things. 35 00:04:52.870 --> 00:04:58.469 STFC-RAL-CR03-RAL-R61-2.01: So this is essentially what we'll talk about. And I'm going to try and give an overview of how these things work. It will be 36 00:04:58.690 --> 00:05:07.610 STFC-RAL-CR03-RAL-R61-2.01: quite a sort of high level overview. I hope so. I don't think we're going to very much detail. If you have detailed questions, be directed towards Bob. 37 00:05:07.750 --> 00:05:17.520 STFC-RAL-CR03-RAL-R61-2.01: So I'm going to talk about the basic concept. I'll talk about some progress in, I think, more slides. I'm going to advance 20 years more in 4 slides. And then I'll talk about 38 00:05:17.830 --> 00:05:23.129 STFC-RAL-CR03-RAL-R61-2.01: something we've been involved with, which is a channel which is around 39 00:05:23.270 --> 00:05:27.400 STFC-RAL-CR03-RAL-R61-2.01: extending the the acceleration length of very good accelerators. 40 00:05:27.520 --> 00:05:39.050 STFC-RAL-CR03-RAL-R61-2.01: I'll pause to sort of give a 1 side overview of where we think we are at the moment, and then talk a little bit if I have time about increasing the repetition rates of this sort of approach. 41 00:05:40.080 --> 00:05:46.050 STFC-RAL-CR03-RAL-R61-2.01: So the, the basic idea is straightforward. So in this, in this cartoon. 42 00:05:46.320 --> 00:05:49.499 STFC-RAL-CR03-RAL-R61-2.01: The Gregory mob is a driver. 43 00:05:49.760 --> 00:05:54.259 STFC-RAL-CR03-RAL-R61-2.01: It could be an intense laser pulse, or it could be a particle beam. 44 00:05:54.690 --> 00:05:57.920 STFC-RAL-CR03-RAL-R61-2.01: And it's moving through plasma, so ionized gas. 45 00:05:58.080 --> 00:06:04.860 STFC-RAL-CR03-RAL-R61-2.01: In this picture we're moving along with the driver. So fresh plasma is going to come in from the right hand side. 46 00:06:05.570 --> 00:06:11.319 STFC-RAL-CR03-RAL-R61-2.01: and the driver applies a force to the charged particles in the plasma. 47 00:06:11.700 --> 00:06:23.200 STFC-RAL-CR03-RAL-R61-2.01: It acts on both the ions and the electrons in the plasma, because the ions are more massive by 2,000 or so, the more ice don't move. So you can think of the ions just coming through, right to left. 48 00:06:23.660 --> 00:06:26.249 STFC-RAL-CR03-RAL-R61-2.01: You don't have to push away from the drivers. 49 00:06:26.370 --> 00:06:40.400 STFC-RAL-CR03-RAL-R61-2.01: Now, the force responsible for that, if it's a particle being just a human force, you can actually push a whale or something in it, and make a massive difference. But for laser polys, it's a thing called the polar derivative force, which we'll come to in a moment. 50 00:06:41.200 --> 00:06:47.639 STFC-RAL-CR03-RAL-R61-2.01: So the driver driver's job is just to push the electrons radially outwards, actually also forwards and backwards. 51 00:06:47.920 --> 00:06:55.499 STFC-RAL-CR03-RAL-R61-2.01: So these electrons are kicked out, they flow around the drive in this moving frame, see the positive ions in the network pulled in. 52 00:06:55.880 --> 00:06:57.680 STFC-RAL-CR03-RAL-R61-2.01: By the ions that are left. 53 00:06:57.920 --> 00:07:02.750 STFC-RAL-CR03-RAL-R61-2.01: Because the electrons have transverse and longitudinal momentum, they tend to overshoot, but will overshoot. 54 00:07:03.390 --> 00:07:08.159 STFC-RAL-CR03-RAL-R61-2.01: And that sets up the region of high electrical density just lying behind the driver. 55 00:07:08.530 --> 00:07:14.139 STFC-RAL-CR03-RAL-R61-2.01: At which point the electoral will be repelled from that region, and then this process repeats. 56 00:07:15.030 --> 00:07:16.640 STFC-RAL-CR03-RAL-R61-2.01: So, the… 57 00:07:17.050 --> 00:07:23.740 STFC-RAL-CR03-RAL-R61-2.01: result of this is, we get a density structure sitting behind the driver, moving along with the driver. 58 00:07:23.870 --> 00:07:30.500 STFC-RAL-CR03-RAL-R61-2.01: We've separated electrons and ions. The Gaussian field tells us there must be a field associated with that separation. 59 00:07:30.880 --> 00:07:41.289 STFC-RAL-CR03-RAL-R61-2.01: And it's this electric field in this structure, these fields here, not the field of laser, these fields here that you can use to accelerate charged particles if you can get them in there somehow. 60 00:07:42.200 --> 00:07:50.420 STFC-RAL-CR03-RAL-R61-2.01: Now, because the whole structure is moving at the speed of light, you can accelerate relativistic particles. With this approach. 61 00:07:51.010 --> 00:07:56.180 STFC-RAL-CR03-RAL-R61-2.01: So, just to put a few numbers in here… the… the natural… 62 00:07:56.530 --> 00:08:03.370 STFC-RAL-CR03-RAL-R61-2.01: Observation frequency of the plasma, as you might remember, is plasma frequency. Omega P. So we'll look here a few times. 63 00:08:03.610 --> 00:08:07.960 STFC-RAL-CR03-RAL-R61-2.01: The only thing you need to know is it goes up the square root of the natural density proposal. 64 00:08:08.610 --> 00:08:15.650 STFC-RAL-CR03-RAL-R61-2.01: That's the net phosphation period of any disturbance in plasma. So that's going to play a key role. 65 00:08:15.860 --> 00:08:24.259 STFC-RAL-CR03-RAL-R61-2.01: The maximum field you can get is called the wave breaking field, and in one minute it's given by this expression, which is 66 00:08:24.780 --> 00:08:28.329 STFC-RAL-CR03-RAL-R61-2.01: The cold, we're breaking limit, and again it goes like Omega-P. 67 00:08:29.080 --> 00:08:32.350 STFC-RAL-CR03-RAL-R61-2.01: So there's, like, a density, And. 68 00:08:32.990 --> 00:08:45.660 STFC-RAL-CR03-RAL-R61-2.01: and the the time period of this this oscillation is just set by the one over omega p. And that sets the wavelength of the distance between these regions of high identity for that scale there. 69 00:08:46.010 --> 00:08:47.720 STFC-RAL-CR03-RAL-R61-2.01: That's a good place to work with. 70 00:08:48.350 --> 00:08:53.469 STFC-RAL-CR03-RAL-R61-2.01: Now, to get an efficient excitation of this so-called Wakefield. 71 00:08:53.710 --> 00:08:58.880 STFC-RAL-CR03-RAL-R61-2.01: It's useful to have the kick supplied via the laser pulse. 72 00:08:58.980 --> 00:09:11.579 STFC-RAL-CR03-RAL-R61-2.01: appropriately time. So if you if you imagine there's going to be a kick from the front edge, we'll explain in a moment and the back edge. If if they're spaced by essentially half the passive period, then 73 00:09:11.800 --> 00:09:15.489 STFC-RAL-CR03-RAL-R61-2.01: You get a double kick onto the electrons, and you get a bit more amplitude. 74 00:09:15.720 --> 00:09:25.869 STFC-RAL-CR03-RAL-R61-2.01: So it's not a very strong resonance, but nonetheless, if there's a sort of weak resonance there that you'd like to try and hit. And what that means is you want this driver to sit inside 75 00:09:26.130 --> 00:09:30.109 STFC-RAL-CR03-RAL-R61-2.01: one personal way back. It can't be too long. 76 00:09:30.970 --> 00:09:41.419 STFC-RAL-CR03-RAL-R61-2.01: So first, st in there, and the sorts of intensities that we're going to need are around 10 to the 18 watts per square centimeter. So I'm sorry for the funny units. But that's what people use. 77 00:09:42.240 --> 00:09:50.839 STFC-RAL-CR03-RAL-R61-2.01: And that's about a joule of energy in a laser pulse, maybe 50 pentoseconds long, focused to maybe 25 microns or so. 78 00:09:50.950 --> 00:09:54.849 STFC-RAL-CR03-RAL-R61-2.01: This is actually remarkably straightforward to do. 79 00:09:54.990 --> 00:10:00.379 STFC-RAL-CR03-RAL-R61-2.01: The densities we're going to use are around 10 to the 18, maybe a little bit lower in cubic centimeters. 80 00:10:00.630 --> 00:10:06.540 STFC-RAL-CR03-RAL-R61-2.01: And if you work out the wave breaking field, it's like subbing. Formally, you get a meter. 81 00:10:07.230 --> 00:10:15.170 STFC-RAL-CR03-RAL-R61-2.01: The plasma periods end about 100 microseconds, and this scale is 30 microns. So these are tiny, tiny accelerating cavities. 82 00:10:16.440 --> 00:10:21.280 STFC-RAL-CR03-RAL-R61-2.01: And… Let me just… Skip through a couple of, 83 00:10:22.350 --> 00:10:26.189 STFC-RAL-CR03-RAL-R61-2.01: key concepts around how we describe the laser field. 84 00:10:26.350 --> 00:10:31.859 STFC-RAL-CR03-RAL-R61-2.01: And… If you imagine… One of the place where that was moving. 85 00:10:32.000 --> 00:10:35.079 STFC-RAL-CR03-RAL-R61-2.01: in the electromagnetic wave. Start with the bone wave. 86 00:10:35.260 --> 00:10:41.540 STFC-RAL-CR03-RAL-R61-2.01: Then you can write down the Reds equation for the motion. You can write the field in terms of the vector potential. A. 87 00:10:42.070 --> 00:10:49.310 STFC-RAL-CR03-RAL-R61-2.01: And if you then normalize that by dividing the momentum by MC. Which is a natural thing to do. Then you keep getting this quantity here. 88 00:10:49.550 --> 00:10:53.490 STFC-RAL-CR03-RAL-R61-2.01: which is a times e over mc. That appears on both sides. 89 00:10:54.200 --> 00:10:57.890 STFC-RAL-CR03-RAL-R61-2.01: And so that's that's a normal effect potential for this lay. 90 00:10:58.130 --> 00:11:15.930 STFC-RAL-CR03-RAL-R61-2.01: and that will typically describe the laser strength in terms of that parameter. And just to be clear, of course, little a is oscillating. Today's oscillating. We're talking about biggest value at the peak of the laser box. That's what people mean when they say a naught, which is the peak value in the laser field. 91 00:11:16.550 --> 00:11:21.189 STFC-RAL-CR03-RAL-R61-2.01: So for engineering purposes, then you can use this formula here. 92 00:11:21.330 --> 00:11:32.470 STFC-RAL-CR03-RAL-R61-2.01: You see that if you have an intensity around 10 to 18, and a wavelength of about one micron, the magnitude is going to be about one, as we'll see in a minute. That's just about the boundary between when this motion 93 00:11:32.570 --> 00:11:39.919 STFC-RAL-CR03-RAL-R61-2.01: of the electrons in the field becomes relativistic. It's very useful way of prioritizing a laser strength. 94 00:11:40.830 --> 00:11:46.740 STFC-RAL-CR03-RAL-R61-2.01: And… Now, what's this force which pushes the urchins around the point of motive force? 95 00:11:46.980 --> 00:12:02.719 STFC-RAL-CR03-RAL-R61-2.01: And so I'm incredibly grateful to Paul Gibbon for writing this in his book. because it gives me an excuse not to spend a lot of time on it, and I don't have the expertise to do that. But 96 00:12:03.370 --> 00:12:05.979 STFC-RAL-CR03-RAL-R61-2.01: I'm just gonna give you a sort of a flavor of it. 97 00:12:06.850 --> 00:12:12.380 STFC-RAL-CR03-RAL-R61-2.01: And what you can do is you can imagine again thinking about the electron moving in the laser field. 98 00:12:12.820 --> 00:12:22.779 STFC-RAL-CR03-RAL-R61-2.01: and solve the motion non-relativistically. So we drop the interaction with the B field. Just think about the wiggling motion of the electron in the electric field of the laser. 99 00:12:23.010 --> 00:12:27.659 STFC-RAL-CR03-RAL-R61-2.01: So the equation of motion is subtrivial. You can integrate that to get velocity. 100 00:12:28.410 --> 00:12:31.960 STFC-RAL-CR03-RAL-R61-2.01: Then you can work out the kinetic energy and take a time average. 101 00:12:32.160 --> 00:12:36.699 STFC-RAL-CR03-RAL-R61-2.01: It's an undergraduate exercise, and you'll see that the energy, of course, goes like 102 00:12:36.980 --> 00:12:39.780 STFC-RAL-CR03-RAL-R61-2.01: the field squared. So it goes like the intensity. 103 00:12:40.660 --> 00:12:42.109 STFC-RAL-CR03-RAL-R61-2.01: That's the equivalent energy. 104 00:12:42.710 --> 00:12:46.240 STFC-RAL-CR03-RAL-R61-2.01: And then you can imagine, this electron 105 00:12:46.380 --> 00:12:55.079 STFC-RAL-CR03-RAL-R61-2.01: interacting with the laser course, and it's going to have a large quiver energy near the peak of the laser, and it's going to be smaller front and back, and smaller sides as well. 106 00:12:55.390 --> 00:12:58.510 STFC-RAL-CR03-RAL-R61-2.01: And you can think of a gradient of that energy as representing a pulse. 107 00:12:58.630 --> 00:13:00.729 STFC-RAL-CR03-RAL-R61-2.01: Months ago. That's the one we did. 108 00:13:01.190 --> 00:13:09.239 STFC-RAL-CR03-RAL-R61-2.01: That's a non-relativistic derivation, if you will, of what the quantum force is. And the key thing is, it's a gradient. 109 00:13:10.930 --> 00:13:23.040 STFC-RAL-CR03-RAL-R61-2.01: If you like, you can think about it in a different way. So imagine the laser coming along horizontally. Metals are wobbling, oscillating in the laser field. and as they oscillate away from the axis. 110 00:13:23.140 --> 00:13:39.450 STFC-RAL-CR03-RAL-R61-2.01: They move into a region of lower field. And so when they're pulled back by the change in the oscillation, they don't come back quite as far. So they sort of do this and then get pushed out, and the modulated force is effectively a time average force accounted for the motion of the electrons. 111 00:13:40.630 --> 00:13:48.630 STFC-RAL-CR03-RAL-R61-2.01: And just as an aside, if you take the velocity we just derived and divide it by C, you can normalize it, of course, and you find that that ratio is A naught. 112 00:13:48.730 --> 00:13:59.589 STFC-RAL-CR03-RAL-R61-2.01: So that's why anyone is Okay, so we'll frequently talk about. Are you not doing this? 113 00:14:00.690 --> 00:14:01.530 STFC-RAL-CR03-RAL-R61-2.01: No. 114 00:14:01.690 --> 00:14:05.320 STFC-RAL-CR03-RAL-R61-2.01: The reason that's important is these things work in different regimes. 115 00:14:05.990 --> 00:14:11.549 STFC-RAL-CR03-RAL-R61-2.01: The the easiest one to think about is the so-called linear regime, where a naught less than one 116 00:14:11.750 --> 00:14:14.429 STFC-RAL-CR03-RAL-R61-2.01: Emotion is not quite relativistic. 117 00:14:14.570 --> 00:14:18.879 STFC-RAL-CR03-RAL-R61-2.01: You find that the density waves you drive sinusoidal. 118 00:14:19.490 --> 00:14:26.069 STFC-RAL-CR03-RAL-R61-2.01: They look a little bit like the picture there, and the period between the peaks and the waves is the plasma wavelength. 119 00:14:26.760 --> 00:14:28.540 STFC-RAL-CR03-RAL-R61-2.01: If you push it a bit harder. 120 00:14:28.690 --> 00:14:30.530 STFC-RAL-CR03-RAL-R61-2.01: Then the waves look a bit like this. 121 00:14:30.810 --> 00:14:34.949 STFC-RAL-CR03-RAL-R61-2.01: You'll see that this fraction becomes much spikier in terms of the density. 122 00:14:35.280 --> 00:14:41.800 STFC-RAL-CR03-RAL-R61-2.01: The electric field you can generate can be bigger than the weight breaking field. 123 00:14:42.190 --> 00:14:47.169 STFC-RAL-CR03-RAL-R61-2.01: and we'll find the electric field adopts a sort of sawtooth profile, as you can see at the moment. 124 00:14:47.590 --> 00:14:50.799 STFC-RAL-CR03-RAL-R61-2.01: One reason for that, and this idea will keep coming up. 125 00:14:51.090 --> 00:14:54.730 STFC-RAL-CR03-RAL-R61-2.01: Is the plasma frequency dependent on the electrical mass? 126 00:14:55.040 --> 00:14:59.859 STFC-RAL-CR03-RAL-R61-2.01: And the electron motion starts to become relativistic, and so this… this is changing during motion. 127 00:15:00.110 --> 00:15:09.619 STFC-RAL-CR03-RAL-R61-2.01: The other reason is that the linear regime relies on linearization of 3rd equations. Of course, and you can't do that anymore. Once once all the entities get to be large. 128 00:15:09.950 --> 00:15:15.649 STFC-RAL-CR03-RAL-R61-2.01: So in one thing, which is my number of dimensions. And 129 00:15:16.090 --> 00:15:18.800 STFC-RAL-CR03-RAL-R61-2.01: This is a solution to the 3rd equations. 130 00:15:18.920 --> 00:15:22.890 STFC-RAL-CR03-RAL-R61-2.01: Here the red is the laser pulse in A naught. So 131 00:15:23.020 --> 00:15:27.710 STFC-RAL-CR03-RAL-R61-2.01: We'll see that when A naught is one, that when A naught is below one. 132 00:15:28.200 --> 00:15:31.089 STFC-RAL-CR03-RAL-R61-2.01: There, if you look at the green line, that's the 133 00:15:31.220 --> 00:15:47.640 STFC-RAL-CR03-RAL-R61-2.01: electrical density. You'll just about convince yourself it's sinusoidal there and then. The derivative part gives you the electric field. That's the yellow. That's also sinusoidal. But as it goes above one it gets very spiky on the electrical density. Big spikes occurring. You'll 134 00:15:47.840 --> 00:15:55.610 STFC-RAL-CR03-RAL-R61-2.01: with your alert, you can see that the spacing changes as well. So they're getting huge density spikes. And you get this sorted elective. 135 00:15:56.270 --> 00:16:01.309 STFC-RAL-CR03-RAL-R61-2.01: So the operation of the system depends a lot on which version. 136 00:16:02.500 --> 00:16:04.519 STFC-RAL-CR03-RAL-R61-2.01: Okay, so, 137 00:16:05.610 --> 00:16:11.100 STFC-RAL-CR03-RAL-R61-2.01: I think you can see how we can. We can generate this plasma weight field structure with big electric fields in. 138 00:16:11.400 --> 00:16:18.140 STFC-RAL-CR03-RAL-R61-2.01: One of the limitations And there are three key limitations. I'll just look at the three D's. 139 00:16:19.760 --> 00:16:27.729 STFC-RAL-CR03-RAL-R61-2.01: One of them is simply the fact that the laser pulse is driving this structure, this weight field, by moving through the plasma, so it's going at the speed of light. 140 00:16:28.140 --> 00:16:33.240 STFC-RAL-CR03-RAL-R61-2.01: the particles we're going to accelerate, which I'm going to maybe talk about electrons. 141 00:16:33.420 --> 00:16:40.220 STFC-RAL-CR03-RAL-R61-2.01: We're sitting here. These become very relative very quickly. So they're going to have gammas of in the 1,000 range. 142 00:16:40.450 --> 00:16:41.350 STFC-RAL-CR03-RAL-R61-2.01: And… 143 00:16:41.760 --> 00:16:58.099 STFC-RAL-CR03-RAL-R61-2.01: So they're going at the speed of light. But of course, the difference is the laser pulse is going at the speed of light in the medium. So it's going at its root velocity, which is a little bit less than C. So after a while, these electrons are moving from acceleration to deceleration, and you need to stop the acceleration for it to stop. 144 00:16:58.460 --> 00:17:02.220 STFC-RAL-CR03-RAL-R61-2.01: So that just defines the scale length with the phasing length. 145 00:17:02.770 --> 00:17:10.200 STFC-RAL-CR03-RAL-R61-2.01: I've given you some expressions there on the expressions for able to be small or large. 146 00:17:10.579 --> 00:17:11.550 STFC-RAL-CR03-RAL-R61-2.01: Umm. 147 00:17:13.060 --> 00:17:17.430 STFC-RAL-CR03-RAL-R61-2.01: And the second… B is the condition. 148 00:17:17.680 --> 00:17:31.360 STFC-RAL-CR03-RAL-R61-2.01: which is that you're going to lose drive energy to the personal wave. It's quite easy to get depressed about this, but that's you have to remind yourself that is what they're trying to do. So you're trying to transfer energy from the laser into the personal wave, and there's a distance over which 149 00:17:31.520 --> 00:17:33.040 STFC-RAL-CR03-RAL-R61-2.01: You depleted the laser. 150 00:17:33.240 --> 00:17:35.849 STFC-RAL-CR03-RAL-R61-2.01: And that's getting those, those, 151 00:17:36.280 --> 00:17:42.449 STFC-RAL-CR03-RAL-R61-2.01: formally there. And what you might notice is they basically depend on the same 152 00:17:42.660 --> 00:17:46.019 STFC-RAL-CR03-RAL-R61-2.01: way on on Omega P. So 153 00:17:46.130 --> 00:17:59.719 STFC-RAL-CR03-RAL-R61-2.01: That's Lambda P is the way that that's that's just one over omega P in disguise. So it goes like one over omega P cubed, and both of you behave the same way. In fact, the distance is not very different depending on the regime. 154 00:18:00.420 --> 00:18:04.040 STFC-RAL-CR03-RAL-R61-2.01: So the graphs are showing the fading length here. 155 00:18:04.310 --> 00:18:13.619 STFC-RAL-CR03-RAL-R61-2.01: I think you can see that. So your 2018 SCC depending on A naught, your depletion length is on the scale of 156 00:18:14.130 --> 00:18:16.170 STFC-RAL-CR03-RAL-R61-2.01: a bit less than a 10 to the meter. 157 00:18:16.320 --> 00:18:19.360 STFC-RAL-CR03-RAL-R61-2.01: So, some sensor features also. 158 00:18:19.550 --> 00:18:34.140 STFC-RAL-CR03-RAL-R61-2.01: and it rapidly gets longer as you drop the density right? You can see how it does that. And then the pump depletion length is is similar. In this case it's longer. 10 to the 18 with with the small A naught. But as A naught cranks up and starts to approach the defacing. 159 00:18:34.370 --> 00:18:38.889 STFC-RAL-CR03-RAL-R61-2.01: So these distances are important to keep in mind when you're designing your accelerator stage. 160 00:18:40.760 --> 00:18:42.170 STFC-RAL-CR03-RAL-R61-2.01: Okay, 161 00:18:42.500 --> 00:18:49.680 STFC-RAL-CR03-RAL-R61-2.01: So now we can estimate the particle gain the energy gain, I should say. So we drop the electron into this structure. We're going to accelerate it. 162 00:18:50.070 --> 00:18:54.639 STFC-RAL-CR03-RAL-R61-2.01: The energy gain is just the work done by the Wakefield on the charge. 163 00:18:54.780 --> 00:18:56.879 STFC-RAL-CR03-RAL-R61-2.01: So yeah, just have to integrate EZ. 164 00:18:57.280 --> 00:19:04.259 STFC-RAL-CR03-RAL-R61-2.01: And so in my hand, maybe way up and say, well, it's about half the maximum times the length of the accelerator. Okay? 165 00:19:05.360 --> 00:19:12.730 STFC-RAL-CR03-RAL-R61-2.01: And so what's the length of the accelerator? Well, it's the it's the bigger of the debating. Okay? So you can pull that together. 166 00:19:13.210 --> 00:19:14.689 STFC-RAL-CR03-RAL-R61-2.01: Get an energy game. 167 00:19:15.130 --> 00:19:19.049 STFC-RAL-CR03-RAL-R61-2.01: and you get expressions like this. So that's the rest of course. 168 00:19:19.290 --> 00:19:27.319 STFC-RAL-CR03-RAL-R61-2.01: Nc. Still, the critical density. It's just a function of the drive wavelength of the laser. So that's a fixed thing for your laser. 169 00:19:28.070 --> 00:19:30.950 STFC-RAL-CR03-RAL-R61-2.01: And then what you're going to see is it goes like one of the things. 170 00:19:31.650 --> 00:19:34.749 STFC-RAL-CR03-RAL-R61-2.01: So… In all the regimes. 171 00:19:35.260 --> 00:19:44.360 STFC-RAL-CR03-RAL-R61-2.01: increase energy means drop density, which might be counterintuitive. What you're doing is you're dropping the electric field within the pulse grid. 172 00:19:45.060 --> 00:19:53.430 STFC-RAL-CR03-RAL-R61-2.01: which is bad. You're increasing the distance, which is maintaining acceleration is good, and that wins. And so you want to go to lower density to get higher. 173 00:19:55.040 --> 00:19:56.199 STFC-RAL-CR03-RAL-R61-2.01: Edge base. 174 00:19:56.810 --> 00:20:02.050 STFC-RAL-CR03-RAL-R61-2.01: So, let me now, with that sort of intro, 175 00:20:02.510 --> 00:20:07.830 STFC-RAL-CR03-RAL-R61-2.01: Give me 4 slides of progress, in in the field. 176 00:20:08.770 --> 00:20:19.409 STFC-RAL-CR03-RAL-R61-2.01: So we can start with this paper here in 1970. It's a very famous paper in the field by Dawson. There were other papers, I think, prior to this mentioning the concept. I think this is the one 177 00:20:20.060 --> 00:20:26.319 STFC-RAL-CR03-RAL-R61-2.01: in terms of what I'm writing on. But I think this is one that really got people interested in this possibility. 178 00:20:26.570 --> 00:20:32.900 STFC-RAL-CR03-RAL-R61-2.01: And so, like any good papers, it's got an abstract that captures all the key details. 179 00:20:33.070 --> 00:20:36.789 STFC-RAL-CR03-RAL-R61-2.01: And in fact, all the details are really in this sentence. 180 00:20:37.600 --> 00:20:39.779 STFC-RAL-CR03-RAL-R61-2.01: So, we have existing data. 181 00:20:40.360 --> 00:20:45.590 STFC-RAL-CR03-RAL-R61-2.01: of power density, 10 to 18, show density, plus also density, 10 to 18 again. 182 00:20:45.800 --> 00:20:51.769 STFC-RAL-CR03-RAL-R61-2.01: Gigavolts per centimeter of observation. That's that's the key idea right there. 183 00:20:51.990 --> 00:20:56.120 STFC-RAL-CR03-RAL-R61-2.01: And it's absolutely… Correct? 184 00:20:56.900 --> 00:21:03.740 STFC-RAL-CR03-RAL-R61-2.01: with some doubt about that word. because it turns out that's actually my heart. 185 00:21:06.150 --> 00:21:08.240 STFC-RAL-CR03-RAL-R61-2.01: But everything else is great. 186 00:21:08.630 --> 00:21:14.709 STFC-RAL-CR03-RAL-R61-2.01: And so the idea was originally, you take a laser pulse from it thought to be short and sort of sitting inside one place period. 187 00:21:15.000 --> 00:21:21.529 STFC-RAL-CR03-RAL-R61-2.01: Rather than plasma waves, as you can see there, but that was difficult with the technology available, because it was difficult to make very short wavelengths. 188 00:21:22.310 --> 00:21:23.970 STFC-RAL-CR03-RAL-R61-2.01: with with also I mentioned. 189 00:21:24.820 --> 00:21:31.490 STFC-RAL-CR03-RAL-R61-2.01: And so the solution that was adopted by many groups was called a beatwave accelerator. 190 00:21:31.680 --> 00:21:37.329 STFC-RAL-CR03-RAL-R61-2.01: in which you take 2 laser pulses at slightly different frequency, omega, one omega, 2. 191 00:21:37.620 --> 00:21:47.700 STFC-RAL-CR03-RAL-R61-2.01: If they differ by the plasma frequency and combine the laser pulses inside the plasma, you're going to get a beating of the envelope, the intensity envelope. 192 00:21:48.230 --> 00:21:53.219 STFC-RAL-CR03-RAL-R61-2.01: As you can see here, And that beat period is actually the past period. 193 00:21:53.560 --> 00:22:04.789 STFC-RAL-CR03-RAL-R61-2.01: So each of these little bumps in this idea, that one there, this one there, that one there, we each drive a little plasma wave because they're spaced by exactly one plasma wavelength. The amplitude grows 194 00:22:04.910 --> 00:22:08.170 STFC-RAL-CR03-RAL-R61-2.01: towards the back of the train. That's the idea. 195 00:22:09.290 --> 00:22:12.839 STFC-RAL-CR03-RAL-R61-2.01: And so lots of work was done. 196 00:22:13.210 --> 00:22:21.399 STFC-RAL-CR03-RAL-R61-2.01: on this in the middle 70s, the middle 80s, I suppose. Middle 80s, I guess. Talked about the UCLA group. 197 00:22:21.820 --> 00:22:25.809 STFC-RAL-CR03-RAL-R61-2.01: You can see some experiments here, but there's too much detail. 198 00:22:26.260 --> 00:22:37.669 STFC-RAL-CR03-RAL-R61-2.01: What's interesting really for us is the electrical energy they could get. You can see it on the 10 Mev scale. But you can also see this is a lot scale. So it's a very, very broad spectrum. 199 00:22:38.600 --> 00:22:53.680 STFC-RAL-CR03-RAL-R61-2.01: One reason for that was just the way they could do the experiments. They threw electrons in from, I think, conventional Rf. So I just threw it into the into the weight field. There was no control as to which phase the weight field going in, and so they were. Some were accelerated and some were decelerated. 200 00:22:54.000 --> 00:22:58.519 STFC-RAL-CR03-RAL-R61-2.01: But you get the idea. You get 10 AB kind of acceleration in just a few millimeters. 201 00:22:59.800 --> 00:23:04.060 STFC-RAL-CR03-RAL-R61-2.01: Now, the reason this didn't progress much further is 202 00:23:04.170 --> 00:23:15.099 STFC-RAL-CR03-RAL-R61-2.01: there's a saturation process that occurs because of this fact I mentioned before, which is that the personal frequency depends upon the gamma of the oscillating electrons in the plasma wave. 203 00:23:15.260 --> 00:23:20.809 STFC-RAL-CR03-RAL-R61-2.01: And so, as the plasma wave grows, Gamma starts to move… increase away from 1. 204 00:23:20.980 --> 00:23:27.990 STFC-RAL-CR03-RAL-R61-2.01: And so you lose this resonance condition because these frequencies are fixed. There's nothing you can do about that. And so you detune all the backwards up. 205 00:23:28.500 --> 00:23:30.859 STFC-RAL-CR03-RAL-R61-2.01: at the back of the train, the back of the 206 00:23:30.960 --> 00:23:37.489 STFC-RAL-CR03-RAL-R61-2.01: drive once the amplitude gets too big, so you kind of clamp the amplitude. That's what the rose of this loop. 207 00:23:37.750 --> 00:23:38.750 STFC-RAL-CR03-RAL-R61-2.01: Limit. 208 00:23:38.880 --> 00:23:46.330 STFC-RAL-CR03-RAL-R61-2.01: And that sort of put a stop to my research on on that idea. 209 00:23:47.150 --> 00:23:50.769 STFC-RAL-CR03-RAL-R61-2.01: And… So, the next thing which happened was… 210 00:23:50.930 --> 00:23:54.079 STFC-RAL-CR03-RAL-R61-2.01: to these coaches, both Richard and John Maru. 211 00:23:54.520 --> 00:23:59.029 STFC-RAL-CR03-RAL-R61-2.01: Who, in roughly 9, 85 proposed 212 00:23:59.170 --> 00:24:03.450 STFC-RAL-CR03-RAL-R61-2.01: A solution to a problem The technological problem, which was 213 00:24:03.720 --> 00:24:07.950 STFC-RAL-CR03-RAL-R61-2.01: It's actually relatively easy to make at this point short pulses. 214 00:24:08.060 --> 00:24:10.080 STFC-RAL-CR03-RAL-R61-2.01: on the 50 millisecond scale. 215 00:24:10.360 --> 00:24:19.779 STFC-RAL-CR03-RAL-R61-2.01: Amplifying was difficult, because as you start to add energy to the poles, you increase its power, increase its peak intensity, and then it starts to drill holes in all the optics. 216 00:24:20.190 --> 00:24:22.430 STFC-RAL-CR03-RAL-R61-2.01: And so the way around that is to make the beam bigger. 217 00:24:22.710 --> 00:24:27.070 STFC-RAL-CR03-RAL-R61-2.01: Not intensively, but then it gets expensive, and you can't make your office bigger. 218 00:24:27.480 --> 00:24:32.439 STFC-RAL-CR03-RAL-R61-2.01: So the the neat idea they came up with is called pulse amplification. 219 00:24:32.840 --> 00:24:34.410 STFC-RAL-CR03-RAL-R61-2.01: And it used to the fact that. 220 00:24:34.580 --> 00:24:38.799 STFC-RAL-CR03-RAL-R61-2.01: A very short driving data pulse must contain it. 221 00:24:38.910 --> 00:24:41.170 STFC-RAL-CR03-RAL-R61-2.01: Of, well, bandwidth and frequencies. 222 00:24:41.350 --> 00:24:46.979 STFC-RAL-CR03-RAL-R61-2.01: So you can take a short pulse from an oscillator, pass it through a system that's dispersive. 223 00:24:47.440 --> 00:24:53.210 STFC-RAL-CR03-RAL-R61-2.01: So that just means hopefully different frequencies at different times coming through the system, the fraction ratings for that. 224 00:24:53.730 --> 00:24:58.059 STFC-RAL-CR03-RAL-R61-2.01: So you in this case you have the the red coming up for the blue. 225 00:24:58.740 --> 00:25:03.989 STFC-RAL-CR03-RAL-R61-2.01: You can stretch it by a factor on the scale of 10,000, or even 100,000, in time. 226 00:25:04.310 --> 00:25:09.309 STFC-RAL-CR03-RAL-R61-2.01: I suppose it's then shut because it makes it a bit like a bird song frequency swept. 227 00:25:09.890 --> 00:25:15.989 STFC-RAL-CR03-RAL-R61-2.01: You've got that sort of big power by a factor of 10,000 or 100,000, you can then add the engine back, the amplifiers. 228 00:25:16.350 --> 00:25:22.210 STFC-RAL-CR03-RAL-R61-2.01: And then you reverse the stretch in in the thing. Imagine if you pull the compressor. 229 00:25:22.670 --> 00:25:28.269 STFC-RAL-CR03-RAL-R61-2.01: which puts the faults back together again. And now you have a high energy and high potential. 230 00:25:29.200 --> 00:25:38.360 STFC-RAL-CR03-RAL-R61-2.01: It's really extraordinary. This stuff works because you think about it. You have optical policies going through many tens of meters of light space, many centimeters. 231 00:25:38.520 --> 00:25:39.550 STFC-RAL-CR03-RAL-R61-2.01: Crystal. 232 00:25:39.740 --> 00:25:45.359 STFC-RAL-CR03-RAL-R61-2.01: and the the phase gain by each frequency has to be perfectly matched. But it works. 233 00:25:45.770 --> 00:25:53.219 STFC-RAL-CR03-RAL-R61-2.01: So you can see in the picture at the bottom. This is an example of a large tri-sapphire system. 234 00:25:53.920 --> 00:25:57.859 STFC-RAL-CR03-RAL-R61-2.01: It produces 40 joules in 33 volts per second. 235 00:25:58.190 --> 00:26:02.149 STFC-RAL-CR03-RAL-R61-2.01: So in 30 femtoseconds, light travels 10 microns. 236 00:26:02.790 --> 00:26:06.959 STFC-RAL-CR03-RAL-R61-2.01: So you have also just 10 microns thick, which may be a bit of 237 00:26:07.270 --> 00:26:09.890 STFC-RAL-CR03-RAL-R61-2.01: 100 millimeters or so in diameter. 238 00:26:10.420 --> 00:26:16.259 STFC-RAL-CR03-RAL-R61-2.01: containing 40 joules of energy flying around. And this can be done once per second. 239 00:26:16.540 --> 00:26:19.580 STFC-RAL-CR03-RAL-R61-2.01: So that's the drive energy, the drive system. 240 00:26:20.980 --> 00:26:27.680 STFC-RAL-CR03-RAL-R61-2.01: So with that, a new regime was opened. This was actually discovered, I think, theoretically first, but then quickly demonstrated. 241 00:26:28.090 --> 00:26:39.029 STFC-RAL-CR03-RAL-R61-2.01: In the labs, that's called the bubble rating, where you really focus to a small spot, and you drive a very strong rate field, so A0 is well above 2. 242 00:26:39.410 --> 00:26:46.359 STFC-RAL-CR03-RAL-R61-2.01: But in this regime, you the contrary force is so strong that all of the electrons 243 00:26:46.840 --> 00:26:51.600 STFC-RAL-CR03-RAL-R61-2.01: in the region of the drive of spell. So you can see that in the simulation at the top. 244 00:26:51.770 --> 00:26:55.249 STFC-RAL-CR03-RAL-R61-2.01: So this region here, there are 245 00:26:55.370 --> 00:27:00.899 STFC-RAL-CR03-RAL-R61-2.01: So if you know you form what's called a bubble sitting right behind the driver. So it's devoid of electrons. 246 00:27:01.140 --> 00:27:07.880 STFC-RAL-CR03-RAL-R61-2.01: That's a nice structure, because it turns out the electric fields inside that nearly spherical region are 247 00:27:08.110 --> 00:27:11.650 STFC-RAL-CR03-RAL-R61-2.01: Ideal for focusing, because the range of field 248 00:27:11.820 --> 00:27:14.770 STFC-RAL-CR03-RAL-R61-2.01: Very linearly distance away from the axis. 249 00:27:15.310 --> 00:27:21.200 STFC-RAL-CR03-RAL-R61-2.01: You also get… self injections. You can see that occurring right now. So these electrons here 250 00:27:21.510 --> 00:27:28.100 STFC-RAL-CR03-RAL-R61-2.01: have float float around the inside of the problem, albeit and they're not being accelerated. 251 00:27:28.440 --> 00:27:40.279 STFC-RAL-CR03-RAL-R61-2.01: And that makes it easy experimentally. You just fire the data into the target. More volatility, more electrons come out. And so people got very excited about this because it was very easy to make electron beams. 252 00:27:40.480 --> 00:27:41.420 STFC-RAL-CR03-RAL-R61-2.01: this way. 253 00:27:41.840 --> 00:27:45.020 STFC-RAL-CR03-RAL-R61-2.01: You can see some interesting features as well in the simulation, because 254 00:27:45.190 --> 00:27:54.510 STFC-RAL-CR03-RAL-R61-2.01: The electrons which were injected. These these 2 things here are oscillating in the transverse field. That's the beta formation. And that would be brought to X-ray emission. 255 00:27:54.690 --> 00:27:56.810 STFC-RAL-CR03-RAL-R61-2.01: And they're also moving ahead. 256 00:27:57.420 --> 00:28:01.929 STFC-RAL-CR03-RAL-R61-2.01: relative to the laser, because they're going faster than the laser. That's the deep phasing process. 257 00:28:04.050 --> 00:28:13.559 STFC-RAL-CR03-RAL-R61-2.01: So very quickly. People started making beans like this. So the top one was done here. 258 00:28:13.700 --> 00:28:28.699 STFC-RAL-CR03-RAL-R61-2.01: You can see that it's now a spectrum that is not broadband, still brought by proper accelerator standards, but it's got a peak around 1830 V. This result is from Aloha in Paris, and this result from Berkeley. 259 00:28:29.500 --> 00:28:33.540 STFC-RAL-CR03-RAL-R61-2.01: were published in the same edition of Nature, and this was a really important moment. 260 00:28:33.820 --> 00:28:36.060 STFC-RAL-CR03-RAL-R61-2.01: with the field back in 2,004. 261 00:28:36.380 --> 00:28:40.919 STFC-RAL-CR03-RAL-R61-2.01: because people started to take it a bit more seriously. 262 00:28:43.010 --> 00:28:47.480 STFC-RAL-CR03-RAL-R61-2.01: I think that's the end of my yeah survey progress. 263 00:28:47.810 --> 00:28:50.440 STFC-RAL-CR03-RAL-R61-2.01: But now I wanted to just talk about. 264 00:28:50.940 --> 00:28:57.769 STFC-RAL-CR03-RAL-R61-2.01: What can you do to increase the energy more? Because, okay, some of the EV is nice, but maybe we'd like a DEDB. 265 00:28:58.050 --> 00:29:01.660 STFC-RAL-CR03-RAL-R61-2.01: So how do you do that? And you're still awake. 266 00:29:02.090 --> 00:29:04.669 STFC-RAL-CR03-RAL-R61-2.01: You'll realize I missed one of the P's out. 267 00:29:04.940 --> 00:29:11.190 STFC-RAL-CR03-RAL-R61-2.01: There are 3 processes that limit acceleration. And this third one is defecting. 268 00:29:12.380 --> 00:29:17.609 STFC-RAL-CR03-RAL-R61-2.01: So if you focus the laser down to a small slot size, which you need to do, you need a high intensity. 269 00:29:18.010 --> 00:29:19.949 STFC-RAL-CR03-RAL-R61-2.01: And then it'll actually diffract. 270 00:29:20.130 --> 00:29:24.149 STFC-RAL-CR03-RAL-R61-2.01: And the scale is very, very interesting by this expression here. 271 00:29:24.330 --> 00:29:30.169 STFC-RAL-CR03-RAL-R61-2.01: where W naught is the transverse scale of the focus. So it's the size of the focus. 272 00:29:31.270 --> 00:29:32.800 STFC-RAL-CR03-RAL-R61-2.01: deployed it somewhere. 273 00:29:32.930 --> 00:29:37.279 STFC-RAL-CR03-RAL-R61-2.01: And… So if you take an example, maybe 10 microphone focus spots. 274 00:29:37.600 --> 00:29:42.869 STFC-RAL-CR03-RAL-R61-2.01: for the micro. So then, this radio range is is so that's the one we look at. 275 00:29:43.080 --> 00:29:46.509 STFC-RAL-CR03-RAL-R61-2.01: So these experiments are done with millimeter scale interactions. 276 00:29:47.880 --> 00:29:48.770 STFC-RAL-CR03-RAL-R61-2.01: And… 277 00:29:49.660 --> 00:29:57.179 STFC-RAL-CR03-RAL-R61-2.01: The energy gain that we've already seen is the product of the field inside the wave field times the length over which you can accelerate. 278 00:29:57.530 --> 00:30:00.979 STFC-RAL-CR03-RAL-R61-2.01: If you can accelerate, if you can beat this limit somehow. 279 00:30:02.300 --> 00:30:12.249 STFC-RAL-CR03-RAL-R61-2.01: then you're limited by either dephasing or completion. They're both varying in the same way of density, and as we've already seen. that means energy gain goes to one over density. 280 00:30:12.560 --> 00:30:15.390 STFC-RAL-CR03-RAL-R61-2.01: So if I want to go from 100 MV to a GEV, 281 00:30:15.630 --> 00:30:18.959 STFC-RAL-CR03-RAL-R61-2.01: We need to drop the density by 10. The cost of that 282 00:30:19.280 --> 00:30:23.100 STFC-RAL-CR03-RAL-R61-2.01: It's a distance over which we have to maintain. The acceleration goes up by 30. 283 00:30:23.330 --> 00:30:29.379 STFC-RAL-CR03-RAL-R61-2.01: So you're looking not at millimeter scale, but it's many centimeters scale. 284 00:30:29.540 --> 00:30:31.300 STFC-RAL-CR03-RAL-R61-2.01: So that's… that's the challenge. 285 00:30:31.830 --> 00:30:32.740 STFC-RAL-CR03-RAL-R61-2.01: And. 286 00:30:32.930 --> 00:30:38.789 STFC-RAL-CR03-RAL-R61-2.01: And the solution, generically, is to use what's called a gradient refractive index, where we've got it. 287 00:30:39.780 --> 00:30:43.669 STFC-RAL-CR03-RAL-R61-2.01: So for those who are not opticians. 288 00:30:44.310 --> 00:30:48.570 STFC-RAL-CR03-RAL-R61-2.01: The basic idea is you want a structure in which your refractive index, I'm going to call it ether. 289 00:30:48.750 --> 00:30:53.619 STFC-RAL-CR03-RAL-R61-2.01: varies with transverse position. They want to be peaked in the middle and small at the edge. 290 00:30:54.470 --> 00:31:01.699 STFC-RAL-CR03-RAL-R61-2.01: You have such a system that each wavefront, as it propagates, will propagate a bit faster on the edge than in the middle, so it starts to curve in. 291 00:31:02.100 --> 00:31:03.300 STFC-RAL-CR03-RAL-R61-2.01: So it's focusing. 292 00:31:03.700 --> 00:31:13.390 STFC-RAL-CR03-RAL-R61-2.01: or you can think of taking that medium slightly up, and each slice looks like a little lens. And so that will counteract the diffractory process. And so this, that's basically what you need to make. 293 00:31:14.190 --> 00:31:15.080 STFC-RAL-CR03-RAL-R61-2.01: Bill? 294 00:31:15.200 --> 00:31:20.700 STFC-RAL-CR03-RAL-R61-2.01: I think this is almost well, pretty much a unique case in which plasma is helpful. 295 00:31:20.920 --> 00:31:30.169 STFC-RAL-CR03-RAL-R61-2.01: Because this happens naturally. If if you take the transverse profile of the laser pulse, it's lasers going left to right. 296 00:31:30.780 --> 00:31:38.480 STFC-RAL-CR03-RAL-R61-2.01: It's going to be peaked in the middle in terms of intensity, it's smaller at the edge. The equivalent motion was discussed is bigger on axis than in the wings. 297 00:31:39.030 --> 00:31:45.200 STFC-RAL-CR03-RAL-R61-2.01: So if I look at my formula for the refractory next plasma, which you might remember from your undergraduate days. 298 00:31:45.480 --> 00:31:54.260 STFC-RAL-CR03-RAL-R61-2.01: There's like a V. I expand that square root. There's a gamma on the bottom, as we mentioned a number of times, and that's just in the right place. 299 00:31:54.470 --> 00:31:58.449 STFC-RAL-CR03-RAL-R61-2.01: for that variation to give refractory method peaks on axis. 300 00:31:58.780 --> 00:32:02.330 STFC-RAL-CR03-RAL-R61-2.01: Tesla Broadspeed is self-purposing. There's a critical part for it. 301 00:32:02.610 --> 00:32:10.219 STFC-RAL-CR03-RAL-R61-2.01: You work that out, and as you can see in this graph here, the sort of numbers you get, the sort of densities we're running at. 302 00:32:10.370 --> 00:32:12.120 STFC-RAL-CR03-RAL-R61-2.01: There's a few tens of terabytes. 303 00:32:12.390 --> 00:32:20.669 STFC-RAL-CR03-RAL-R61-2.01: This is exactly where people are operating. So this is definitely going to happen in the experiment you do. So this already, in fact, extends the interaction. 304 00:32:21.820 --> 00:32:27.920 STFC-RAL-CR03-RAL-R61-2.01: Now, one thing to be aware of, of course, is the slight danger of it running away because you get more and more focus in, and maybe you can't control it. 305 00:32:28.240 --> 00:32:30.079 STFC-RAL-CR03-RAL-R61-2.01: as much as you'd like to. 306 00:32:30.430 --> 00:32:37.469 STFC-RAL-CR03-RAL-R61-2.01: So something my group has been working on is the other way of doing it, which is to shake the plasma. 307 00:32:38.260 --> 00:32:50.579 STFC-RAL-CR03-RAL-R61-2.01: So to try and control refractive index in the same sort of way. But now you need an electrical density which is lower in the middle than at the edge. Right? Because then, when you write your refractive index, it goes like this. That's the right shape. 308 00:32:51.280 --> 00:32:55.280 STFC-RAL-CR03-RAL-R61-2.01: So you need, somehow, to make this… That's the channel. 309 00:32:55.810 --> 00:32:58.750 STFC-RAL-CR03-RAL-R61-2.01: If it's quadratic. 310 00:32:59.580 --> 00:33:04.920 STFC-RAL-CR03-RAL-R61-2.01: So if the variation of electrical density of base, this sort of There you go. 311 00:33:05.540 --> 00:33:11.289 STFC-RAL-CR03-RAL-R61-2.01: then you can match a Gaussian beam. So that's just a laser beam of the Gaussian transverse profile. 312 00:33:11.490 --> 00:33:23.529 STFC-RAL-CR03-RAL-R61-2.01: So here Wm. Is a funny way of writing quadratic dependence. But the reason I've done it is Wm is just the match spot size of your laser pulse. 313 00:33:23.830 --> 00:33:27.230 STFC-RAL-CR03-RAL-R61-2.01: So the question is, how do you do that? Because I'm going to allow myself one slide. 314 00:33:27.690 --> 00:33:32.470 STFC-RAL-CR03-RAL-R61-2.01: deep history. So Jackie's around 2,000 or so. 315 00:33:32.630 --> 00:33:33.500 STFC-RAL-CR03-RAL-R61-2.01: And… 316 00:33:33.720 --> 00:33:44.760 STFC-RAL-CR03-RAL-R61-2.01: exactly for a first graduate student. We developed a thing, for the capillary discharge waveguide. It's very, very simple. You take, a capillary of, maybe. 317 00:33:45.210 --> 00:33:47.160 STFC-RAL-CR03-RAL-R61-2.01: 300 micron diameter. 318 00:33:47.290 --> 00:33:51.120 STFC-RAL-CR03-RAL-R61-2.01: dilute hydrogen gas, run a discharge in there. That's your pulse discharge. 319 00:33:51.360 --> 00:33:53.759 STFC-RAL-CR03-RAL-R61-2.01: which I notice the hydrogen. It gets it hot. 320 00:33:54.270 --> 00:34:00.450 STFC-RAL-CR03-RAL-R61-2.01: And then heat conduction to the wall means we end up with a hot plasma in the middle and a cold plasma at the edge. 321 00:34:00.670 --> 00:34:03.610 STFC-RAL-CR03-RAL-R61-2.01: The pressure across here is essentially constant. 322 00:34:03.950 --> 00:34:05.020 STFC-RAL-CR03-RAL-R61-2.01: So… 323 00:34:05.170 --> 00:34:11.939 STFC-RAL-CR03-RAL-R61-2.01: And so, therefore, you have a plasma that's hot and low density in the middle, cold and high density at the edge. And that's the right shape. 324 00:34:12.739 --> 00:34:17.540 STFC-RAL-CR03-RAL-R61-2.01: to make a channel. You can see the movie. That's that's actually data. 325 00:34:17.820 --> 00:34:28.310 STFC-RAL-CR03-RAL-R61-2.01: taken during the day during the discharge pulse for a square or something. You can see the form of the channel in the middle of the discharge. 326 00:34:28.500 --> 00:34:32.449 STFC-RAL-CR03-RAL-R61-2.01: That you can use to guide these very intense laser pulses. 327 00:34:32.870 --> 00:34:35.130 STFC-RAL-CR03-RAL-R61-2.01: Essentially, we scaled them, so we… 328 00:34:35.260 --> 00:34:41.109 STFC-RAL-CR03-RAL-R61-2.01: Took this to Berkeley, to work with Will Beams and his group, and we managed to generate 329 00:34:41.310 --> 00:34:51.440 STFC-RAL-CR03-RAL-R61-2.01: beamed at one Gv. You see here for the 1st time. So this is the 1st time that this sort of approach had led to kind of singleton scale energies. 330 00:34:52.610 --> 00:34:55.149 STFC-RAL-CR03-RAL-R61-2.01: Since then, we've moved on, 331 00:34:55.650 --> 00:35:02.999 STFC-RAL-CR03-RAL-R61-2.01: by going back in time and looking at an all optical way of doing the same thing. 332 00:35:03.320 --> 00:35:09.060 STFC-RAL-CR03-RAL-R61-2.01: And the reason for that is obvious. You've got a lot of structure in the photo from above. 333 00:35:09.560 --> 00:35:12.850 STFC-RAL-CR03-RAL-R61-2.01: You're going to put a dual laser light through here. 334 00:35:13.040 --> 00:35:23.979 STFC-RAL-CR03-RAL-R61-2.01: maybe eventually the Kilohertz repetition rate. And that's a fantastic, amazing, amazing machining tool which just fill the whole day nearby. So these don't necessarily last very long. 335 00:35:24.820 --> 00:35:26.140 STFC-RAL-CR03-RAL-R61-2.01: So we wanted to go. 336 00:35:26.620 --> 00:35:29.120 STFC-RAL-CR03-RAL-R61-2.01: about the more logical way of doing it. 337 00:35:29.300 --> 00:35:40.009 STFC-RAL-CR03-RAL-R61-2.01: Which is based on… something that Hal Bill spoke about in Maryland back in basically the mid-1990s. 338 00:35:40.290 --> 00:35:45.000 STFC-RAL-CR03-RAL-R61-2.01: And the idea is a very nice one. You take what's called an axicon, so an axicon's a cone. 339 00:35:45.240 --> 00:35:46.670 STFC-RAL-CR03-RAL-R61-2.01: There's a conical lens. 340 00:35:46.960 --> 00:35:52.129 STFC-RAL-CR03-RAL-R61-2.01: and put a laser pulse through it, and that makes what's called a vessel beam. So it spikes along the 341 00:35:52.460 --> 00:35:56.549 STFC-RAL-CR03-RAL-R61-2.01: access. These these wobbles mean that there are rings surrounding that. 342 00:35:57.130 --> 00:36:04.559 STFC-RAL-CR03-RAL-R61-2.01: And this… high intensity spike propagates over a long distance. Distance is just given by the geometric 343 00:36:04.780 --> 00:36:08.450 STFC-RAL-CR03-RAL-R61-2.01: The intersection between this ray, which is refracted, is like a prism. 344 00:36:08.570 --> 00:36:17.059 STFC-RAL-CR03-RAL-R61-2.01: I can track it down to this end, raise it here in the center, I can track it down to there, and that gives you the distance over which you can maintain that high intensity. 345 00:36:17.320 --> 00:36:21.170 STFC-RAL-CR03-RAL-R61-2.01: And in practice you can make these things about a meeting. It's very long. 346 00:36:21.870 --> 00:36:31.120 STFC-RAL-CR03-RAL-R61-2.01: So in the original idea, a laser pulse is used to make a column of plasma. So you use somewhat energetic laser pulse, maybe 100 picoseconds long. 347 00:36:31.500 --> 00:36:38.090 STFC-RAL-CR03-RAL-R61-2.01: What it's doing is it ionizes a few electrons, and then it oscillates electrons that quiver again in the laser field. 348 00:36:38.800 --> 00:36:55.229 STFC-RAL-CR03-RAL-R61-2.01: They undergo collisions with the neutral gas and the ions you have around there, and ionizes them. It's a sort of laser-driven collision, visual ionization process, and if you keep that going for long enough, you can fully ionize the plasma, and you get it hot. 349 00:36:56.200 --> 00:37:09.899 STFC-RAL-CR03-RAL-R61-2.01: So now you have a column of plasma that maybe it's 10 microns across, and it's super hot, and it will expand. So if you look along along this, you see the initial column like this, and then it expands, drives a shock wave out into the surrounding gas. 350 00:37:10.060 --> 00:37:15.330 STFC-RAL-CR03-RAL-R61-2.01: and inside the shockwave you have a plastic channel structure. 351 00:37:16.640 --> 00:37:20.430 STFC-RAL-CR03-RAL-R61-2.01: So what's really nice about this approach is these things float in space. 352 00:37:20.540 --> 00:37:23.749 STFC-RAL-CR03-RAL-R61-2.01: There's not much around that can be damaged by a drive laser. 353 00:37:23.930 --> 00:37:28.009 STFC-RAL-CR03-RAL-R61-2.01: And you can just make a fresh channel at the time you want to. 354 00:37:28.140 --> 00:37:29.690 STFC-RAL-CR03-RAL-R61-2.01: So office. 355 00:37:30.510 --> 00:37:31.979 STFC-RAL-CR03-RAL-R61-2.01: Whoops, I'll be… 356 00:37:32.350 --> 00:37:40.259 STFC-RAL-CR03-RAL-R61-2.01: Not ideal for this situation is you need a high density, so you need to be above 10 to the 18th CC to get the heating, because it's collision with heating. 357 00:37:40.970 --> 00:37:46.919 STFC-RAL-CR03-RAL-R61-2.01: So we we took another look at this and proposed a different way, which is. 358 00:37:47.480 --> 00:37:48.929 STFC-RAL-CR03-RAL-R61-2.01: Do an organization. 359 00:37:49.190 --> 00:37:53.579 STFC-RAL-CR03-RAL-R61-2.01: For those who don't know, optical field ionization occurs at much higher rate intensities. 360 00:37:53.700 --> 00:37:59.009 STFC-RAL-CR03-RAL-R61-2.01: where the laser field is on the scale of the field that holds the electrons into the atom of the arm. 361 00:37:59.480 --> 00:38:04.940 STFC-RAL-CR03-RAL-R61-2.01: So in this sort of cartoon, you have a kilo field holding a metal in, that's its ground state. 362 00:38:05.150 --> 00:38:07.289 STFC-RAL-CR03-RAL-R61-2.01: The laser field, which is a potential 363 00:38:07.490 --> 00:38:11.329 STFC-RAL-CR03-RAL-R61-2.01: energy versus distance diagram. So the laser field is in a straight line. 364 00:38:11.690 --> 00:38:20.499 STFC-RAL-CR03-RAL-R61-2.01: and if it's strong enough, it distorts the potential electron is sitting in and forms a barrier through which the electrons can ionize. 365 00:38:20.620 --> 00:38:23.150 STFC-RAL-CR03-RAL-R61-2.01: But crank up the laser intensity a little bit more. 366 00:38:23.290 --> 00:38:26.519 STFC-RAL-CR03-RAL-R61-2.01: I can completely remove that barrier, and they just fall out. 367 00:38:26.790 --> 00:38:36.929 STFC-RAL-CR03-RAL-R61-2.01: and then they're going to be oscillating in the laser fields. Really, caustic laser fields oscillating the ionization, nothing, ionization, nothing. Ionization. You get constant electrons coming out. 368 00:38:37.720 --> 00:38:41.770 STFC-RAL-CR03-RAL-R61-2.01: You then move in the laser field, and they can pick up energy from the laser field. 369 00:38:42.390 --> 00:38:56.740 STFC-RAL-CR03-RAL-R61-2.01: and we look at the detail, which is really straightforward. It's just classical mechanics. You find that if the field is linearly polarized, the electrons are left with very little energy at the end of the laser pulse. They're circularly polarized. They have high energies. 370 00:38:56.840 --> 00:39:01.979 STFC-RAL-CR03-RAL-R61-2.01: With an interesting distribution which is to do with the ionization energy of each electron. 371 00:39:02.380 --> 00:39:05.370 STFC-RAL-CR03-RAL-R61-2.01: So this, this is a way of getting very hot electrons. 372 00:39:05.670 --> 00:39:10.360 STFC-RAL-CR03-RAL-R61-2.01: But the point is, this occurs on a one-atom basis, so it works at any density. 373 00:39:10.620 --> 00:39:12.859 STFC-RAL-CR03-RAL-R61-2.01: Okay, so you can drop the desk right down. 374 00:39:13.120 --> 00:39:17.450 STFC-RAL-CR03-RAL-R61-2.01: and still get other electrons, and then use the same sort of approach in the channels. 375 00:39:18.030 --> 00:39:19.719 STFC-RAL-CR03-RAL-R61-2.01: but it must have identities. 376 00:39:20.090 --> 00:39:22.950 STFC-RAL-CR03-RAL-R61-2.01: And… Oh, good. 377 00:39:23.330 --> 00:39:31.690 STFC-RAL-CR03-RAL-R61-2.01: So you can see a photo of one here. This is Berlin, Munich, with the Harsh. You can see this this channel floating inside the middle of the vacuum. 378 00:39:32.980 --> 00:39:40.139 STFC-RAL-CR03-RAL-R61-2.01: And so we tested this idea in Astra laser, wherever that is around here somewhere. 379 00:39:40.310 --> 00:39:48.000 STFC-RAL-CR03-RAL-R61-2.01: And we saw something interesting occurring, so these are… thoughts of the… 380 00:39:48.490 --> 00:39:51.470 STFC-RAL-CR03-RAL-R61-2.01: There's a profile coming into the… to the… 381 00:39:52.100 --> 00:40:03.249 STFC-RAL-CR03-RAL-R61-2.01: And also this is the input. This is the transverse dimensions here that's supposed to stop. And it's not too bad. This is what it looks like at the end of the channel. We just made a 16 channel, so it's been beautifully guided. 382 00:40:03.400 --> 00:40:08.669 STFC-RAL-CR03-RAL-R61-2.01: But we noticed that the power coming through increased as we cranked up the laser energy going in. 383 00:40:09.150 --> 00:40:15.369 STFC-RAL-CR03-RAL-R61-2.01: But also, more interestingly, we noticed that if we put a probe across this structure. 384 00:40:15.720 --> 00:40:31.660 STFC-RAL-CR03-RAL-R61-2.01: You can see this here. So this this is the yellow is making the channel, and the red is is being guided. We'll throw across here. If you just have the channel for me being, you can see, I think you can see this kind of column. That's the channel that we're making. I mean this. 385 00:40:32.210 --> 00:40:37.709 STFC-RAL-CR03-RAL-R61-2.01: We're doing this by interferometry with a phase shift on the 100 milligram level. So very slightly easy measurement. 386 00:40:38.700 --> 00:40:46.619 STFC-RAL-CR03-RAL-R61-2.01: But you then you did the same thing. You put a policy in which we're going to guide, and we've timed it up just nicely. So here's the laser pulse coming in. 387 00:40:46.760 --> 00:40:54.050 STFC-RAL-CR03-RAL-R61-2.01: You can see that there's a lot more phase shifts. There's a lot more electrons in that region there. This is before the later ports arrives at South Pacific. 388 00:40:54.340 --> 00:41:00.119 STFC-RAL-CR03-RAL-R61-2.01: And so it's clear that it's ionizing something around the channel or in the channel. 389 00:41:01.100 --> 00:41:12.760 STFC-RAL-CR03-RAL-R61-2.01: And the answer turned out to be, this is work done by fixing one of my students. If you work out the natural density you have here initially, you have this blank curve. So this is this is a plastic channel. It's very. 390 00:41:13.310 --> 00:41:23.540 STFC-RAL-CR03-RAL-R61-2.01: just there. But after the later pulse has been free, you have this enormously deep. That's the channel near the axis, right? And what's happening? 391 00:41:24.000 --> 00:41:30.680 STFC-RAL-CR03-RAL-R61-2.01: is you do indeed drive a shock wave with this approach, but it's not as strong as the original. 392 00:41:31.000 --> 00:41:35.859 STFC-RAL-CR03-RAL-R61-2.01: But what it is doing is it's pushing out a collar of neutrals. 393 00:41:36.350 --> 00:41:41.940 STFC-RAL-CR03-RAL-R61-2.01: with their snow cloud out, if you will, so you can see they pile up as this shock drives out. 394 00:41:42.350 --> 00:41:44.759 STFC-RAL-CR03-RAL-R61-2.01: And then when you try guiding your laser pulse. 395 00:41:45.260 --> 00:41:50.190 STFC-RAL-CR03-RAL-R61-2.01: The transverse wings of the laser force have enough field to ionize. 396 00:41:50.410 --> 00:41:52.110 STFC-RAL-CR03-RAL-R61-2.01: particle species. 397 00:41:52.420 --> 00:41:57.340 STFC-RAL-CR03-RAL-R61-2.01: Here's a simulation by Alex. So this is the initial lateral density distribution. 398 00:41:57.370 --> 00:42:13.940 STFC-RAL-CR03-RAL-R61-2.01: At the front, the initial shock is the laser pulse, and then you can see all this extra ionization occurring in the wings, where the neutral hydrogen is being ionized by the transistor profile. So it sort of builds itself in its own channel from the initial channel made by this optical field ionization technique. 399 00:42:14.540 --> 00:42:17.269 STFC-RAL-CR03-RAL-R61-2.01: So these teams have now got their own literature. 400 00:42:17.760 --> 00:42:21.850 STFC-RAL-CR03-RAL-R61-2.01: As I'll show you in a minute, here's some guiding results for the Gemini laser. 401 00:42:22.080 --> 00:42:41.829 STFC-RAL-CR03-RAL-R61-2.01: Here's again the input beam. It's not a perfect beam. Sorry about that. This is what you see 50 millimeters away from the focus. If you're not doing anything, you focus the beam diffracts. You just see this mess. If you put the channel in, you have beam like it, so it's being rather nicely guided. 402 00:42:41.970 --> 00:42:44.879 STFC-RAL-CR03-RAL-R61-2.01: we need not that in a hundred. So 403 00:42:45.090 --> 00:42:53.369 STFC-RAL-CR03-RAL-R61-2.01: This is really becoming a sort of channel of choice. If you will, there's a lot of literature around them. 404 00:42:53.410 --> 00:43:07.959 STFC-RAL-CR03-RAL-R61-2.01: This is more results from from Berkeley, where they now use this approach to get beams at the sort of nearly 8 Gv. Level, etc, etc. So it's even been taken seriously by people who do rear accelerators. 405 00:43:08.520 --> 00:43:12.729 STFC-RAL-CR03-RAL-R61-2.01: So in Daisy, they're upgrading their signature, etc. 406 00:43:12.860 --> 00:43:19.389 STFC-RAL-CR03-RAL-R61-2.01: to 4, and one of the options for the injection making the infantis inject into the synchrotron. 407 00:43:19.520 --> 00:43:21.530 STFC-RAL-CR03-RAL-R61-2.01: There's a laser different accelerator. 408 00:43:21.790 --> 00:43:28.220 STFC-RAL-CR03-RAL-R61-2.01: 6 Gb. And right at the heart of that is one of these channels, because if you do the wrong event, you need to get to the multi-gb. 409 00:43:28.680 --> 00:43:29.610 STFC-RAL-CR03-RAL-R61-2.01: Right. 410 00:43:30.620 --> 00:43:32.739 STFC-RAL-CR03-RAL-R61-2.01: Okay, so, 411 00:43:34.270 --> 00:43:39.219 STFC-RAL-CR03-RAL-R61-2.01: In the last… not half, the last part, I want to talk a little bit more about 412 00:43:39.490 --> 00:43:43.239 STFC-RAL-CR03-RAL-R61-2.01: where the field has got to and what the challenges are. 413 00:43:43.590 --> 00:43:48.399 STFC-RAL-CR03-RAL-R61-2.01: and a few things that various people are doing to try and meet some of the challenges. 414 00:43:48.730 --> 00:43:52.260 STFC-RAL-CR03-RAL-R61-2.01: I'm not going to spend a long time on this. 415 00:43:53.380 --> 00:44:02.399 STFC-RAL-CR03-RAL-R61-2.01: So in terms of where we are making a GEV beam So a synchrotron kind of beam is sort of routine that's been done by many, many groups. 416 00:44:02.740 --> 00:44:03.720 STFC-RAL-CR03-RAL-R61-2.01: Those… 417 00:44:03.880 --> 00:44:17.309 STFC-RAL-CR03-RAL-R61-2.01: electron beams are being used to make radiation by the sorts of techniques you would normally use in a single form. So underlators, the beat of motion we've seen actually gives you quite hard X-rays up in tens or 100 kb range. 418 00:44:18.020 --> 00:44:19.130 STFC-RAL-CR03-RAL-R61-2.01: if you… 419 00:44:19.530 --> 00:44:30.899 STFC-RAL-CR03-RAL-R61-2.01: collide electron beam with a scattering laser pulse. You can do inverse competence scattering. So you can. You have a little tiny as an accelerator. It's probably making a few 100 Mev electrons. 420 00:44:30.980 --> 00:44:44.920 STFC-RAL-CR03-RAL-R61-2.01: You can use the same laser, split off a bit of the beam and collide it with electrons. You get a gamma squared shift in the wavelength. So you can get to photo energies of the 100 MV level and even beyond actually. 421 00:44:45.120 --> 00:44:46.070 STFC-RAL-CR03-RAL-R61-2.01: And… 422 00:44:46.420 --> 00:44:52.429 STFC-RAL-CR03-RAL-R61-2.01: And then recently, in the last few years, people have demonstrated free electoral mitigation. So this was a really big 423 00:44:52.560 --> 00:44:56.629 STFC-RAL-CR03-RAL-R61-2.01: Gold steel, Greg, always. 424 00:44:57.120 --> 00:45:02.350 STFC-RAL-CR03-RAL-R61-2.01: And the reason it's a goal is it's very hard, but if you need very good quality, that's a bunches. 425 00:45:02.580 --> 00:45:07.189 STFC-RAL-CR03-RAL-R61-2.01: and people just started to get there. So this 1st demonstration. 426 00:45:07.380 --> 00:45:13.740 STFC-RAL-CR03-RAL-R61-2.01: electrical gain at 27 nanometers. So that's sort of extreme ultraviolet. It's not a hard end for you. 427 00:45:14.270 --> 00:45:20.409 STFC-RAL-CR03-RAL-R61-2.01: So this is a big breakthrough. And we're going to see a lot more developments on those lines in the coming years. 428 00:45:21.150 --> 00:45:27.029 STFC-RAL-CR03-RAL-R61-2.01: But people are taking seriously enough to build new buildings. So the bank which I now got no idea where it is. But 429 00:45:27.310 --> 00:45:29.839 STFC-RAL-CR03-RAL-R61-2.01: Thoughts on this plane? 430 00:45:30.650 --> 00:45:40.210 STFC-RAL-CR03-RAL-R61-2.01: is is now finished almost, and it's going to start commissioning. And really, it's a resin deck is to to use these laser driven 431 00:45:40.710 --> 00:45:57.219 STFC-RAL-CR03-RAL-R61-2.01: beams for applications in imaging, etc, as well as development of themselves, but also to really start to get you around. It's very exciting. There's also a big European project to do something similar. 432 00:45:58.150 --> 00:45:59.020 STFC-RAL-CR03-RAL-R61-2.01: And. 433 00:45:59.460 --> 00:46:09.860 STFC-RAL-CR03-RAL-R61-2.01: But we're not, I hope, not too naive to realize that there are challenges around the whole field. This is probably an incomplete list. 434 00:46:10.010 --> 00:46:16.749 STFC-RAL-CR03-RAL-R61-2.01: You need better energy spread. The numbers I've got there are from the SUNYMASS white paper. 435 00:46:16.900 --> 00:46:20.120 STFC-RAL-CR03-RAL-R61-2.01: after the one with the asterisk, which I made up. 436 00:46:20.890 --> 00:46:21.990 STFC-RAL-CR03-RAL-R61-2.01: But you need… 437 00:46:22.630 --> 00:46:28.869 STFC-RAL-CR03-RAL-R61-2.01: For lots of applications, you need very narrow, narrow than we tend to get. The numbers there have all been achieved. 438 00:46:29.290 --> 00:46:32.610 STFC-RAL-CR03-RAL-R61-2.01: But not all at the same time. That's one of the few things. 439 00:46:33.810 --> 00:46:42.090 STFC-RAL-CR03-RAL-R61-2.01: We need public retrofittance, we need reproducibility, that's hard, right? At the moment, every time you fire your accelerator, you get a 5-year bunch, and that's a problem. 440 00:46:42.480 --> 00:46:58.380 STFC-RAL-CR03-RAL-R61-2.01: you probably also need to increase the repetition rate. It will say something about if you want to move towards a collider, you really need to worry about wall burn efficiency. And I haven't really mentioned positrons. So if you want to talk about bias, you probably need to bump into something. So you need to be positrons, too. 441 00:46:58.690 --> 00:47:02.580 STFC-RAL-CR03-RAL-R61-2.01: The sorts of things which are going to solve these problems are 442 00:47:03.960 --> 00:47:12.560 STFC-RAL-CR03-RAL-R61-2.01: controlling how you get the electrons into the right field. I've said nothing about that at all. There's a lot of work on it. There's lots of techniques which are being explored. 443 00:47:12.750 --> 00:47:20.570 STFC-RAL-CR03-RAL-R61-2.01: I still think it's an open question, the best way of doing that. But that will that will solve some of those challenges. 444 00:47:20.920 --> 00:47:33.170 STFC-RAL-CR03-RAL-R61-2.01: Increasing reproducibility will obviously lead to feedback and maybe machine learning, etc. Increasing the rep rate. Well, maybe that's new laser technology. Or maybe it's a new way of trying to drive the road. But I'm going to say a bit more about these last 2 things. 445 00:47:34.120 --> 00:47:38.380 STFC-RAL-CR03-RAL-R61-2.01: But just to show you that people are taking it seriously, I'm going to show you two results from Daisy. 446 00:47:38.730 --> 00:47:45.960 STFC-RAL-CR03-RAL-R61-2.01: And… This is work that's been done, I guess, over the last decade or so, using a beamline 447 00:47:46.110 --> 00:47:48.230 STFC-RAL-CR03-RAL-R61-2.01: Well, that's an important feature. 448 00:47:48.710 --> 00:47:55.219 STFC-RAL-CR03-RAL-R61-2.01: of that is, it's a B mine in the sense that they built it. They've kept refining it, getting better and better and better. 449 00:47:55.720 --> 00:48:06.169 STFC-RAL-CR03-RAL-R61-2.01: just as you would do with a with a proper accelerator rather than a sort of a short number of weeks. And then they're really improving it as they as they learn. 450 00:48:06.360 --> 00:48:11.449 STFC-RAL-CR03-RAL-R61-2.01: I mean, this… Set of results, what they were doing was they were measuring the 451 00:48:11.620 --> 00:48:16.359 STFC-RAL-CR03-RAL-R61-2.01: properties of the laser used to drive the accelerator at many points in the system. 452 00:48:16.810 --> 00:48:18.609 STFC-RAL-CR03-RAL-R61-2.01: Recording that data. 453 00:48:18.810 --> 00:48:26.210 STFC-RAL-CR03-RAL-R61-2.01: And they're running for long periods. So they in this run they ran for 24 h, which is a big deal for this field. 454 00:48:26.420 --> 00:48:33.249 STFC-RAL-CR03-RAL-R61-2.01: and measuring the energy electrons coming out because it's really beam winding, but lots of sort of beam transport stuff. Here's the spectrometer. 455 00:48:33.440 --> 00:48:36.000 STFC-RAL-CR03-RAL-R61-2.01: Just looking forward to MEB. 456 00:48:36.530 --> 00:48:43.369 STFC-RAL-CR03-RAL-R61-2.01: And then what they did is they measured the electrical energy as a function of some of the laser parameters. So this is the laser energy. 457 00:48:43.620 --> 00:48:47.569 STFC-RAL-CR03-RAL-R61-2.01: That's where the focus of the laser is relative to the start of the plasma. 458 00:48:47.860 --> 00:48:53.369 STFC-RAL-CR03-RAL-R61-2.01: The features are 20. Okay, they measured those things and then looked at the correlations. 459 00:48:53.920 --> 00:48:58.149 STFC-RAL-CR03-RAL-R61-2.01: of the output energy of the electron with respect to those parameters. 460 00:48:58.270 --> 00:49:01.539 STFC-RAL-CR03-RAL-R61-2.01: the 2 apples. And that's what this gray area is here. 461 00:49:01.720 --> 00:49:13.619 STFC-RAL-CR03-RAL-R61-2.01: This allowed them to figure out the coefficients, these coefficients, just the linear coefficients of those processes, and then you can predict what's going to happen for the rest of the run. 462 00:49:13.710 --> 00:49:28.790 STFC-RAL-CR03-RAL-R61-2.01: Okay, so the blue curve here is the measured electron energy, because it's wobbling around a bit, and the orange curve is what you predict once you've measured those coefficients, and you can see it agrees really quite well, and so the next step, of course, is you now have some 463 00:49:29.050 --> 00:49:32.799 STFC-RAL-CR03-RAL-R61-2.01: feedback on those things, and you should know what we managed. 464 00:49:33.950 --> 00:49:38.730 STFC-RAL-CR03-RAL-R61-2.01: and in a similar vein. They've recently done some work. 465 00:49:39.040 --> 00:49:45.720 STFC-RAL-CR03-RAL-R61-2.01: with an active energy stabilization which uses it should come in. 466 00:49:46.280 --> 00:49:48.270 STFC-RAL-CR03-RAL-R61-2.01: So you have your accelerator. 467 00:49:48.410 --> 00:49:57.229 STFC-RAL-CR03-RAL-R61-2.01: Here he's going to go through a chicane such that the high energy electrons come out at the front of the bunch, and so on through at the back. 468 00:49:57.730 --> 00:50:06.140 STFC-RAL-CR03-RAL-R61-2.01: You then squirt that into an expand cavity and set the timing right. So you're on the linear part of the field inside the cavity. 469 00:50:06.320 --> 00:50:17.219 STFC-RAL-CR03-RAL-R61-2.01: So that decelerates the fast electrons at the front and the speeds of ones up at the back, rotate the phase space, and you can see here the output energy goes from this sort of jumping around. 470 00:50:17.380 --> 00:50:20.740 STFC-RAL-CR03-RAL-R61-2.01: Behavior to being completely locked. 471 00:50:21.150 --> 00:50:35.770 STFC-RAL-CR03-RAL-R61-2.01: at the target energy. So the energy spread is reduced by more than a factor of 10, which is reduced to sort of point 0 5%. Okay? So you could. If you put everything you can make these things stable. I think this is also very important work. 472 00:50:37.160 --> 00:50:42.269 STFC-RAL-CR03-RAL-R61-2.01: Oh, yeah. So I've not really mentioned providers and drivers. 473 00:50:42.510 --> 00:50:50.369 STFC-RAL-CR03-RAL-R61-2.01: So I thought I would just show you a lot of work on that as well. It's not stuff I'm very familiar with, but my colleague Richard Darcy. 474 00:50:50.650 --> 00:50:59.209 STFC-RAL-CR03-RAL-R61-2.01: The Oxford is one of the proponents of the half scheme. So you. It's not given a Seminar. I'm sure I'd be happy to come and give one. 475 00:50:59.330 --> 00:51:00.100 STFC-RAL-CR03-RAL-R61-2.01: And. 476 00:51:00.450 --> 00:51:07.529 STFC-RAL-CR03-RAL-R61-2.01: And this is this is a sort of concept to imagine driving TV inside a Higgs factory with plasma. 477 00:51:07.640 --> 00:51:16.149 STFC-RAL-CR03-RAL-R61-2.01: and it sort of highlights one of the issues which is not something I've got into, which is the positron problem. 478 00:51:17.100 --> 00:51:22.710 STFC-RAL-CR03-RAL-R61-2.01: It's quite hard to tell a positron to this approach, at least in the nonlinear regime. 479 00:51:22.920 --> 00:51:32.710 STFC-RAL-CR03-RAL-R61-2.01: So they get around that by not doing it. And so they they accelerate the positrons. 480 00:51:33.470 --> 00:51:35.740 STFC-RAL-CR03-RAL-R61-2.01: Eventually, in this scheme. 481 00:51:36.270 --> 00:51:52.499 STFC-RAL-CR03-RAL-R61-2.01: and then use the plasma to do what it's best at, which is electrical, at least best at the moment. Let's say that so I won't go into too much detail. But this sort of conventional accelerator here, that's that's accelerating positrons to 42 Gv. 482 00:51:52.700 --> 00:51:57.470 STFC-RAL-CR03-RAL-R61-2.01: And then these are plasma accelerators. I think we have 48 stages. 483 00:51:57.630 --> 00:52:02.329 STFC-RAL-CR03-RAL-R61-2.01: Gets you up to 200 and… sorry, 375 GB. 484 00:52:02.690 --> 00:52:15.780 STFC-RAL-CR03-RAL-R61-2.01: in a relatively short distance, and then you collide them here. But it's an asymmetric collider. So the 2 beams don't have the same energy, but the center of mass energy is 250 Gv, I think. So. 485 00:52:15.870 --> 00:52:25.839 STFC-RAL-CR03-RAL-R61-2.01: and it's obviously high rep rate, etc. And the idea is relatively small, so 2 kilometers, and the cost will be relatively low. So this is now 486 00:52:26.230 --> 00:52:29.470 STFC-RAL-CR03-RAL-R61-2.01: estimated at around half the cost of click something. So 487 00:52:29.740 --> 00:52:40.549 STFC-RAL-CR03-RAL-R61-2.01: It's a very serious effort to to really think about the hard problems you would have to solve to drive gliders. But I think people still really appreciate. Believe there's still very hot problems. 488 00:52:40.720 --> 00:52:43.389 STFC-RAL-CR03-RAL-R61-2.01: So that's just a sort of outlook, if you will. 489 00:52:44.120 --> 00:52:50.610 STFC-RAL-CR03-RAL-R61-2.01: Okay, so I'm gonna just spend maybe 5 min to say if I can. Another thing we're looking at, which is 490 00:52:50.810 --> 00:52:56.570 STFC-RAL-CR03-RAL-R61-2.01: How could we increase the refrigeration rate of the lace? So The, quote limits… 491 00:52:56.710 --> 00:53:02.280 STFC-RAL-CR03-RAL-R61-2.01: The pulse rate at the moment is the fact that the lasers which are used are not very efficient. 492 00:53:02.680 --> 00:53:17.469 STFC-RAL-CR03-RAL-R61-2.01: So nearly all of the energy you put into exciting the gain medium in the laser comes out as heat eventually. And so that's problematic. And it means that these systems are typically one hertz or maybe 10. 493 00:53:17.560 --> 00:53:28.860 STFC-RAL-CR03-RAL-R61-2.01: we'd like to sort of run these things at Kilohertz, because lots of applications would probably benefit from that, and also make better use of feedback systems, etc. And it's a sort of challenge which we think is 494 00:53:29.350 --> 00:53:34.180 STFC-RAL-CR03-RAL-R61-2.01: difficult, but maybe not stupidly impossible. So that's a sort of target we're aiming at. 495 00:53:35.430 --> 00:53:39.050 STFC-RAL-CR03-RAL-R61-2.01: And so this is our approach. 496 00:53:40.340 --> 00:53:51.770 STFC-RAL-CR03-RAL-R61-2.01: plasma modulated plasma accelerator. The it builds on the following observation, which is that you can buy lasers that run at one kilohertz that deliver joules of laser energy. 497 00:53:52.020 --> 00:54:00.320 STFC-RAL-CR03-RAL-R61-2.01: at the right average power, if you will. But if it's too long, about a piece a second long, you might remember we can get delayed a lot shorter than the question period. 498 00:54:00.730 --> 00:54:02.789 STFC-RAL-CR03-RAL-R61-2.01: So the question is, could we find a way 499 00:54:03.020 --> 00:54:09.119 STFC-RAL-CR03-RAL-R61-2.01: but modulating these bulks so that they could drive away, and if we could, but then suddenly have a killer. 500 00:54:09.930 --> 00:54:10.840 STFC-RAL-CR03-RAL-R61-2.01: Umm. 501 00:54:11.430 --> 00:54:12.950 STFC-RAL-CR03-RAL-R61-2.01: It's a difficult scheme. 502 00:54:13.520 --> 00:54:14.960 STFC-RAL-CR03-RAL-R61-2.01: Let's go 3 steps. 503 00:54:15.290 --> 00:54:21.339 STFC-RAL-CR03-RAL-R61-2.01: The first is, you take one of these Opie channels, the optical channels we've developed. 504 00:54:21.500 --> 00:54:29.569 STFC-RAL-CR03-RAL-R61-2.01: And you put into it a short pulse with not too much energy, so maybe 100 milli. So that's a doable thing. 505 00:54:29.810 --> 00:54:46.619 STFC-RAL-CR03-RAL-R61-2.01: kilohertz, and its job is to drive the wake field, which is very low energy, 81% energy. So density variations. Then right behind it, you have a jewel or more of drive energy from one of these in this phase of 506 00:54:47.580 --> 00:54:52.070 STFC-RAL-CR03-RAL-R61-2.01: which is people's economic. They they co-propagate through 507 00:54:52.400 --> 00:54:59.740 STFC-RAL-CR03-RAL-R61-2.01: the channel, the long content sitting on top of the person wave that develops sidebands in frequency space. 508 00:55:00.770 --> 00:55:09.010 STFC-RAL-CR03-RAL-R61-2.01: So the spectrum coming out will have sideband space by an omega p. That's a sort of consequence of sitting on something which is modulated. 509 00:55:09.490 --> 00:55:10.250 STFC-RAL-CR03-RAL-R61-2.01: Okay. 510 00:55:10.730 --> 00:55:17.999 STFC-RAL-CR03-RAL-R61-2.01: So then you remove any phase on these sidebands. They'll have a relative phase. We think we know what it is. 511 00:55:18.340 --> 00:55:27.240 STFC-RAL-CR03-RAL-R61-2.01: And then by Fourier transform theory, you've got a comb of frequencies, you can flatten phase, you get a comb in time space, and so you get a comb of pulses. 512 00:55:27.860 --> 00:55:33.350 STFC-RAL-CR03-RAL-R61-2.01: These would be spaced by the placement period by definitions. 513 00:55:33.470 --> 00:55:38.200 STFC-RAL-CR03-RAL-R61-2.01: So if you focus that into a second channel, the third stage here. 514 00:55:38.540 --> 00:55:46.009 STFC-RAL-CR03-RAL-R61-2.01: The density of this thing matches the density of that thing. Then you can resonantly excite a large amplitude. 515 00:55:47.350 --> 00:55:56.800 STFC-RAL-CR03-RAL-R61-2.01: So we're slowly working our way through testing these concepts. And I'm just going to show you some results we did here on the last stage called the accelerator stage. 516 00:55:56.930 --> 00:56:00.630 STFC-RAL-CR03-RAL-R61-2.01: which we did with the Gemini laser a couple of years ago. 517 00:56:01.170 --> 00:56:02.110 STFC-RAL-CR03-RAL-R61-2.01: Umm. 518 00:56:02.730 --> 00:56:17.270 STFC-RAL-CR03-RAL-R61-2.01: So the Gemini laser is the wrong kind of laser for this. It's not a thin disc laser. So we took one of the laser pulses from Gemini and made a train of them. So we developed a technique for doing that which I won't go into. So one laser pulse becomes a train. 519 00:56:17.560 --> 00:56:18.500 STFC-RAL-CR03-RAL-R61-2.01: You see it. 520 00:56:18.680 --> 00:56:19.440 STFC-RAL-CR03-RAL-R61-2.01: Yep. 521 00:56:19.860 --> 00:56:26.920 STFC-RAL-CR03-RAL-R61-2.01: And then we focus it into one of these channels. This is the channel forming pulse. This is a sort of gas cell, 100 millimeters long, I'll say. 522 00:56:27.060 --> 00:56:32.840 STFC-RAL-CR03-RAL-R61-2.01: And then we were looking for evidence that we could resonantly excite a strong lake with this 523 00:56:33.210 --> 00:56:34.800 STFC-RAL-CR03-RAL-R61-2.01: Training courses. 524 00:56:36.230 --> 00:56:42.620 STFC-RAL-CR03-RAL-R61-2.01: So the diagnostic is very easy to just take the spectrum of the train as it comes through the plasma. 525 00:56:42.970 --> 00:56:45.080 STFC-RAL-CR03-RAL-R61-2.01: This is the input spectrum. 526 00:56:45.590 --> 00:56:49.399 STFC-RAL-CR03-RAL-R61-2.01: It's modulated because of the way we chopped it up to make the train. 527 00:56:49.800 --> 00:56:59.229 STFC-RAL-CR03-RAL-R61-2.01: If you then put an arbitrary plasma in the channel, some arbitrary density, you get a spectrum like this coming out, which in other words, it's not really changed very much. 528 00:57:00.380 --> 00:57:04.559 STFC-RAL-CR03-RAL-R61-2.01: It's a little bit weak on the blue, but this is what we can talk about. 529 00:57:04.740 --> 00:57:12.500 STFC-RAL-CR03-RAL-R61-2.01: But if you tune the density just right, you get this, you see very, very strong Richard did. 530 00:57:12.620 --> 00:57:16.540 STFC-RAL-CR03-RAL-R61-2.01: of the spectrum. The redshift thing tells you you've put energy into the vessel. 531 00:57:17.680 --> 00:57:19.830 STFC-RAL-CR03-RAL-R61-2.01: So you do this many times. 532 00:57:20.050 --> 00:57:26.719 STFC-RAL-CR03-RAL-R61-2.01: And you can see, as you change the electrical density in this plot, these are raw spectra, and you can see, you see the broadening that there's here. 533 00:57:26.850 --> 00:57:32.159 STFC-RAL-CR03-RAL-R61-2.01: in that region. This is just reducing the data somewhat. You can see that the resonance 534 00:57:32.400 --> 00:57:36.529 STFC-RAL-CR03-RAL-R61-2.01: At this density, which is exactly where you'd expect the residents to occur. 535 00:57:37.050 --> 00:57:42.580 STFC-RAL-CR03-RAL-R61-2.01: Then, if you do some simulation, reproduce that you can pull out the 536 00:57:42.820 --> 00:57:49.700 STFC-RAL-CR03-RAL-R61-2.01: accelerating field you've got in the past the way that you've been driving. And in this this work we find that it's 537 00:57:50.130 --> 00:57:54.519 STFC-RAL-CR03-RAL-R61-2.01: an energy gain from one end of the stage to the other between point 3 and one Gp. 538 00:57:54.710 --> 00:57:57.349 STFC-RAL-CR03-RAL-R61-2.01: So it's sort of Gv scale space. So 539 00:57:58.190 --> 00:58:06.780 STFC-RAL-CR03-RAL-R61-2.01: We're very confident this works if we can make the trains right. So we're continuing to work with colleagues in Munich on the first part. 540 00:58:08.090 --> 00:58:10.200 STFC-RAL-CR03-RAL-R61-2.01: So I'll wrap up. 541 00:58:10.760 --> 00:58:12.890 STFC-RAL-CR03-RAL-R61-2.01: So I hope I've convinced you. 542 00:58:13.000 --> 00:58:17.700 STFC-RAL-CR03-RAL-R61-2.01: that these systems can give very high gradients. 543 00:58:17.840 --> 00:58:24.419 STFC-RAL-CR03-RAL-R61-2.01: Acceleration… They're sort of… Applications starting to emerge, mainly around light generation. 544 00:58:24.600 --> 00:58:28.260 STFC-RAL-CR03-RAL-R61-2.01: Which I think is really interesting. 545 00:58:29.230 --> 00:58:37.130 STFC-RAL-CR03-RAL-R61-2.01: continues to develop as greatly as we. But we know that there are many, many problems which need to be solved. These things become 546 00:58:37.530 --> 00:58:52.479 STFC-RAL-CR03-RAL-R61-2.01: realistic drivers of various demanding applications. So people in this room aren't interested in. And there's a lot of work aimed at solving those problems. But you know, it's gonna take time for the challenge. So with that, I'd like to read everything. 547 00:58:57.060 --> 00:59:04.250 STFC-RAL-CR03-RAL-R61-2.01: It… Thank you very much for a very nice and interesting talk. Are there questions? 548 00:59:07.640 --> 00:59:23.169 STFC-RAL-CR03-RAL-R61-2.01: Yes. Hi. Thank you very much for the very nice overview. I just wanted to ask, why are you using the blue spectrum in the platform? Yeah, so that's because the blue was at the front of the laser pulse. 549 00:59:25.220 --> 00:59:27.010 STFC-RAL-CR03-RAL-R61-2.01: So 550 00:59:27.710 --> 00:59:41.559 STFC-RAL-CR03-RAL-R61-2.01: because of the way we made it. We look carefully this diagram. We made these trays by using the spectrum width of each type of alcohol, so effectively chirped it to the blue to the front of the blood and the red at the back. 551 00:59:41.890 --> 00:59:52.939 STFC-RAL-CR03-RAL-R61-2.01: and we pass it through a filter which only lets you set the frequencies right? And so the blues at the front. And that's these pulses here. Some of those pulses are lost because they're ionizing this column. 552 00:59:53.360 --> 00:59:55.819 STFC-RAL-CR03-RAL-R61-2.01: On the outside, the channel's not quite formed. 553 00:59:56.080 --> 01:00:01.040 STFC-RAL-CR03-RAL-R61-2.01: And so the the the transcripts as well as the link. 554 01:00:01.620 --> 01:00:03.040 STFC-RAL-CR03-RAL-R61-2.01: But that's a good example. 555 01:00:04.700 --> 01:00:05.450 STFC-RAL-CR03-RAL-R61-2.01: Oh. 556 01:00:08.910 --> 01:00:17.900 STFC-RAL-CR03-RAL-R61-2.01: So I mean in terms of the form factor for a 2 GV electron beam. How big 557 01:00:18.140 --> 01:00:21.130 STFC-RAL-CR03-RAL-R61-2.01: The whole system will be going. 558 01:00:21.720 --> 01:00:23.860 STFC-RAL-CR03-RAL-R61-2.01: Umm. 559 01:00:25.000 --> 01:00:26.390 STFC-RAL-CR03-RAL-R61-2.01: 2GB… 560 01:00:28.640 --> 01:00:46.400 STFC-RAL-CR03-RAL-R61-2.01: What do you think? You can fit it in two rooms. You can, I mean, for 2G, you need to make a jewel also, something like that, maybe. A couple of rooms this size, something like this. A couple of rooms this size, okay. And, I mean, yes, you might need all the dimensions. Yeah. And, 561 01:00:47.230 --> 01:00:53.350 STFC-RAL-CR03-RAL-R61-2.01: Can we excite a neutron beam? 562 01:00:53.760 --> 01:00:54.780 STFC-RAL-CR03-RAL-R61-2.01: Thanks. 563 01:00:55.400 --> 01:01:13.960 STFC-RAL-CR03-RAL-R61-2.01: Really nice talk, Simon. The question I have is, with the Hofe, not the Hofe, the Half, idea, we're going to have many stages there. Yes. And that, that is, I mean, we've got a big challenge there. You, you just, sort of. 564 01:01:14.070 --> 01:01:20.060 STFC-RAL-CR03-RAL-R61-2.01: So mentioned it in passing. The staging is big problem. 565 01:01:20.480 --> 01:01:26.160 STFC-RAL-CR03-RAL-R61-2.01: And have you any ideas apart from the flying focus to get away from the staging problem? 566 01:01:26.410 --> 01:01:27.350 STFC-RAL-CR03-RAL-R61-2.01: And 567 01:01:28.820 --> 01:01:41.450 STFC-RAL-CR03-RAL-R61-2.01: Well, there's a lot hidden in that question. So staging in some ways is more of a problem for the Layston case. 568 01:01:42.810 --> 01:01:45.970 STFC-RAL-CR03-RAL-R61-2.01: Well, maybe that's not true. 569 01:01:46.840 --> 01:01:51.969 STFC-RAL-CR03-RAL-R61-2.01: Yeah. So you need, you need to sort of glue. 570 01:01:52.350 --> 01:02:04.099 STFC-RAL-CR03-RAL-R61-2.01: sections ago. But you do that anyway, in a virtual machine. So I think I'm not responsible for that. But I think the approach there is looking at there would be the same. 571 01:02:04.530 --> 01:02:10.999 STFC-RAL-CR03-RAL-R61-2.01: There is a… on the later side, There is a very interesting 572 01:02:11.720 --> 01:02:26.330 STFC-RAL-CR03-RAL-R61-2.01: alternative approach, which is, instead of running to be phasing, then you have to sort of stop the acceleration. You have to start another one. But that's that's the approach most people are looking at. You can. You can. 573 01:02:26.620 --> 01:02:30.579 STFC-RAL-CR03-RAL-R61-2.01: Manipulate the nose spots in such a way that effectively control its velocity. 574 01:02:31.000 --> 01:02:37.219 STFC-RAL-CR03-RAL-R61-2.01: And you can make them go at sea, even at Kaiser, because it's a difficult decline focus. 575 01:02:38.040 --> 01:02:43.529 STFC-RAL-CR03-RAL-R61-2.01: the it's really interesting stuff. The thing I'm not 100% sure about is how efficient it is, because 576 01:02:43.820 --> 01:02:54.979 STFC-RAL-CR03-RAL-R61-2.01: each section. What you're doing is effectively focusing at different times along the axis. So this falls at the right moment. 577 01:02:55.190 --> 01:03:06.620 STFC-RAL-CR03-RAL-R61-2.01: So each little bit of laser pulse is somehow interacting with, let's say, a millimeter of buzz or something short, and then it more or less comes out because it's actually using something a bit like vessel. 578 01:03:07.640 --> 01:03:11.949 STFC-RAL-CR03-RAL-R61-2.01: I'm not sure how efficient this thing sometimes is, but it's really interesting, you know. 579 01:03:12.190 --> 01:03:14.609 STFC-RAL-CR03-RAL-R61-2.01: Yes, I agree with that. 580 01:03:14.880 --> 01:03:20.279 STFC-RAL-CR03-RAL-R61-2.01: We also need much higher energy because it's also chromatically. 581 01:03:20.390 --> 01:03:25.050 STFC-RAL-CR03-RAL-R61-2.01: Yeah, yeah. 582 01:03:26.660 --> 01:03:33.119 STFC-RAL-CR03-RAL-R61-2.01: Okay, first. Won Jung had his hand up. First, it was here. Okay. 583 01:03:33.410 --> 01:03:37.980 STFC-RAL-CR03-RAL-R61-2.01: So quick question by comparison with 584 01:03:38.510 --> 01:03:43.759 STFC-RAL-CR03-RAL-R61-2.01: You don't need a compressing the 2 picosecond post to do 10 to 20 seconds. 585 01:03:44.160 --> 01:03:46.349 STFC-RAL-CR03-RAL-R61-2.01: I mean, wouldn't that be more efficient? 586 01:03:47.230 --> 01:03:51.629 STFC-RAL-CR03-RAL-R61-2.01: And the other thing is stability, right? Which one would be most likely? Yeah. 587 01:03:52.030 --> 01:03:58.890 STFC-RAL-CR03-RAL-R61-2.01: That's a very good point. So these giga second policies we're looking at We were already impressed. 588 01:03:59.040 --> 01:04:01.620 STFC-RAL-CR03-RAL-R61-2.01: a bit of it to make a sequence. 589 01:04:01.970 --> 01:04:05.910 STFC-RAL-CR03-RAL-R61-2.01: So we take about 100 individuals and press it down to 590 01:04:06.870 --> 01:04:10.260 STFC-RAL-CR03-RAL-R61-2.01: So give me 30 seconds. It's actually But, 591 01:04:11.000 --> 01:04:17.690 STFC-RAL-CR03-RAL-R61-2.01: In order to do that, you have to pass an ice pulse repeatedly through a lot of gas. 592 01:04:17.960 --> 01:04:28.950 STFC-RAL-CR03-RAL-R61-2.01: at a high intensity, and that spectrum broadens it through a nonlinear process. And if you've got more spectrum, you can then compress it to shorter holes. And so that's a very interesting way of doing it. 593 01:04:29.330 --> 01:04:37.799 STFC-RAL-CR03-RAL-R61-2.01: The… in order to compress 100 millijoules, we need a gas cell, and things pass through about 24 tons of it. 594 01:04:38.200 --> 01:04:40.310 STFC-RAL-CR03-RAL-R61-2.01: 48, I don't remember. 595 01:04:40.870 --> 01:04:42.659 STFC-RAL-CR03-RAL-R61-2.01: It's 24 minutes of each end. 596 01:04:43.360 --> 01:04:45.090 STFC-RAL-CR03-RAL-R61-2.01: and this is 8 meters long. 597 01:04:46.230 --> 01:04:47.870 STFC-RAL-CR03-RAL-R61-2.01: And, 598 01:04:48.150 --> 01:04:55.309 STFC-RAL-CR03-RAL-R61-2.01: I can't remember how it scales, so you can't have the density up, but you have to sort of keep the look of the focus spot size the same. If you've got too much density, it just ionizes. 599 01:04:55.540 --> 01:05:13.810 STFC-RAL-CR03-RAL-R61-2.01: And so if you want to go to Joule, it's going to have to be 10 times longer, or… Yeah, so this… I mean, it will have to be solids, right? So it will have to be a… Yeah. You know, you're right, it couldn't be in a… it could have to be in solids in a vacuum. Yeah, yeah, it may be that, like, if someone could do that, then that's not a problem, I think so. Okay. 600 01:05:15.750 --> 01:05:27.350 STFC-RAL-CR03-RAL-R61-2.01: I don't think anyone's I think the record is about 100 million jobs, maybe maybe 200. And those are Georgia. It's just really hard. But yeah, it's getting it. 601 01:05:28.080 --> 01:05:30.520 STFC-RAL-CR03-RAL-R61-2.01: One question. 602 01:05:33.340 --> 01:05:34.110 STFC-RAL-CR03-RAL-R61-2.01: Okay. 603 01:05:34.440 --> 01:05:40.920 STFC-RAL-CR03-RAL-R61-2.01: Yeah, thank you for the wonderful talk about this topic. So I was actually curious if. 604 01:05:41.280 --> 01:05:46.090 STFC-RAL-CR03-RAL-R61-2.01: If this idea could be applied to protons or other heavy particles as well. 605 01:05:46.500 --> 01:06:05.859 STFC-RAL-CR03-RAL-R61-2.01: Is it like vastly different because it's not, it can reach like that ballistic energy which means it's electrons where is there other like kind of pieces. Yeah, that's a very good question. And people have also like muons as well. The issue, as you said in your question, is that the wake field goes at the speed of light. 606 01:06:06.840 --> 01:06:12.390 STFC-RAL-CR03-RAL-R61-2.01: at least naively. It's already got to be relativistic before you can really catch the way. 607 01:06:13.860 --> 01:06:27.169 STFC-RAL-CR03-RAL-R61-2.01: So the protons a thousand times more on it. So it's sort of very relevant. Now, the sorts of things people are doing with these like foci. 608 01:06:27.780 --> 01:06:41.049 STFC-RAL-CR03-RAL-R61-2.01: could be a way forward because you can slow the velocity of the basal stands. And if it's such an interesting idea, maybe you can slow it down just to get an optimal. I think most people would say. 609 01:06:41.160 --> 01:06:44.780 STFC-RAL-CR03-RAL-R61-2.01: But right now, it's… That's a little challenging. 610 01:06:45.200 --> 01:06:52.029 STFC-RAL-CR03-RAL-R61-2.01: and probably the next time you see me, you'll feel very tired. 611 01:06:52.920 --> 01:07:12.440 STFC-RAL-CR03-RAL-R61-2.01: Yes, they'll be 200 times more massive than the electrons. I mean, they're fine focus. But the other thing is, you can modulate electron beam laser beams that are going group speed. 612 01:07:12.630 --> 01:07:20.149 STFC-RAL-CR03-RAL-R61-2.01: Yeah. At the muon speed, so you can actually get them up to show them. 613 01:07:20.600 --> 01:07:31.499 STFC-RAL-CR03-RAL-R61-2.01: Thank you very much. Thanks. So what do I kind of accomplish with it? Really, really clear summary. 614 01:07:31.720 --> 01:07:34.549 STFC-RAL-CR03-RAL-R61-2.01: not who's where to look for a lot. My my 615 01:07:35.020 --> 01:07:42.039 STFC-RAL-CR03-RAL-R61-2.01: Question is, it's not all about science. And you made a great case, I think, for the unique kind of beans. 616 01:07:42.200 --> 01:07:48.709 STFC-RAL-CR03-RAL-R61-2.01: Certainly the the X-ray application and then the acceleration short. 617 01:07:48.950 --> 01:07:55.910 STFC-RAL-CR03-RAL-R61-2.01: But the other… so, and that's about investment cost. The run thing is now about the power. 618 01:07:56.030 --> 01:08:03.680 STFC-RAL-CR03-RAL-R61-2.01: Hello? So… What's the comparison there? Is that, still good? 619 01:08:04.600 --> 01:08:06.510 STFC-RAL-CR03-RAL-R61-2.01: I, I, yeah, I think it… 620 01:08:06.770 --> 01:08:25.770 STFC-RAL-CR03-RAL-R61-2.01: could be so right now, deeply inefficient. But they don't really need. But the index phases are much more, much less 10 to 30% efficient. 621 01:08:25.960 --> 01:08:29.400 STFC-RAL-CR03-RAL-R61-2.01: And that's not a long way, in my understanding. 622 01:08:29.399 --> 01:08:51.050 STFC-RAL-CR03-RAL-R61-2.01: Is that document, you know? Is that written down somewhere, or is it? Yeah, it's worth studying. Yeah, I think I think it's a lot of people looking at it, mostly not from an accelerated perspective, but from fusion perspective. So this is a bigger, bigger issue, right? Because you need to have. If you, if you spend a lot of energy 623 01:08:51.050 --> 01:08:54.889 STFC-RAL-CR03-RAL-R61-2.01: And what you, what you get out, then that's not really a… 624 01:08:55.000 --> 01:08:58.980 STFC-RAL-CR03-RAL-R61-2.01: Yes this is I mean as Sam said 625 01:08:59.080 --> 01:09:06.749 STFC-RAL-CR03-RAL-R61-2.01: new technologies are evolving. But eventually it does come down to how much energy you couple into plasma. 626 01:09:07.010 --> 01:09:15.989 STFC-RAL-CR03-RAL-R61-2.01: which is what Walter later later, the person for that principle. 627 01:09:16.040 --> 01:09:29.480 STFC-RAL-CR03-RAL-R61-2.01: But I think laser to electrons is already measured. So the overall efficiency, if you can fix the laser. 628 01:09:29.960 --> 01:09:39.769 STFC-RAL-CR03-RAL-R61-2.01: Well, the question, when compressing it using ZPA, what sort of pulse length are we going from? 629 01:09:40.880 --> 01:09:46.850 STFC-RAL-CR03-RAL-R61-2.01: roughly, and a second. 630 01:09:48.620 --> 01:09:56.840 STFC-RAL-CR03-RAL-R61-2.01: I wonder if possibly Okay. 631 01:09:57.400 --> 01:10:01.820 STFC-RAL-CR03-RAL-R61-2.01: It's really limited by… as Simon said. 632 01:10:02.270 --> 01:10:06.450 STFC-RAL-CR03-RAL-R61-2.01: How much money you want to spend on optics? 633 01:10:10.640 --> 01:10:13.179 STFC-RAL-CR03-RAL-R61-2.01: I have questions. On Zoom? 634 01:10:13.730 --> 01:10:15.680 STFC-RAL-CR03-RAL-R61-2.01: But no comments, nothing. 635 01:10:18.100 --> 01:10:22.929 STFC-RAL-CR03-RAL-R61-2.01: Okay, great. I think we can wrap up, and thanks, Simon. 636 01:10:25.170 --> 01:10:26.050 STFC-RAL-CR03-RAL-R61-2.01: Okay. 637 01:10:26.990 --> 01:10:27.690 STFC-RAL-CR03-RAL-R61-2.01: Okay. 638 01:10:29.570 --> 01:10:30.270 STFC-RAL-CR03-RAL-R61-2.01: Okay. 639 01:10:34.980 --> 01:10:48.289 STFC-RAL-CR03-RAL-R61-2.01: I don't know. 640 01:10:48.290 --> 01:10:57.810 STFC-RAL-CR03-RAL-R61-2.01: That's why we have been arranging the seminar.