1 00:00:15,990 --> 00:00:21,990 Thanks to everybody for giving up some of your time on a Saturday to come out and say a few words about fusion. 2 00:00:22,650 --> 00:00:30,180 So whenever we were first organising this event a couple of months ago, it was just at the time that GPT was exploding on to the scene. 3 00:00:30,630 --> 00:00:39,810 And I, like I'm guessing many of the people in this room spent some small amount of my time playing around with it and seeing what it was capable of. 4 00:00:40,410 --> 00:00:43,860 And that all culminated in the title for our talk today. 5 00:00:44,250 --> 00:00:47,310 So this is one of the things that I asked GPT three. 6 00:00:47,370 --> 00:00:52,860 I said, well, you know, give me a nice interesting title for a public lecture on fusion and, and this was the result. 7 00:00:54,600 --> 00:00:56,640 Although it wasn't the only one that almost made it in. 8 00:00:56,670 --> 00:01:02,490 Here are a few of the honourable mentions that I came up with, so quite a few of these I was quite happy with. 9 00:01:03,840 --> 00:01:09,090 So, you know, whether or not the future of AI is to become the salvation of humanity, 10 00:01:09,090 --> 00:01:13,670 its downfall, or just a footnote in history, at least we'll have this moment. 11 00:01:13,680 --> 00:01:22,290 Right? So getting on to Fusion, whether or not you're aware of it, most of the energy on Earth already comes from fusion. 12 00:01:22,500 --> 00:01:27,150 Right. And it's a bit sneaky, but that's because most of the fusion energy on Earth comes from the sun. 13 00:01:27,840 --> 00:01:33,140 And the sun delivers about. What is it? 44. 14 00:01:33,500 --> 00:01:40,820 Well, at the time it's 4.4 times ten to the 16 watts of fusion on average to the Earth's surface. 15 00:01:41,420 --> 00:01:47,210 That's a lot of zeroes. And so to put things in context that something like 44 million of our gigawatt power plants, 16 00:01:47,510 --> 00:01:50,899 and so we harvest a very small amount of that energy over time. 17 00:01:50,900 --> 00:01:56,270 So some of it directly by a solar energy, some of it indirectly by other means. 18 00:01:56,660 --> 00:02:01,610 So, for instance, the uneven heating of the atmosphere leads to wind that powers our wind turbines. 19 00:02:02,300 --> 00:02:09,680 We also have biomass, which is fuelled by the sun's energy, and this ultimately eats the fossils and the fossil fuels. 20 00:02:09,980 --> 00:02:18,530 So fusion works already. What we're trying to do is cut out the middleman and get fusion to work here in the labs on earth. 21 00:02:18,530 --> 00:02:20,550 And so we can hear two different approaches to that today. 22 00:02:21,440 --> 00:02:25,760 One that I'll talk about in Georgia we'll talk about and one that [INAUDIBLE] talk about at the end. 23 00:02:27,950 --> 00:02:32,120 But the common theme is here is that to get the fusion energy out, we need the fusion reaction. 24 00:02:32,660 --> 00:02:38,720 This is probably set a lot of you know, but the idea behind fusion is that were going to take two light elements. 25 00:02:39,170 --> 00:02:43,760 If you bring those light elements close enough together, then they're going to fuse. 26 00:02:44,060 --> 00:02:49,520 We're going to focus on one particular fusion reaction here today. Turns out to be the easiest for us to achieve in a lab. 27 00:02:49,910 --> 00:02:53,450 That's between two different ions of hydrogen called deuterium and tritium. 28 00:02:54,350 --> 00:03:00,620 When you bring them together and they fuse, you get these two products out, you get a helium ion and a neutron. 29 00:03:01,430 --> 00:03:08,990 And as is well known now from Einstein's famous equivalence of mass and energy, if, as it turns out, 30 00:03:09,050 --> 00:03:16,820 these products have less mass than what goes into it, an energy must have been moved into some other form, in this case into kinetic energy. 31 00:03:17,420 --> 00:03:22,580 So the leftover energy is about 17.6 metres of energy. 32 00:03:23,120 --> 00:03:28,850 And this reaction, which is about 10 million times as much energy that comes out of gas combustion. 33 00:03:29,060 --> 00:03:35,600 So there's a huge amount of energy here. And it turns out that the products aren't too difficult to find. 34 00:03:36,170 --> 00:03:39,889 The deuterium is readily harvested from seawater. 35 00:03:39,890 --> 00:03:44,930 So that's not the big issue. The tritium is not naturally occurring, at least not in large amounts. 36 00:03:45,140 --> 00:03:52,520 And so we have to breed the tritium by bombarding enriched lithium with a neutron that it gives our tritium and some energy out. 37 00:03:53,510 --> 00:03:59,450 Though this process is limited by the amount of lithium that's going to be available and the different ways they estimate it. 38 00:03:59,450 --> 00:04:04,760 But they come up to something like 20,000 years. So the hope is if we can get fusion to work, 39 00:04:05,420 --> 00:04:10,370 then it's going to give us a huge amount of energy and there's a lot of fuels that's going to last us for a long time. 40 00:04:13,800 --> 00:04:20,280 And so there are two main approaches to doing this. One of them called the Inertial Confinement Fusion Art he's going to talk about later. 41 00:04:20,580 --> 00:04:25,740 George and I are going to talk about a version of thermonuclear fusion, which is the way the sun works. 42 00:04:26,410 --> 00:04:31,260 Right. And so the problem that we have is if we're going to take two of these hydrogen 43 00:04:31,260 --> 00:04:34,860 ions and we want to bring them very close together for fusion to happen. 44 00:04:36,150 --> 00:04:41,940 But to do that, you have to overcome the natural tendency of these light charges to repel one another due to the Coulomb force. 45 00:04:42,360 --> 00:04:46,920 And so the we the way that we do this in thermonuclear fusion is we basically just heat the gas up really, really hot. 46 00:04:47,860 --> 00:04:49,009 So if you heated up hot enough, 47 00:04:49,010 --> 00:04:54,360 then the random thermal motion of these particles become sufficiently fast that the particles occasionally can come very close to one another, 48 00:04:54,660 --> 00:04:57,540 overcome the Coulomb barrier and fuse. 49 00:04:58,140 --> 00:05:03,520 Now it turns out the temperature you need to do that for this deuterium tritium reaction is about 100 million degrees. 50 00:05:04,140 --> 00:05:11,680 So that's hotter than the hottest parts of the sun. So how are we going to get this to work? 51 00:05:11,770 --> 00:05:18,580 There are clearly a couple of issues that we have to overcome. One of them is the fact that, you know, we eat something up hot in the sun. 52 00:05:18,590 --> 00:05:21,130 How are we going to do that? So how do we put the energy in to begin with? 53 00:05:21,670 --> 00:05:26,499 And the second challenge that we definitely have to overcome is how do we keep this thing insulated long enough, 54 00:05:26,500 --> 00:05:30,790 keep the energy in enough fusion reactions occur to harvest the energy. 55 00:05:31,330 --> 00:05:33,480 I should point out as a side note that at this temperature, 56 00:05:33,610 --> 00:05:39,280 way below this temperature at about 10,000 degrees, this gas becomes ionised and turns into a plasma. 57 00:05:39,280 --> 00:05:43,210 So everything going to be looking at here is an ionised gas called the plasma. 58 00:05:45,680 --> 00:05:51,350 So how are we going to do this? Well, the basic idea behind magnetic confinement, fusion, which is what I'll be describing, 59 00:05:51,560 --> 00:05:55,850 is to take magnetic field lines and wrap them around our plasma and keep all the energy in. 60 00:05:56,390 --> 00:06:02,990 And this way. So what I'm going to try to convince you of here in this slide is that our aim is roughly, 61 00:06:02,990 --> 00:06:11,300 very roughly speaking, to get one gram of this hydrogen ions at about 100 million degrees for about a second. 62 00:06:12,860 --> 00:06:20,480 And the physics behind it is pretty simple. What we're saying is that we have some fusion power which is being created in our plasma. 63 00:06:20,840 --> 00:06:27,530 And what we need for this to be self-sustaining is that to at least balance the rate at which the energy is leaving the plasma. 64 00:06:27,860 --> 00:06:34,310 And so we have some thermal energy density here divided by the time it takes for that thermal energy to leave our plasma. 65 00:06:34,360 --> 00:06:36,980 And that's got to balance the rate at which the energy is going in. 66 00:06:38,710 --> 00:06:43,330 So the power delivered by fusion is going to be the energy of one of these fusion reactions. 67 00:06:44,500 --> 00:06:48,130 Times to the fusion cross-section shown here. 68 00:06:48,810 --> 00:06:53,260 I'm the density, the product of the density of our reactants, the deuterium and the tritium, 69 00:06:53,880 --> 00:06:56,530 the simplicity here, I'm assuming those two densities are going to be the same. 70 00:06:56,530 --> 00:07:00,280 So there's like the square, the density, and we first get our constraint here. 71 00:07:00,280 --> 00:07:05,620 Now, by staring at this, what you find is that if you look at this fusion cross-section for the nuclear physics, 72 00:07:05,860 --> 00:07:09,760 it has a temperature dependence and you find a peak in this thing at around 100 million degrees. 73 00:07:10,090 --> 00:07:15,610 So that's what sets our temperature to be as high as it is to maximise our fusion cross-section. 74 00:07:19,800 --> 00:07:23,640 What about this one, Graham business that comes from considering the stability of our plasma? 75 00:07:24,300 --> 00:07:29,490 So we know both from theory and from empirical observations, 76 00:07:29,700 --> 00:07:36,180 that there are limits on how much plasma you can stuff in your reactor before things start to go microscopically unstable. 77 00:07:36,690 --> 00:07:42,240 And in particular, if you try to put in densities much in excess of 10 to 20 particles per cubic metre, 78 00:07:42,540 --> 00:07:50,100 then we find that you have these macroscopic stability limits. At the same time, even if you say below that and everything's macroscopic, be stable, 79 00:07:50,400 --> 00:07:57,809 then hidden underneath what you're kind of looking at from the outside, you see little microscopic of instabilities that start to occur. 80 00:07:57,810 --> 00:08:02,730 You get little small scale turbulence. This mixes hot and cold regions. I'll talk about this a lot more throughout the talk. 81 00:08:03,450 --> 00:08:10,410 And the point is this limits the temperature gradients that you can sustain in your plasmas. 82 00:08:10,440 --> 00:08:14,519 And since you want to be hot in the middle, I did million degrees cold at the edge. 83 00:08:14,520 --> 00:08:18,180 So you don't melt walls. This limits roughly the size of the device. 84 00:08:18,750 --> 00:08:24,000 You're going to have to have to make this work. So it gives you a volume at something like one cubic metre. 85 00:08:24,180 --> 00:08:29,730 And so if you combine these two things, you find that you need about a gram of your fuel in the device at any one time. 86 00:08:31,220 --> 00:08:36,860 And so finally taking these all these numbers, plugging them back in up here and solving for my energy confinement time. 87 00:08:38,230 --> 00:08:45,150 Yet something which is on the order of a second. So this is really what we're aiming at in the fusion program. 88 00:08:49,120 --> 00:08:53,589 And so the first challenge I'm going to discuss is just how do we get the energy into the plasma at the outset? 89 00:08:53,590 --> 00:08:57,160 Because it seems like a pretty big problem, like heating something up to 100 million degrees. 90 00:08:57,880 --> 00:09:01,660 It turns out this is actually one of the best understood parts of the problem. 91 00:09:02,680 --> 00:09:10,960 And it turns out that the ways in which we heat it up are fairly standard ways that we see in other aspects of our lives. 92 00:09:11,440 --> 00:09:14,080 So the first thing that we tend to do is we use element heating. 93 00:09:14,680 --> 00:09:19,210 And that's just saying that we we work in the same way that a light bulb filament would work. 94 00:09:19,780 --> 00:09:25,000 And so you run current through this plasma, which is not a perfect conductor, has some resistivity. 95 00:09:25,270 --> 00:09:29,259 So when you run current through it, it heats up and it turns out that's pretty efficient, 96 00:09:29,260 --> 00:09:35,290 up to some tens of billions of degrees, maybe a third of the way. We need to get to our our fusion temperatures. 97 00:09:36,040 --> 00:09:37,869 And at some point, when the temperature gets very high, 98 00:09:37,870 --> 00:09:43,840 this resistivity of our plasma decreases and this becomes efficient way to find other ways to heat up plasma. 99 00:09:44,200 --> 00:09:45,780 And there are a variety of ways we do it. 100 00:09:45,790 --> 00:09:53,409 One of those common ways is to shoot in radio frequency waves and have these things resonate with the motion of our charge particles. 101 00:09:53,410 --> 00:09:56,440 And this accelerates our charged particles and heats them up. Okay. 102 00:09:56,620 --> 00:10:01,000 And so this is very effective, as is evidenced by scene such as this one, 103 00:10:01,480 --> 00:10:05,920 where you can see a bridge which is built such that its resonant frequency would resonate with the wind blowing past. 104 00:10:05,920 --> 00:10:13,120 Right. So this can be a very powerful phenomenon. It can get us the rest of the way up to 109 degrees if we can keep the energy in long enough. 105 00:10:15,060 --> 00:10:20,190 And so the basic idea of how are we going to keep that energy in with magnetic confinement, fusion is illustrated here. 106 00:10:20,400 --> 00:10:24,510 And so it's basically casting your mind back to your first year undergraduate physics. 107 00:10:24,930 --> 00:10:29,910 We simply take a charged particle. Shown here, I put it into a magnetic field which is coming out of this board. 108 00:10:30,420 --> 00:10:35,100 And you have some Lorentz force which is acting on that particle in a direction 109 00:10:35,100 --> 00:10:38,040 which is perpendicular to its motion and perpendicular to the magnetic field. 110 00:10:38,970 --> 00:10:44,220 So all it does is it take our charge particle and it makes it go in a circle about our magnetic field line. 111 00:10:44,910 --> 00:10:51,450 And now along the magnetic field is now this thing doesn't act on our particle in the direction along the field, 112 00:10:51,660 --> 00:10:53,790 so it's free to string along the field however it likes. 113 00:10:54,060 --> 00:11:01,650 And so in the end, you get these sort of sort of helical orbits of our charged particles that stream along these lines and gyrate about them. 114 00:11:02,620 --> 00:11:08,679 So that's the idea. And. The stronger your magnetic field is, the smaller this radius becomes. 115 00:11:08,680 --> 00:11:15,460 So if you put it really strong magnetic field, then into a pretty good approximation, the particles just stream along magnetic field lines. 116 00:11:17,020 --> 00:11:24,370 So the trick then is to find a way to take these magnetic field lines and somehow confine them to some surface or some volume. 117 00:11:25,360 --> 00:11:28,640 So that the particles can't leave. That's right. 118 00:11:29,530 --> 00:11:33,010 It turns out the only way to do that is to make them look like doughnuts. 119 00:11:35,090 --> 00:11:38,420 And so this is basically saying we're taking our magnetic field. 120 00:11:38,600 --> 00:11:42,560 It's some kind of vector field. We want to confine it to some surface. 121 00:11:42,800 --> 00:11:47,150 And this, Harry both tells us the only way to do that is with something topologically equivalent to a tourist. 122 00:11:47,630 --> 00:11:51,920 It's called the Harry Ball Theorem. Because of this diagram showing you on the left, 123 00:11:52,310 --> 00:11:58,610 the idea is if you try to take some ball or sphere with little hairs all over it and you try to comb those hairs, 124 00:11:58,610 --> 00:12:02,690 so they all lay in the surface, much like your vector field all needs to lie inside the surface. 125 00:12:02,960 --> 00:12:05,150 You find you could never make it lie flat everywhere. 126 00:12:05,660 --> 00:12:12,860 There was always be some cusps appearing somewhere which appear which correspond to zeros in your vector field, which is an acceptable way. 127 00:12:13,100 --> 00:12:16,880 This is why everything looks like these these doughnuts whenever you look at any fusion devices. 128 00:12:19,220 --> 00:12:25,730 So what I would like to do, if you'd indulge me, is look at the simplest possible doughnut and see if it works. 129 00:12:26,270 --> 00:12:28,880 And spoiler alert, it's not going to work. 130 00:12:30,200 --> 00:12:35,810 But in finding out that it's not going to work, we're going to see some of the physics we need to make it work. 131 00:12:36,740 --> 00:12:41,690 So here's a simple possible device we can kind of think of. We have just a current carrying wire. 132 00:12:42,660 --> 00:12:44,160 Parent carrying wire makes you feel, 133 00:12:44,160 --> 00:12:51,330 which gives you circles which encircle that wire and whose strength drops off like one over the distance from the wire. 134 00:12:52,510 --> 00:12:59,050 So what we're going to do is going to put a charge particle, give it like a proton into this magnetic field and see what happens. 135 00:13:00,170 --> 00:13:03,380 So naively, based on the picture I've just drawn for you earlier, 136 00:13:03,620 --> 00:13:07,650 we expect these things just filed around the seed line and go round and round and round. 137 00:13:08,360 --> 00:13:13,640 That's not going to happen. It's not going to happen because any time you have a curve magnetic field like this, 138 00:13:13,970 --> 00:13:17,630 it's going to have an in homogeneity, in the magnetic field strength. 139 00:13:17,960 --> 00:13:21,620 And that magnetic field string is going to stop these nice close orbits that we've been talking about. 140 00:13:22,370 --> 00:13:29,719 So that's illustrated here. So if I have my charged particle here and I zoom in on it and naively I expect it to 141 00:13:29,720 --> 00:13:33,470 generate around the field line and if I have a stronger field on one side than the other, 142 00:13:33,740 --> 00:13:38,690 then locally each gyro radius over here is going to be smaller than it is over here. 143 00:13:39,050 --> 00:13:47,210 And so your circle's not going to close. So instead it does something like this and it drifts vertically upwards. 144 00:13:47,480 --> 00:13:58,260 In this case. And so if you repeat the same process now for negatively charged particles for electrons, then they're going to drift downwards. 145 00:13:58,830 --> 00:14:02,040 So positive charges go up, negative charges go down. 146 00:14:02,570 --> 00:14:05,880 You get an electric field which is generated by this process. 147 00:14:06,150 --> 00:14:09,900 And so what we expect to happen presumably is something like this. 148 00:14:10,800 --> 00:14:14,100 So we have an electric field particles going to stream long electric field, right. 149 00:14:14,670 --> 00:14:18,270 Well, that's not right in the presence of a magnetic field. 150 00:14:19,080 --> 00:14:24,810 The Magnetised plasma gets something which looks kind of like the picture I showed you before in the case of, 151 00:14:25,260 --> 00:14:31,470 you know, what you need in the magnetic field. Namely, if I take any force and I put it in a direction perpendicular to my magnetic field, 152 00:14:31,740 --> 00:14:38,220 then you get these drifts and they drift for the same reason I argue, before particles are accelerated over this part of its orbit. 153 00:14:38,640 --> 00:14:45,600 And so it's local gyrating. It gets big. But at some point, the Lorentz force turns it around, its decelerated small dry radius. 154 00:14:45,600 --> 00:14:52,260 And so it it drifts the direction that's perpendicular, both to the force and to the magnetic field. 155 00:14:54,330 --> 00:14:57,900 So if we apply that now in our sort of simple doughnut device, 156 00:14:58,350 --> 00:15:03,990 we're going to see that you have drifts which are to the left in this case, maybe to the right out here, just radially outwards. 157 00:15:04,260 --> 00:15:08,250 So particle is a stream radially out of your device so it doesn't work. 158 00:15:10,270 --> 00:15:14,360 The solution. Solution, unfortunately, is to make life more complicated. 159 00:15:15,470 --> 00:15:19,700 And so instead of having these simple circles, you really do have to use the full set of stories. 160 00:15:20,150 --> 00:15:23,570 And so we can take a magnetic field, which before just went a long way around this doughnut. 161 00:15:23,570 --> 00:15:29,180 And now we're going to add a component which is the short way around the doughnut. And so my apologies, my lapse into jargon at some point. 162 00:15:29,480 --> 00:15:33,740 This is the toroidal direction, the long way around. And this is a little direction, the short way around. 163 00:15:35,250 --> 00:15:38,820 And so here it's illustrated how you generate such a set of fields. 164 00:15:39,270 --> 00:15:47,220 The idea is you would take some current carrying coils or magnets and put them encapsulating your plasma volume that will generate this, 165 00:15:47,520 --> 00:15:53,280 you know, the long way around. And what you can do is run some kind of currents up through the centre of your device. 166 00:15:53,280 --> 00:16:00,180 That changes in time. I don't want to use a current in your plasma and that generates these little magnetic fields around this way. 167 00:16:00,750 --> 00:16:02,160 And so I don't want to belabour the point, 168 00:16:02,460 --> 00:16:12,290 but this sort of common approach of generating this so called potent field is not a steady state way of generating your magnetic fields, right? 169 00:16:12,310 --> 00:16:16,530 Because to do this, you have to increase the current through this centre column in time. 170 00:16:16,950 --> 00:16:20,160 And at some point you can reach your current limit and you got to turn it off and start over again. 171 00:16:21,000 --> 00:16:25,080 So Georgia might talk a bit more about ways around this Hertog. 172 00:16:26,090 --> 00:16:29,360 Okay. So why does this help? I've said it's going to solve the problem if I put this twist. 173 00:16:29,390 --> 00:16:40,000 Now, let me try to convince you. So again, here now you can do this dot dash line as a line going vertically through the middle of this doughnut. 174 00:16:42,340 --> 00:16:49,140 And so if I took this circle and I rotate it around, that makes my tours. So again, let's put a charge particle here. 175 00:16:49,290 --> 00:16:51,960 It has an inhomogeneous magnetic field that's going to start drifting down. 176 00:16:53,160 --> 00:16:58,920 And now as it drifts down, it's also tied to a magnetic field which is moving around trying to make it stay on the circle. 177 00:17:00,260 --> 00:17:05,750 And so as it drifts down, it drifts off the steroidal surface. Now down here, it's drifting down, back on to the surface. 178 00:17:06,320 --> 00:17:10,280 And so if the device is symmetric with respect to this vertical line, 179 00:17:10,670 --> 00:17:14,810 then on average when the particle drifts, it's going to come exactly back to its starting location. 180 00:17:16,210 --> 00:17:21,760 So there's no net magnetic drift in this case. And so there's no radial transport of our particle. 181 00:17:22,750 --> 00:17:29,710 So what this means is this device, which has so-called axis symmetry called a tokamak, can confine individual charged particles. 182 00:17:33,530 --> 00:17:37,820 So this is the picture that I'm trying to sell you based on this single particle picture. 183 00:17:38,150 --> 00:17:46,760 Basically, if I take a bunch of these toroidal surfaces now and I put them inside one another like this, 184 00:17:47,180 --> 00:17:50,780 then we're going to find that energy in the particles attached to a given surface. 185 00:17:50,780 --> 00:17:53,720 Stay on that surface. So they're like metal insulators. 186 00:17:54,080 --> 00:18:00,440 And so you can imagine having a hot plasma in the middle, which is perversely blue here, and a cold plasma at the edge. 187 00:18:02,640 --> 00:18:10,200 Now, in reality, this is what happens in our plasma. So this is visible light which is emitted by the relatively cool plasma at the edge 188 00:18:10,200 --> 00:18:13,980 of an experiment just down the road at Culham Centre for Fusion Energy called Mast. 189 00:18:15,240 --> 00:18:21,090 And what you're seeing here, turbulent fluctuations of the surface of this toroidal surface in the plasma. 190 00:18:21,690 --> 00:18:27,329 And this is due to all these small scale instabilities that I mentioned and the resultant turbulence, 191 00:18:27,330 --> 00:18:30,989 which is going to makes hot and cold stuff in the plasma. And as I'll tell you a bit more about later, 192 00:18:30,990 --> 00:18:38,219 this is what limits are confinement time in the devices you just saw a minute ago that this sort of turbulence fluctuations largely went away here. 193 00:18:38,220 --> 00:18:46,950 And you get this nice, clean picture of our plasma now interspersed by these unfortunate violent outbursts of the plasma. 194 00:18:47,580 --> 00:18:51,720 And so what we can see something hopeful and something horrible in this picture, 195 00:18:52,080 --> 00:18:57,360 I hope will thing is that there's a way to take this turbulence which was mixing the hot and cold and to reduce it substantially. 196 00:18:57,360 --> 00:19:04,620 So you can barely see it any more in this image, but at the same time, it's replaced by these arguably much worse outbursts of the plasma. 197 00:19:05,160 --> 00:19:07,860 So these things on current devices are a nuisance. 198 00:19:08,130 --> 00:19:14,070 If they're bad enough in certain devices, they can damage some of the surrounding wall and components in a fusion reactor. 199 00:19:14,070 --> 00:19:17,370 If these things happen, there's so much energy that's going to be ejected out, they'll just melt the wall. 200 00:19:18,630 --> 00:19:23,850 So these are one of the things that community is very worried about, making sure that they can sort out. 201 00:19:23,910 --> 00:19:30,569 There's been a lot of progress on this, but most of the time I'm going to be talking about this turbulence problem in part because 202 00:19:30,570 --> 00:19:34,080 it does limit the confinement device and in part because that's what we do here at Oxford. 203 00:19:34,710 --> 00:19:38,370 So we're one of the world leading groups in trying to understand this turbulence and how we can reduce it. 204 00:19:39,180 --> 00:19:48,390 So the pretty picture I showed you before, these nice concentric, confined surfaces underneath lurking is this turbulence. 205 00:19:49,560 --> 00:19:53,520 So this is something which you can think of as triggering density fluctuations 206 00:19:53,940 --> 00:19:58,710 taken from a numerical simulation of one of these tokamaks out in California. 207 00:19:59,880 --> 00:20:06,480 And you can see some interesting features of this turbulence that hopefully by the end of the lecture today, you'll understand. 208 00:20:06,900 --> 00:20:10,910 So one of them that's quite striking is the fact that this treatment is highly isotropic. 209 00:20:11,350 --> 00:20:16,530 So if you follow one of these eddies, say this blue, and here you can see it's very long weighted in this direction. 210 00:20:16,530 --> 00:20:21,000 But by the time it comes over here, you get these little circles which are much smaller than the device. 211 00:20:21,780 --> 00:20:24,270 This is quite easy to understand. Without giving you any more physics, 212 00:20:24,810 --> 00:20:28,830 giving you it's in isotropic because you put a strong magnetic field in the plasma 213 00:20:29,160 --> 00:20:32,580 that introduces anisotropy because the particles are free to move along these lines, 214 00:20:32,580 --> 00:20:39,150 but not across these blue lines. Basically map out magnetic field lines in our device. 215 00:20:40,260 --> 00:20:47,070 What I haven't explained is why what actually sets the scale of these eddies in this sort of poetic cut? 216 00:20:47,100 --> 00:20:49,140 I'll talk a bit about that later. 217 00:20:49,590 --> 00:20:56,070 The other thing that's not quite clear yet is why is the turbulence seeming so much stronger out here on the outside and it is on the inside? 218 00:20:56,340 --> 00:20:59,410 That's another feature that will explain today. 219 00:21:02,230 --> 00:21:06,910 And so as soon as turbulence is mentioned, then perhaps your heart drops. 220 00:21:07,450 --> 00:21:11,380 I don't mind us sometimes late at night when I can't figure out a problem. 221 00:21:12,430 --> 00:21:18,910 And there's good reason because for a very long time now, people have been working on turbulence, using the neutral fluid context. 222 00:21:19,240 --> 00:21:26,590 And some very clever people are some examples of which are shown here have despaired about solving the problem. 223 00:21:26,620 --> 00:21:29,880 So here's a quote which is variously attributed to these gentlemen. 224 00:21:31,480 --> 00:21:34,150 And I guess what I can say is that it has been a big problem. 225 00:21:34,480 --> 00:21:39,340 This has been one of the reasons why Fusion has taken much longer than people thought originally. 226 00:21:39,340 --> 00:21:43,700 When people built these devices, they weren't counting on turbulence, mixing everything up. 227 00:21:43,720 --> 00:21:47,020 They were thinking collisions would just move particles out and slowly. 228 00:21:47,260 --> 00:21:52,690 And that's why you have these ideas of tabletop experiments or fusion might occur several decades ago now. 229 00:21:53,050 --> 00:21:57,610 And as it became more and more clear that turbulence was a problem, these devices got bigger and bigger. 230 00:21:58,930 --> 00:22:03,160 But what we are going to take today is say turbulence is complicated. 231 00:22:03,580 --> 00:22:05,680 Let's not try to approach the turbulence directly. 232 00:22:05,680 --> 00:22:09,250 Let's instead think about what drives that turbulence and see if there's a way we can shut off its drive. 233 00:22:09,940 --> 00:22:13,090 So linear physics is easier than nonlinear physics. So let's start there. 234 00:22:14,020 --> 00:22:22,149 So what is it that drives our turbulence? So asking the illustrated by this cartoon here you're looking at a cut now a piece of our tokamak. 235 00:22:22,150 --> 00:22:31,210 So that would be the Tokamak. We gyrated around in another board and we're going to focus on a little patch of plasma near the edge. 236 00:22:31,600 --> 00:22:35,049 And as I said, we want to seem to be hot in the middle for fusion to occur, cold at the edge. 237 00:22:35,050 --> 00:22:39,970 We don't melt their walls. So I expect the plasma on this little side of the patch, the hotter than it is over there. 238 00:22:41,440 --> 00:22:44,709 The only other piece of information we need is again, we have an inhomogeneous magnetic field, 239 00:22:44,710 --> 00:22:53,410 so we're going to have our ions drifting downwards in this diagram and the hotter ions have more random thermal motion. 240 00:22:53,800 --> 00:22:56,830 And so they're going to react down faster in the colder ions. 241 00:23:00,060 --> 00:23:04,710 So what happens if I take this nice picture where everything is perfectly well confined in return, but just a little bit. 242 00:23:06,080 --> 00:23:14,300 Then what I see is the following. So my hot particles, my hot irons approached this surface faster than they're leaving that surface. 243 00:23:14,840 --> 00:23:21,530 And so you can end up with a net excessive charge here. Up here, they leave this interface faster than the replenish. 244 00:23:21,920 --> 00:23:27,590 So you end up with a deficit of positive charges. And so you end up with this horrible thing we saw earlier that the problem, 245 00:23:27,590 --> 00:23:31,730 which is charge separation, positive and negative charge is alternating, which. 246 00:23:32,690 --> 00:23:39,530 Give rise to alternating electric fields. You have an electric field and a magnetic field, they give rise to drifts. 247 00:23:39,860 --> 00:23:44,960 And these drifts just so happened to reinforce the initial perturbation that we gain. 248 00:23:45,080 --> 00:23:51,170 So this is our mechanism for instability. We need a temperature gradient and we need magnetic field in 1980, and that's basically it. 249 00:23:52,190 --> 00:23:55,370 So if this were everything, then we'd be we would be in trouble. 250 00:23:57,330 --> 00:24:03,150 But if you repeat the analysis on another little patch of plasma on the inside of our device, then you find the opposite is true. 251 00:24:03,330 --> 00:24:08,850 Almost everything's the same. The only thing that's changed is that now the cold part of the plasma is on the left and the heart's on the right. 252 00:24:09,210 --> 00:24:16,830 All the other analysis is identical. And so what you find is that the drifts now actually work to stabilise the initial perturbation. 253 00:24:17,940 --> 00:24:20,960 So it's unstable on the outside, stable on the outside, inside. 254 00:24:20,970 --> 00:24:26,370 What's going to happen? Well, the competition between these two things gives rise to a critical temperature gradient. 255 00:24:26,700 --> 00:24:30,930 If you stay below that critical temperature gradient, then you have none of these micro instabilities. 256 00:24:31,320 --> 00:24:35,400 And if you go beyond that critical temp to gradient, then you have this instability, which is exciting. 257 00:24:36,260 --> 00:24:39,749 And so roughly speaking, you can see that here. 258 00:24:39,750 --> 00:24:45,750 If we took this horrible device, which is just circles, so purely toroidal field and if you looked at the plasma out here, 259 00:24:45,750 --> 00:24:50,490 it would just go unstable and it would grow and grow and grow. That nonlinear turbulence, that stuff happens. 260 00:24:51,120 --> 00:24:56,729 If you instead twist the magnetic field like we're proposing, then you take this instability, the amplitude start to grow. 261 00:24:56,730 --> 00:25:03,930 But at the same time, it's being swept along the field line to this stable region where these perturbations now decay. 262 00:25:04,920 --> 00:25:11,999 And so the analogy here is with this honey dipper, the idea being that if you take your honey deferred and leave it there stationary with honey 263 00:25:12,000 --> 00:25:16,920 on it and gravity pulls it off as gravity in this case is like the instability in your system. 264 00:25:17,610 --> 00:25:22,799 But if you rotate it fast enough compared to the rate at which gravity's pulling it off in the honey to stage on the dipper, 265 00:25:22,800 --> 00:25:27,050 because at some point gravity is doing a work for you and pulling the honey back onto the difference. 266 00:25:27,070 --> 00:25:31,290 It's the same thing you with the twisting magnetic fields. So what does this mean? 267 00:25:31,560 --> 00:25:40,710 It means that sort of the boring but reliable solution to the turbulence problem is to make a really big device. 268 00:25:41,730 --> 00:25:44,910 Right? Because if you make your temperature gradient sufficiently shallow, 269 00:25:45,510 --> 00:25:48,960 then as long as I make my device big enough, I'll get the high temperature I need in the core. 270 00:25:49,230 --> 00:25:53,400 And everything's fine, at least from the standpoint of turbulence. 271 00:25:53,670 --> 00:25:59,329 The other reason you don't want to do this, which I'll touch on later. But it's worth considering. 272 00:25:59,330 --> 00:26:04,040 Then what happens if we do inside these instabilities? Let's imagine I don't want an enormous device. 273 00:26:04,040 --> 00:26:09,740 I want to get a smaller device. And so how bad is my turbulence going to be if I cross the threshold? 274 00:26:10,900 --> 00:26:18,070 And to estimate this, what I'm gonna try to do is give you some argument for what the size of our energy should be in this turbulent system. 275 00:26:18,610 --> 00:26:21,639 And basically, the bigger the eddy, is it worse? 276 00:26:21,640 --> 00:26:25,690 The mixing is going to be right? You can make an eddy the size of your device. You're going to mix hot and cold stuff immediately. 277 00:26:25,900 --> 00:26:29,420 If you make tiny eddies, you can take a long time for the energy to diffuse out. 278 00:26:30,350 --> 00:26:37,520 So we're going to find that the Eddie Eddie's must be roughly the size of this gyro orbit particles around the lines. 279 00:26:37,880 --> 00:26:43,070 And you can think of that in a fairly crude way by saying that if the gyro radii were really, 280 00:26:43,070 --> 00:26:47,540 really small and effectively, they wouldn't see the magnetic field and homogeneity at all. 281 00:26:47,870 --> 00:26:52,160 There'd be no magnetic drifts and maybe be no instability wouldn't be a problem. 282 00:26:52,820 --> 00:26:58,880 And the other limit with it, a radius is very big compared to these perturbations that I've drawn here. 283 00:26:59,420 --> 00:27:03,649 Then the particle doesn't see all these little complicated physics of what's happening in the cold region. 284 00:27:03,650 --> 00:27:09,290 The hot region. It just averages over all this stuff. And so the instability goes away then as well. 285 00:27:09,620 --> 00:27:15,230 So the only perturbations are going to be a variety of instabilities or those which are the size of our gyrations. 286 00:27:16,880 --> 00:27:24,140 And so here's a pretty movie. Basically, I'm just showing you the simulation where you start out with the money instability. 287 00:27:24,140 --> 00:27:28,190 It's already gone away. Things have gone non-linear. Turbulent starts to fill out volume. 288 00:27:28,460 --> 00:27:31,970 And so you can see exactly all the stuff we've just been describing, turbulence, 289 00:27:31,970 --> 00:27:35,390 which is mostly unstable on the outside and the inside thing to stabilise. 290 00:27:35,720 --> 00:27:38,660 You also see something kind of interesting, which I'll come back to in a moment, 291 00:27:38,990 --> 00:27:44,629 which is you see all of these kind of differential flows appearing in the plasma and in regions. 292 00:27:44,630 --> 00:27:49,070 We have strong gradients, these flows, it turns out you can have the turbulence which largely goes away. 293 00:27:49,450 --> 00:27:52,460 Okay, so I'll come back to that in a few slides. 294 00:27:54,010 --> 00:27:59,950 But if we know that the any size of the gyro radius, how does that help us figure out how much confinement time we're going to get? 295 00:28:00,790 --> 00:28:04,660 Well, we can do that by coupling this to a random walk kind of estimate. 296 00:28:05,350 --> 00:28:11,379 So random, which are used in lots of different areas of physics, if you cast your mind back to undergraduate degree and your kinetic theory, 297 00:28:11,380 --> 00:28:17,740 you might realise the kinetic that these random what we use to estimate heat transport and neutral gases in there is collision. 298 00:28:17,740 --> 00:28:21,520 But you're moving things around here. It's a turbulent eddies which are moving things around. 299 00:28:22,240 --> 00:28:28,660 And so the idea is that a particle might start out on some eddy, this blue eddy here, and start moving along it in this black trajectory. 300 00:28:28,990 --> 00:28:33,910 At some point that eddy decays and is replaced by this green eddy. So the particle has taken one step. 301 00:28:34,390 --> 00:28:38,140 Now it takes another step along a different eddy and then other eddies. 302 00:28:38,140 --> 00:28:46,900 And this continues on and on and on. And over the course of this random work, what you can show is the time it takes to move some given distance. 303 00:28:46,900 --> 00:28:52,900 LS can be the time for step in the random walk and the ratio of how far you're looking to go. 304 00:28:54,240 --> 00:28:59,670 How big a step is it? And so if we put in all the quantities you just described to us, the system size, 305 00:28:59,670 --> 00:29:02,580 it's how long it's going to take for energy to take off in the middle to the edge. 306 00:29:03,330 --> 00:29:09,659 These the any size is our radius and the time for step is how long it takes a particle to move along. 307 00:29:09,660 --> 00:29:17,970 Our Eddy, you come out with this estimate the confinement time is about a second right at the edge of what we need to make fusion devices work. 308 00:29:18,750 --> 00:29:22,320 If this were way in excess of a second, then we wouldn't be here right now. 309 00:29:22,470 --> 00:29:25,470 Fusion would have been working much sooner than it currently is. 310 00:29:25,890 --> 00:29:30,360 Instead, we're right close to where we need to be going through here. 311 00:29:31,200 --> 00:29:39,900 So one of the big headlines that came out last year was this record fusion energy yield shot taken from the Jet Tokamak. 312 00:29:40,200 --> 00:29:47,760 Again, this is a column in the Centre for Fusion Energy just outside Oxford and it got 59 mega joules of energy over five or 6 seconds, 313 00:29:48,330 --> 00:29:53,520 which was sort of more than double the previous record also on Jet in a previous campaign. 314 00:29:54,870 --> 00:30:00,180 And if you look at the amount of energy that you get out of your plasma for this experiment. 315 00:30:01,530 --> 00:30:06,120 And compared to the amount of energy that actually hit the plasma, then what you find is, 316 00:30:06,120 --> 00:30:09,420 roughly speaking, that about half of the energy came out that you put in. 317 00:30:10,620 --> 00:30:16,590 So it's a net loss of energy. I say roughly because there are different ways to measure this, but it's roughly half what came up when. 318 00:30:17,400 --> 00:30:23,310 And so we need to go a bit further. I can confinement time to be at least a few times bigger than it currently is. 319 00:30:23,670 --> 00:30:28,350 And so the question is, how are we going to do that? And there are different approaches. 320 00:30:28,530 --> 00:30:32,580 The first one is the one I've already mentioned to you. Right. Let's just make our device really big. 321 00:30:33,450 --> 00:30:37,470 That way we can have small temperature gradients and still get the fusion images that we need. 322 00:30:38,970 --> 00:30:46,500 But this is not a uniform good idea, because, for instance, the bigger you make something, the more expensive it gets. 323 00:30:47,070 --> 00:30:53,010 Roughly, the cost tends to scale, like the volume of your plasma or the volume of your reactor. 324 00:30:53,010 --> 00:30:56,819 So bigger is going to be worse economically. Also, 325 00:30:56,820 --> 00:31:00,090 there's some technological issues with doing this because imagine you have a 326 00:31:00,090 --> 00:31:04,470 certain amount of energy in your plasma and now I make the plasma volume bigger. 327 00:31:05,250 --> 00:31:06,660 The energy goes up like the volume, 328 00:31:07,380 --> 00:31:14,250 but the walls that surround it through which all this energy is not to be taken out at some point only go up like the area, not like the volume. 329 00:31:15,090 --> 00:31:22,230 And so the heat hitting the wall per unit area goes up. And so at some point you have materials problems which are already on the edge of now, 330 00:31:22,800 --> 00:31:26,460 how are you going to take this heat out safely without damaging your device? 331 00:31:27,150 --> 00:31:30,840 But this is the approach roughly taken by etre. 332 00:31:31,350 --> 00:31:35,850 This is a schematic showing this ITER experiment which is being built currently in the south of France. 333 00:31:36,270 --> 00:31:41,740 And there's a person for comparison. So this is, of course, a very expensive device. 334 00:31:41,750 --> 00:31:46,790 It's ballooned in cost to something like €25 billion or something. 335 00:31:47,000 --> 00:31:51,170 So this might demonstrate that fusion is going to work in a scientific point of view, 336 00:31:51,170 --> 00:31:54,250 but it's not going to demonstrate that it's going to work economically. I give. 337 00:31:55,010 --> 00:32:00,320 It is the biggest experiment ever built coming online in a few years time. 338 00:32:00,800 --> 00:32:03,890 This is an old graphic, so it's over 80% complete now. 339 00:32:04,730 --> 00:32:11,630 But the idea behind this is that we hope to get out ten times the amount of energy that we actually put into the plasma. 340 00:32:12,650 --> 00:32:20,680 So this will be our scientific demonstration that you can make this work. Isn't the only approach to make things better. 341 00:32:21,970 --> 00:32:28,480 You can also take a technological sort of hack and try to make the magnetic field we're using stronger. 342 00:32:29,140 --> 00:32:33,490 As I told you, the stronger the magnetic field, the smaller the radius of these particles and gyration is, 343 00:32:33,760 --> 00:32:37,210 the smaller the eddies become, the better you can find guns. That's the idea. 344 00:32:37,660 --> 00:32:40,270 And so hope we can get away with a smaller device by doing this. 345 00:32:40,770 --> 00:32:44,890 And so this is the approach that's being taken by a number of private companies these days. 346 00:32:45,100 --> 00:32:48,790 Commonwealth Fusion Systems in Cambridge, Massachusetts. 347 00:32:49,180 --> 00:32:55,240 Tokamak Energy just outside Oxford. The idea is they're going to use high temperature superconducting magnets. 348 00:32:55,780 --> 00:33:01,900 You're still creating this technology when you get ten times as much magnetic field in these devices than we're currently using. 349 00:33:02,620 --> 00:33:06,610 So that's the big selling point. It is still in development, this technology. 350 00:33:06,970 --> 00:33:11,830 And you have a problem, which is that if you put such huge magnetic fields over such a small area, 351 00:33:12,160 --> 00:33:15,100 the stresses on all of your material components become enormous. 352 00:33:15,700 --> 00:33:19,750 So you have another sort of technological problem, and how do you actually keep everything from tearing itself apart? 353 00:33:23,170 --> 00:33:30,430 And finally, the approach which I guess all of the things this approach may be is to reduce the aspect ratio of your device. 354 00:33:31,390 --> 00:33:38,470 So we started out most we've been showing you look what these sort of tokamak which look like this, they look more like doughnuts or bicycle tires. 355 00:33:39,010 --> 00:33:44,680 But one idea is to use what's called a spherical tokamak or spherical Taurus, which is more like a cold apple. 356 00:33:45,760 --> 00:33:50,020 And the benefit behind this is that, again, remember that the magnetic field strings, 357 00:33:50,170 --> 00:33:55,320 the toroidal magnetic field string drops off like the distance from the centre of this apple. 358 00:33:55,990 --> 00:34:02,260 So if you bring your plasma in really close, then you get the magnetic field for free it simply by doing that. 359 00:34:03,610 --> 00:34:07,659 That's one benefit. The second benefit is that the rate of filtering is going to drop off really 360 00:34:07,660 --> 00:34:11,680 rapidly as you move across this volume because it goes like one over the distance. 361 00:34:11,950 --> 00:34:14,470 And so as you get very close to it, it drops off rapidly. 362 00:34:14,800 --> 00:34:21,880 So and these devices, the field is mostly toroidal on the inside, but it has quite a significant political component on the outside. 363 00:34:23,110 --> 00:34:30,040 You might ask, why is that good? Well, if you remember, the plasma in here is stable and the plasma out here is unstable. 364 00:34:30,680 --> 00:34:36,970 And what this means is that plasma spends a long time where things are stable and very little time where it's unstable. 365 00:34:37,720 --> 00:34:42,400 So this is going to improve our confinement and our micro stability in these. 366 00:34:43,810 --> 00:34:48,070 There are issues with this as well. There's no free lunch. One of the big issues is what do we get? 367 00:34:48,070 --> 00:34:52,090 If you have such a small space here in the middle of your device, 368 00:34:52,780 --> 00:35:01,150 how are you actually going to put like shielding to stop neutrons from kind of destroying sort of your central solenoid in this case? 369 00:35:02,590 --> 00:35:06,550 You also have the same problem with heat loads the inverse to the big reactor. 370 00:35:06,940 --> 00:35:11,169 So here, Matt, you say you take a different approach. You say I want a gigawatt coming out of this thing. 371 00:35:11,170 --> 00:35:17,960 I want a gigawatt power plant. And so that sets how much energy is coming out of your device. 372 00:35:18,330 --> 00:35:23,540 If I now take my walls and I make them really, really, really small, which is great from the point of view, 373 00:35:24,020 --> 00:35:26,390 you still have a huge amount of energy coming out of a very small area. 374 00:35:27,340 --> 00:35:33,640 So there are also some technological challenges, this type of approach, and this is the approach largely being championed in the UK. 375 00:35:33,670 --> 00:35:37,930 So based that video I showed you earlier is one of the UK fusion experiments here. 376 00:35:37,930 --> 00:35:44,830 It's a vehicle for this step shown here, which is being funded by the UK Government. 377 00:35:45,250 --> 00:35:53,870 Is a reactor like design using this vehicle tourists concept and also Tokamak Energy is pursuing these simple tours, right. 378 00:35:53,890 --> 00:35:56,920 So the UK is kind of championing this approach. 379 00:35:58,290 --> 00:36:05,040 So I've given you some different ideas for how we're going to do this. What I'd like to say now in the very limited amount of time I have left, 380 00:36:05,370 --> 00:36:10,709 is that some of the things we're trying to work on as theorists is understanding ways in which we 381 00:36:10,710 --> 00:36:15,500 can improve the confinement time independent of any of these approaches that I've laid out for you. 382 00:36:15,930 --> 00:36:22,980 If we can suppress the turbulence, then that gives us a lot more leeway in the design of our fusion reactors. 383 00:36:23,250 --> 00:36:31,110 And so here I'm going to give you one possible way that you can try to suppress turbulence in these devices showing this cartoon. 384 00:36:31,350 --> 00:36:34,320 So, again, I want you to imagine a magnetic field coming out of the board here. 385 00:36:34,620 --> 00:36:39,420 And I have my little particle which is gyrating in that magnetic field shown here by this black circle. 386 00:36:39,930 --> 00:36:45,540 And I have some turbulent eddies here, which, if you stay in one of these eddies, is going to take you across the plasma and makes hot and cold. 387 00:36:46,890 --> 00:36:52,830 So as I mentioned, these particles gyrate with a radius roughly the size of one of these eddies. 388 00:36:53,340 --> 00:36:57,060 So any given particle is going to stay within its eddy and makes hot and cold. 389 00:36:58,130 --> 00:37:04,310 Now what I'm going to do is I'm going to say let's take a flow which is going up on the right and down on the left. 390 00:37:04,340 --> 00:37:10,970 So here's my shear flow. What does that do? It takes my eddies and it stretches and tilts them in a way that I've shown here. 391 00:37:11,330 --> 00:37:15,860 So the now a particle which is gyrating around this field line actually samples multiple these eddies. 392 00:37:16,520 --> 00:37:22,250 So the first eddy, it might start to be taking heart outwards and then it starts to come inward and then outwards. 393 00:37:22,520 --> 00:37:28,080 And so again, as you average over many, many of these eddies, it effectively reduces the efficacy of these eddies to and. 394 00:37:29,390 --> 00:37:34,500 So this is one way that people are trying to suppress turbulence. 395 00:37:35,840 --> 00:37:42,469 Now I know I said I'm mostly focussed on turbulence and that's what I've done, but I don't want to completely neglect other advances in the field. 396 00:37:42,470 --> 00:37:46,310 So I'm going to quickly show a couple of slides here and some other exciting developments. 397 00:37:46,850 --> 00:37:48,649 So this is one development that hit the news. 398 00:37:48,650 --> 00:37:57,260 Also, I came into this this year, last year, now using machine learning to help us shape our plasma and stop macroscopic instabilities. 399 00:37:57,770 --> 00:38:02,149 And so what you're seeing here are this this outer sort of shape. 400 00:38:02,150 --> 00:38:05,660 Here is the vessel wall for an experiment in Switzerland TV. 401 00:38:06,440 --> 00:38:10,890 And this is the plasma that you're seeing inside that, doing some set of experiments. 402 00:38:11,420 --> 00:38:15,650 And what they've done is they've tried very hard to achieve certain plasma shapes. 403 00:38:16,020 --> 00:38:22,010 Turned out by shaping the plasma, you can change the properties of both the turbulence and the macroscopic stability. 404 00:38:22,730 --> 00:38:28,790 But this is a difficult challenge. They come up with these shapes because if you have no plasma, then sure, 405 00:38:28,790 --> 00:38:32,900 I can design some magnetic fields which you can to map out whatever shape I'm trying to get. 406 00:38:33,110 --> 00:38:37,610 But as soon as you put the plasma in, it generates its own magnetic fields which interact with these ones, 407 00:38:37,610 --> 00:38:41,630 which change the plasma, which change these. And so it's a complicated feedback system. 408 00:38:42,230 --> 00:38:49,040 And so what they've done is they've used machine learning in collaboration with DeepMind to have some target shapes they wanted, 409 00:38:49,040 --> 00:38:51,410 which are given by these blue circles. 410 00:38:51,920 --> 00:38:59,960 And they've used real time feedback, control this machine, learning to give it the shape they wanted over time in the device. 411 00:39:00,200 --> 00:39:07,700 So AI is not just good for making dark tiles, it's actually starting to do something useful for us. 412 00:39:09,000 --> 00:39:11,670 I don't want to say much about this. George is going to talk about celebrities in a minute. 413 00:39:12,060 --> 00:39:16,320 But I do want to say that one of the big problems that we're still going to have overcome at some point in the future is how to make a device, 414 00:39:16,320 --> 00:39:20,310 a steady state and not inherently pulsed, as I've discussed before. 415 00:39:20,580 --> 00:39:24,360 And sort of the leading contender for doing this, I would say, are stellar ideas, 416 00:39:24,360 --> 00:39:29,250 which are ways of making these magnetic surfaces that don't have currents running through the plasma. 417 00:39:30,100 --> 00:39:37,370 Okay. So this is my last slide. Basically it's showing some measure of progress, confusion over the years. 418 00:39:38,210 --> 00:39:41,410 So on this axis, it's a measure performance is this thing called the triple product. 419 00:39:41,410 --> 00:39:45,890 That's basically the pressure times, the confinement time versus year. 420 00:39:46,160 --> 00:39:49,940 And we're comparing progress in fusion with that in other areas. 421 00:39:50,060 --> 00:39:52,910 So you have Moore's Law shown here in red. 422 00:39:53,420 --> 00:40:02,460 The energy of particle accelerator shown in green and Z fusion is actually very respectable on this plot blot because, 423 00:40:02,510 --> 00:40:06,470 you know, we might say we started out very low, but anyway, we've we've moved quite far. 424 00:40:06,800 --> 00:40:13,160 And I mean, the obvious elephant in the room here at this ends at 2000, but that was the last time we pushed things forward. 425 00:40:13,760 --> 00:40:19,340 Higher performance, really? And that's just because neither has been on the horizon forever. 426 00:40:20,510 --> 00:40:25,460 Right. And so it should put us up here. 427 00:40:27,260 --> 00:40:33,320 It's going to be a pretty big leap. And so, obviously, you know, we're all waiting anxiously for this to happen. 428 00:40:33,500 --> 00:40:39,980 But one of the things that has really changed in recent years is that this is not the only thing on the horizon anymore. 429 00:40:40,700 --> 00:40:46,939 Right. We now have a range of private fusion companies who, whatever you think about them, 430 00:40:46,940 --> 00:40:53,720 are promising to give you results somewhere between these two on this line in a faster timescale. 431 00:40:54,230 --> 00:40:58,850 And so the nice thing about this is, you know, putting all of your eggs in one basket. 432 00:40:59,910 --> 00:41:04,350 We actually have a lot of different ideas coming out at the same time, and I'm going to be testing them in real time. 433 00:41:04,980 --> 00:41:08,700 There's a lot of excitement in the program that now we're actually building all these different things, 434 00:41:08,700 --> 00:41:14,910 all these different approaches all at once, which you really need to do, I think, to test out, you know, what's going to happen next. 435 00:41:15,930 --> 00:41:19,130 So I'm going to leave you with that and if you have any questions. 436 00:41:19,230 --> 00:41:20,880 Yeah, thanks.