WEBVTT 1 00:00:02.290 --> 00:00:03.260 Mark Kushner: I'd be helpful. 2 00:00:04.440 --> 00:00:05.370 Mark Kushner: Wow. 3 00:00:06.240 --> 00:00:18.979 Mark Kushner: Well, welcome to, this week's Mitzi seminar, and just to begin with a reminder, we are entering into choosing seminar speakers for next academic year. 4 00:00:19.020 --> 00:00:29.600 Mark Kushner: So, you still have a week or so to make suggestions for speakers for next year. Go to the MIPSI homepage, and there's a link to enter in your suggestions. 5 00:00:31.020 --> 00:00:37.239 Mark Kushner: It's my pleasure to introduce Dr. Philip Bonifiglo as today's NFC seminar speaker. 6 00:00:37.370 --> 00:00:42.230 Mark Kushner: Phil is staff research scientist at the Princeton Plaza Physics Laboratory. 7 00:00:42.360 --> 00:00:51.409 Mark Kushner: He received a Bachelor of Science from the University of Michigan. We have an alumnus. I hope you're keeping up your annual giving. 8 00:00:51.840 --> 00:01:00.050 Mark Kushner: When he was introduced to plasmas by performing high-energy density physics experiments, and this was part of… 9 00:01:00.500 --> 00:01:02.620 Mark Kushner: of Carolyn's group. Yes. Yes. 10 00:01:03.740 --> 00:01:22.220 Mark Kushner: I then attended the University of Wisconsin-Madison, where he transitioned from HED physics to magnetic confined fusion. His thesis work was at the Wisconsin Plaza Physics Lab, investigating fast transport and field… reverse field pinches. 11 00:01:22.220 --> 00:01:23.799 Mark Kushner: With Jay Anderson. 12 00:01:24.090 --> 00:01:39.070 Mark Kushner: After his PhD, Phil joined the Prince and Plaza Physicists Lab, first as a postdoctoral researcher, where he specialized in the confinement and transport of energetic particles, combining numerical simulations with experiments. 13 00:01:39.540 --> 00:01:50.010 Mark Kushner: Since then, his research has spanned almost every configuration of magnetic-compliant fusion, from accelerators to tokabaks. 14 00:01:50.210 --> 00:02:01.129 Mark Kushner: He participated in the recent DT campaign on JET, the Joint European Taurus at the Kohlheim Center for Fusion Energy in the UK. 15 00:02:01.160 --> 00:02:19.289 Mark Kushner: And he has upcoming experiments on the Megaamp Perispherical Tokamak upgrade, that's a mass cube at Kohlhem, and when the NXTX upgrade comes online, as we will hear early next year, and that's located at Princeton. 16 00:02:19.690 --> 00:02:29.929 Mark Kushner: The title of Phil's talk today is Magnetic Confinement Fusion, the Path to the Spherical Tokamak, the NSTXU Upgrade. 17 00:02:30.760 --> 00:02:39.100 Mark Kushner: And to thank you for making the trek to Ann Arbor, we present you with the MIPSI Monk. Thank you. 18 00:02:42.270 --> 00:02:43.140 Mark Kushner: Thank you. 19 00:02:43.250 --> 00:02:44.600 Mark Kushner: Thank you. Thank you, Phil. 20 00:02:46.080 --> 00:02:50.410 Mark Kushner: Alright, thank you. To… 21 00:02:51.360 --> 00:02:58.599 Mark Kushner: To start, I was going to introduce myself, but you actually already kind of got a short introduction myself. I'm… 22 00:02:58.760 --> 00:02:59.600 Mark Kushner: Yep. 23 00:03:00.510 --> 00:03:13.070 Mark Kushner: Probably better, hopefully better? Yes. So yeah, I did my undergraduate here, I'm also born and raised in Michigan. I was actually a UROP student, which I think that program still exists, so I highly encourage it to all the undergraduates. 24 00:03:13.070 --> 00:03:23.709 Mark Kushner: I then started magnetic confinement Fusion at Wisconsin, as you just heard, and then I transitioned to Princeton and PPPL, where I've been ever since. Still in magnetic confinement Fusion, and yeah, I've… 25 00:03:23.750 --> 00:03:31.349 Mark Kushner: I think I'm one of the few people who've actually worked on almost every type of magnetic confinement fusion device, tokamak accelerator. We're gonna go through them all, so don't worry about it. 26 00:03:31.690 --> 00:03:45.159 Mark Kushner: If you don't know what PPPL is, it's the Princeton Plasma Physics Laboratory. It's a national lab, one of 17. It is actually managed and overseen by Princeton University, so it's a member of both the DOE and Princeton University. 27 00:03:45.160 --> 00:03:51.970 Mark Kushner: It's existed since the 1950s, originally a classified project of… called Project Matterhorn, where we 28 00:03:51.970 --> 00:03:56.400 Mark Kushner: invented the Stellarator, but since it's grown into a massive, or… 29 00:03:56.400 --> 00:04:02.880 Mark Kushner: Relatively small national lab that's 700 employees, and tons of publications, tons of… tons of projects, a lot of funding. 30 00:04:03.280 --> 00:04:14.559 Mark Kushner: So, what are we gonna learn today? We got a lot to cover, but I'm going to start out slow, and we're gonna build to… in, complexity. So, I'm going to talk about why do we need Fusion, what it is. 31 00:04:14.560 --> 00:04:22.020 Mark Kushner: how do we… or why do we need confinement? And then, the bulk of my talk is, how do we confine a plasma? Obviously, we're going to be doing it through magnetic fields. 32 00:04:22.019 --> 00:04:39.589 Mark Kushner: And that's going to lead us to a bunch of different magnetic confinement schemes this year. We're going to talk about the pros and cons of each device, and that's going to lead us to the spherical tokamak and NSTXU, which is going to be the device that we're going to build and operate at Princeton. It's going to be one of the few devices existing in the United States, actually. 33 00:04:39.600 --> 00:04:45.440 Mark Kushner: And so they're going to essentially end where are we now, and what are our biggest obstacles and problems to overcome as a whole, as a field. 34 00:04:46.280 --> 00:04:55.670 Mark Kushner: So, why do we need fusion? If you're not aware, fusion power is… it's safe, it's abundant, it's energy-dense, clean, sustainable, all positive words. 35 00:04:55.700 --> 00:05:07.920 Mark Kushner: You can't have runaway reactions, unlike a fission plant. There's only a small amount of fuel. If the particles cool, your plasma cools, and the reactions just stop, and everything just kind of subtly terminates and ends. 36 00:05:07.960 --> 00:05:24.619 Mark Kushner: We also have abundant fuel supply. As I'm gonna mention, you're gonna primarily use isotopes to deuterium and tritium. Deuterium we can naturally breed from seawater. We got a lot of that hanging around on Earth. And tritium you can breed from lithium in the Earth's crust, of which we readily mine already for many of our electronics. 37 00:05:24.620 --> 00:05:45.120 Mark Kushner: It's very high energy density, it's the most efficient process for mass, and there's very minimal radioactive waste compared to fission and other energy sources. So, at most, you're going to have trace amounts of tritium, tritium is slightly radioactive, and you're going to have neutron-activated material. So, there will be some radioactive waste, but nothing too bad. And of course, there's going to be no CO2 production. 38 00:05:45.850 --> 00:06:04.579 Mark Kushner: So, the way this functions is very, very similar to a fission power plant. Fusion power plant, you're gonna have your machine that's gonna produce fusion. That's gonna produce neutrons, you're gonna use those neutrons to heat water. Run, your hot water through a heat exchanger to produce steam, use steam to push into the turbine, and to put it on the grid. So… 39 00:06:04.580 --> 00:06:22.790 Mark Kushner: Exact same principles as a fission power plant, except this time we're using fusion to produce the neutrons. And so, again, you're going to surround this in a water blanket, and you're also going to surround it in lithium or a fly blanket, and that's what you're going to use to make tritium production. So, one of the byproducts of your neutrons is actually producing tritium, which is one of your fuel sources that you need. 40 00:06:23.330 --> 00:06:25.229 Mark Kushner: So, that's it. 41 00:06:25.490 --> 00:06:38.679 Mark Kushner: What is more fusion in more detail? Well, it's a pretty simple reaction. You're essentially exploiting the fact that we're converting, binding energy, mass to energy. This equation cut off, but I hope everybody here knows it, delta equals MC squared. 42 00:06:38.690 --> 00:06:54.319 Mark Kushner: And as I'll talk in a moment, this is by far the most common fusion interaction or reaction that we're going to talk about and discuss. And so that's combining deuterium and tritium to produce an energetic helium-4 alpha particle, as well as a 14 MeV neutron. 43 00:06:54.500 --> 00:06:56.010 Mark Kushner: And so, as I mentioned. 44 00:06:56.030 --> 00:07:10.380 Mark Kushner: Neutrons are gonna be one of your byproducts. You're going to use the neutrons both for power production by heating your water, as well as for breeding tritium by bombarding it into lithium. And then, as well as these energetic helium ions, they're going to be around 3.5 MeV. 45 00:07:10.380 --> 00:07:17.660 Mark Kushner: As we'll discuss, your bulk plasma here, that comes composed of deuterium and tritium, they're on order of 10 keV, so these are… 46 00:07:17.660 --> 00:07:35.769 Mark Kushner: orders and orders of magnitude higher energy, and so what you do is you self… you can find these alpha particles, and they will then self-heat the plasma via collisions down to the thermal population. So you use the alpha particles, essentially, to keep the plasma temperature up, to keep the reactions going, essentially continuing to stoke the fire, the nuclear fires, if you will. 47 00:07:36.150 --> 00:07:53.159 Mark Kushner: So, fusion is more energetically advantageous to fission. Most of you have probably seen this plot before, but this is the famous plot of the average binding energy per nucleon as a function of the atomic number in your nucleus, and so it peaks at iron56, 48 00:07:53.160 --> 00:08:08.220 Mark Kushner: And on the left-hand side, we have fission that goes all the way up to iron56, and on the right-hand side, we have fission going downward. And so, fission, you're taking heavy things, going to smaller. Fusion, taking light things, and going bigger. And then obviously, the big jump here 49 00:08:08.220 --> 00:08:22.880 Mark Kushner: is noticeable on the fusion end, and so this is exactly what we're trying to do. We're taking isotopes of deuterium and tritium, and we're jumping them up to helium-4, and you can see there's this huge jump in the relative energy, and so that's what makes fusion the most efficient per mass unit. 50 00:08:24.050 --> 00:08:42.330 Mark Kushner: And so, again, I've mentioned this on and off, why are we talking about DT? Why do we keep using DT or isotopes of deuterium and tritium? Well, simply put, it's the easiest. So this is just simply the cross-section of interaction for fusion, as a function of various, ions, and you can see that deuterium 51 00:08:42.380 --> 00:08:53.670 Mark Kushner: deuterium tritium, here in blue, has the highest peak, so it has the highest strong, the strongest, cross-section, as compared to, like, de-helium-3 or DD, or PB11, or what have you. 52 00:08:53.820 --> 00:09:02.239 Mark Kushner: However, we're not going to operate there. We actually operate somewhere around here, because we end up peaking around 10 to 20 kV due to radiative and transport power losses. 53 00:09:02.390 --> 00:09:09.039 Mark Kushner: And so, what the name of the game is, is we're eventually going to maintain a high temperature and dense plasma to induce fusion reactions. 54 00:09:09.270 --> 00:09:18.480 Mark Kushner: Some asides, there are some groups that are investigating non-DT concepts, so while we do focus on DDT, excuse me. 55 00:09:18.480 --> 00:09:34.069 Mark Kushner: Other groups are investigating D3 helium and PEB11. The advantages of those are that they're anneutronic, so you don't have to deal with any pesky neutrons. You can do direct energy conversion with the alphas produced. However, it's much harder. The cross-sections are smaller, so you need higher temperatures, so… 56 00:09:34.070 --> 00:09:36.559 Mark Kushner: It becomes a lot more complex. 57 00:09:36.560 --> 00:09:53.929 Mark Kushner: I'll also note that even though we want to do DT, DT experiments are actually exceedingly rare. We had recent experiments in JET, which is a tokamak in England, a couple years ago, but then prior to that, the last DT experiments in magnetic confinement fusion were in the mid-1990s, which is a big gap. 58 00:09:53.930 --> 00:09:58.339 Mark Kushner: So, they're not common. Most research plasma nowadays are doing DD, DD, 59 00:09:58.340 --> 00:10:04.589 Mark Kushner: DD Fusion. So, almost all of what you see in presentations is DD. Everything I'll show you here will be DD, actually. 60 00:10:05.430 --> 00:10:06.340 Mark Kushner: So… 61 00:10:06.850 --> 00:10:21.820 Mark Kushner: How do we achieve fusion? What do we want to do? Well, this is essentially based on what we call the Lawson criteria. And so, again, what we want to do is essentially create a plasma of DT ions to overcome the Coulomb repulsion, because they're going to be ions of the same charge, they're going to naturally repel each other from Coulomb repulsion. 62 00:10:21.820 --> 00:10:29.250 Mark Kushner: And so this plot here shows a plot of the temperature of your plasma, corresponding to these three parameters, which I'll break down in a moment. 63 00:10:29.310 --> 00:10:42.600 Mark Kushner: If you're above these lines, that means you're energy positive. You're getting more energy out than in, and then, if you're below that line, it means you're energy negative. So what you want to do is you want to be above these lines. So essentially what that means, you want a high temperature and high… 64 00:10:42.600 --> 00:10:53.220 Mark Kushner: properties of these. So, we can break them down. First, density. You want to be at high density. This naturally makes sense, because if you're trying to overcome Coulomb repulsion, well, just simply pack more particles together. 65 00:10:53.880 --> 00:11:02.109 Mark Kushner: The next is high temperature. Again, it's kind of a natural thing. If you want to overcome coolant repulsion, we'll just give them more energy so they can naturally overcome that barrier. 66 00:11:02.250 --> 00:11:20.569 Mark Kushner: Of note, we have already hit the temperatures necessary to achieve fusion, and we did this way back in the 1990s at TFTR in Princeton. We hit 250 million Celsius, which got us right here on the curve, right where we need to be. And so that leads us to this last parameter, which is tau E, which is the so-called confinement time. 67 00:11:20.690 --> 00:11:35.670 Mark Kushner: And so you might be thinking, well, why do we need confinement? Why does confinement matter in any of this? And again, you can think of it in simple physics terms of overcoming the Coulomb repulsion, high density, pack them together, high temperature, give them enough energy, and high confinement time essentially means, oh, we need enough 68 00:11:35.880 --> 00:11:44.970 Mark Kushner: time of interaction to occur. But why do we need that? Why do we need confinement? Because naively, we could come up with this simple idea. 69 00:11:45.010 --> 00:11:46.459 Mark Kushner: Why don't we take… 70 00:11:46.460 --> 00:12:11.320 Mark Kushner: some high-energy beams with some high density fuel and slam things together. As scientists, we're very good at making high energy beams. You could look at the Large Hadron Collider, for example. They… they accelerate things to stupidly high energies, so why can't we go to high energies or high densities? So, imagine we have some frozen DT fuel here at high density, and we just slam some beams into it. Why does that not work? Or why don't we take two beams and 71 00:12:11.320 --> 00:12:12.959 Mark Kushner: And slammed them together. 72 00:12:13.380 --> 00:12:38.340 Mark Kushner: Well, simply put, you have to consider other interactions, mainly collisional scattering. If you just take, consider collisional scattering, this is the plot of the cross sections. These dashed lines are your scattering. These bottom lines here are your, your fusion cross-sections of interaction. And this is a logarithmic scale, so these… the fact… the probability that you will collisional scatter instead of having a fusion event is orders and orders of magnitude 73 00:12:38.340 --> 00:12:53.209 Mark Kushner: higher. So you must have sustained confinement. That's essentially saying you need to keep all of your particles together, around long enough such that you're gonna have many, many scattering events before fusion even occurs. So that's why you need confinement. You have to overcome this scattering effect. 74 00:12:54.110 --> 00:12:55.020 Mark Kushner: So… 75 00:12:55.430 --> 00:12:59.229 Mark Kushner: How do we do that? How do we confine a plasma? This is going to be the bulk of the talk. 76 00:12:59.750 --> 00:13:02.209 Mark Kushner: Gravity. Well, that's too slow. 77 00:13:02.820 --> 00:13:17.700 Mark Kushner: What about ICF? That's… that's one method, but I'm gonna say it's not the subject of this, this talk. So, they use radiative compression, you're gonna use lasers to, irradiate this gold cylinder here, which is called a Hallram. 78 00:13:17.750 --> 00:13:35.809 Mark Kushner: And then that hall room is going to translate into a plasma, which is going to impinge your fuel with X-rays, and you're radiatively gonna compress your fuel. So that is a method, but obviously it's not the method. Obviously, we're going to be talking about magnetic confinement fusion. You can kind of think of this as a magnetic bottle, if you will. So that's what we're going to talk about today. 79 00:13:36.310 --> 00:13:45.409 Mark Kushner: So, we know we need to heat a gas to high temperature to make a plasma, and that we're going to confine it with a magnetic field. 80 00:13:45.940 --> 00:14:05.789 Mark Kushner: However, we know that plasmas are this soupy mixture of negatively charged electrons and positively charged ions that are not only susceptible to electromagnetic fields, but they can also generate their own electromagnetic fields, right? A moving current is going to create a magnetic field, and if you have a plasma, it can have a current in it, which can generate a magnetic field. 81 00:14:05.820 --> 00:14:12.679 Mark Kushner: And so this brings up the question, or the notion, of your magnetic field that will confine your plasma. 82 00:14:12.820 --> 00:14:23.409 Mark Kushner: Is it going to be due through external magnets, or is it going to be due to internal currents in the plasma, which will naturally create its own magnetic field? Or is it going to be a mixture of the two? 83 00:14:23.410 --> 00:14:34.730 Mark Kushner: And so this naturally kind of leads to this spectrum here, and this ultimately leads to all of the different designs and different machines, towards fusion energy. It's all about your choice. 84 00:14:34.730 --> 00:14:50.080 Mark Kushner: of your magnetic topology and how you're creating your magnetic field. On one end, you could say you have self-organized plasmas. These are akin to, like, pinches, and that means these plasmas kind of naturally relax into self-evolved states, and they produce kind of their own magnetic fields. 85 00:14:50.260 --> 00:15:07.179 Mark Kushner: they can't entirely produce their own magnetic fields, you must always have an external magnetic field. If you only had a plasma with just its self-contained magnetic fields, you need infinite energy, actually, so it's not possible. You must have some external force. But these plasmas are largely, largely self-organized here. 86 00:15:07.240 --> 00:15:18.489 Mark Kushner: And then the far end, you could say, well, imagine I don't have any currents in my plasma, I just want to use external magnets. That's fine, too. Those are going to be akin to stellarators, which I'll talk about later, tell you how those function. 87 00:15:18.490 --> 00:15:28.369 Mark Kushner: And then Tokamax, which are the other famous, fusion concept, which we'll break down later as well, those are actually somewhat in the middle. They have external magnets, but they also have internal currents to the plasma. 88 00:15:28.740 --> 00:15:33.909 Mark Kushner: So, let's kind of go through these and kind of move ourselves along this spectrum. 89 00:15:34.040 --> 00:15:45.419 Mark Kushner: Starting kind of from more easy designs to more sophisticated and more complex. To start, let's talk about a Z-pinch. It's relatively easy, but it is unstable. 90 00:15:45.420 --> 00:15:57.439 Mark Kushner: It's actually a very simple design. You can imagine you have a capacitor, or a capacitor bank, and you have a differential voltage, so you charge up a capacitor, and you discharge it, so that will drive an axial current. 91 00:15:57.440 --> 00:16:08.850 Mark Kushner: Well, this axial current that you drive is then going to induce an azimuthal magnetic field. Just a simple right-hand rule. We're going to do a lot of right-hand rule today. So, we're going to create a azimuthal magnetic field. 92 00:16:08.850 --> 00:16:27.309 Mark Kushner: But that magnetic field is going to create a J cross B force. That J cross B force is going to be inward, and again, another right-hand rule, and that's going to compress the plasma radially inward. So, again, this is a very simple design. In fact, there's not even any magnets. You're just simply driving a current by discharging a capacitor, which makes it very cheap. 93 00:16:27.360 --> 00:16:49.529 Mark Kushner: However, there are some cons that I'm not going to go into. We don't have enough time to talk about magnetohydrodynamics, or MHD, but it is MHD unstable, as well as there's some engineering and scaling issues when you want to make this bigger. There are active solutions, such that you can solve the MHD instability with some shear flow stabilization, but that's all work in progress. 94 00:16:50.480 --> 00:17:03.180 Mark Kushner: Another idea is a magnetic mirror. Again, it's a very… another simple design, nothing too complex. And so you can imagine that you kind of have these, circular, your current coils. 95 00:17:03.220 --> 00:17:17.069 Mark Kushner: And you use them to drive an axial magnetic field going left and right. And so what you do is on your… on the right here and on the left here, you make the magnetic field here stronger, so you're essentially choking the magnetic field down. 96 00:17:17.220 --> 00:17:26.749 Mark Kushner: And so what you're gonna have… what's gonna happen is particles are gonna go back and forth, back and forth along this axial magnetic field until they hit this, this region of high magnetic field. 97 00:17:27.069 --> 00:17:37.629 Mark Kushner: Classically, this is a simple problem of just a ball in a valley, right? So particles will slash back and forth within the valley, as long as they have sufficient energy, which is kind of… 98 00:17:37.900 --> 00:17:47.820 Mark Kushner: the tipping point. So this is one of the sticking points of the mirror, is that they are inherently lossy. So you get this thing called the loss cone, so this is the velocity, 99 00:17:48.120 --> 00:17:55.849 Mark Kushner: Velocity with respect to the magnetic field, so parallel would be along the axis in the previous plot, and perpendicular would be perpendicular to it. 100 00:17:55.850 --> 00:18:12.489 Mark Kushner: And if a particle has sufficient parallel energy, if it has enough energy to get over the hill, well, then it's just gonna get over the hill and it's going to escape, so you're just going to have an inherent loss for particles of sufficient energy, which is bad. You want to confine your particles, you don't want to just send them out of the machine. 101 00:18:12.490 --> 00:18:19.089 Mark Kushner: So, again, it's a very simple design, but it suffers from this inherent losses. There's other aspects of MHD stability. 102 00:18:19.090 --> 00:18:29.689 Mark Kushner: And traditionally, around its original concept, in order to overcome some of the stability and losses, you needed to make it very long, like on the order of 1 to 2 kilometers. 103 00:18:29.760 --> 00:18:38.649 Mark Kushner: that's not outside the realm of engineering. You consider, like, things like LIGO is on the order of a kilometer or two or something like that. But still, you know, smaller is better and cheaper. 104 00:18:38.650 --> 00:19:01.360 Mark Kushner: There are active solutions. Obviously, one of the simple solutions. Just make the magnetic field here stronger, and that narrows the choke point, and you bring this loss cone down. So that's actually something that a group is actually studying now. There's also kinetic stabilization of the MHD stability, and you can actually create good field curvature in the N cells. The N cells are regions past here that also helps with the MHD stability, but we're not going to go into that. 105 00:19:02.680 --> 00:19:09.360 Mark Kushner: We also have the first, the field reverse configuration. This actually exploits a self-organization phenomena. 106 00:19:09.450 --> 00:19:20.040 Mark Kushner: And so what you do is you have, again, your axial coils here. They're these gray bars that go circular around in and out of the page. And so what you do is you set another B field axially, going in this direction. 107 00:19:20.040 --> 00:19:25.290 Mark Kushner: And then what you do is you set that field, then you ice in the field, and then you quickly reverse that field. 108 00:19:25.290 --> 00:19:50.239 Mark Kushner: And when you quickly reverse that field, you actually have… magnetic reconnection will occur. So this is when you actually pinch and break your magnetic field lines, and you create these closed magnetic field contours and a little plasma current within the plasma. And so, that's one way to do it, but you actually can create field reverse plasmas or field reverse configurations in many ways. You can do it by collisional merging of plasmoids or beam injection. 109 00:19:50.360 --> 00:19:58.029 Mark Kushner: There's many methods, but they always produce this kind of reversal of the field, and self-organization into this, this state. 110 00:19:58.220 --> 00:20:04.729 Mark Kushner: So, a pro is that most of the magnetic field is actually self-created or self-organized via this magnetic reconnection process. 111 00:20:04.730 --> 00:20:23.269 Mark Kushner: It has a very weak magnetic field relative to pressure, which means it's high beta. We'll talk about beta later on. The cons, again, always kind of sticking around, is MHD stability, and you need active control for doing this. And so, you can get that with shaping coils and for beams injection. 112 00:20:23.420 --> 00:20:30.679 Mark Kushner: But yes, a lot, a lot of, a lot of, active work going into this, by, by private fusion companies and national labs. 113 00:20:31.210 --> 00:20:42.020 Mark Kushner: So, in all of those previous concepts, they all kind of relied on this axial magnetic field that was kind of, you know, linear 1D across in the Z direction, say. Well, the simple sense is, well. 114 00:20:42.030 --> 00:20:58.029 Mark Kushner: why don't we just take a magnetic field and wrap it in around itself in a donut? So take your coils here and just wrap them into a circle and create kind of like a circular solenoid, right? That way, you don't have an end to your magnetic field. And so, that's the simple intuition. 115 00:20:58.300 --> 00:21:11.360 Mark Kushner: Well, if we do that, we know that forces perpendicular to a magnetic field are going to create velocity drifts. In particular, we have the curvature drift, which is just due to the curvature, the fact that you're bending it into a circle. You can think of this as, like, the centripetal force. 116 00:21:11.360 --> 00:21:20.260 Mark Kushner: As well as the grad B drift here, which is due to a gradient in the magnetic field, and this is due to the 1 over R component that you get from your circular coils. 117 00:21:20.660 --> 00:21:35.969 Mark Kushner: And so when you do that, you can find that you have these drifts in your velocities of your particle, your guiding sphere velocities. And so for a magnetic field going this way, your radius of curvature and gravity are this way, you're going to find that you're going to get vertical drifts up and down. So your particles will move up and down. 118 00:21:35.970 --> 00:21:45.120 Mark Kushner: Okay, when… another side note, very quickly, just because it's important to my work in energetic particles, you'll notice that these are proportional to the energy of the particle, that's what E is here. 119 00:21:45.120 --> 00:21:55.170 Mark Kushner: So, the… as I mentioned earlier, the DT alphas that you measure are 3.5 MeV. They're orders and orders of magnitude higher than the bulk plasma. So, just by looking at this. 120 00:21:55.170 --> 00:22:12.389 Mark Kushner: it tells you that the drifts for your energetic particles, your alpha particles, are going to be substantially different than your thermal particles in your plasma. And so that necessarily dictates that your energetic particles are going to view your magnetic topology completely different, and they must be handled separately. So that's just an aside for energetic particles. 121 00:22:13.350 --> 00:22:17.610 Mark Kushner: Again, you have your drifts, they're gonna go up and down. Well, if you have up and down, Whoop. 122 00:22:18.310 --> 00:22:20.440 Mark Kushner: There's also a charge here, Q. 123 00:22:20.600 --> 00:22:24.740 Mark Kushner: That means you're gonna get charge separation. Ions go up, electrons go down. 124 00:22:24.770 --> 00:22:36.119 Mark Kushner: If that occurs, though, then you're inducing electric field. If you're inducing an electric field, that's going to put a force on your particles. That means you're getting E cross B force outward, and that E cross B force outward is going to be everywhere around the donut. 125 00:22:36.120 --> 00:22:57.980 Mark Kushner: So that inherently says you're going to be pushing particles outward, which is bad. Again, that just means your confinement is not working. And so how do we solve this? Very simplistically, actually. We solve this by adding a helical twist. So instead of having this axial magnetic field that goes around your donut, you're also going to add another field in the minor radius of your donut here, so… 126 00:22:57.980 --> 00:23:10.059 Mark Kushner: We use the mathematical terms torus, or, you know, toroidal and ploidal. Toroidal, it's a long way around the donut. Ploidal is the short way around the donut. So you want a toroidal magnetic field, as well as a poloidal magnetic field. 127 00:23:10.570 --> 00:23:27.529 Mark Kushner: And so essentially what happens, it means that as your particles move and go around, they're going to experience different parts of the field, as they go up and down, and so those drifts are naturally going to cancel out to zero. And so then there's a… as the drifts cancel to zero, they're going to be perfectly conf… well, perfectly well confined in the plasma. 128 00:23:28.540 --> 00:23:43.080 Mark Kushner: And so this brings up, actually, the notion of the safety factor, or the Q profile, which I want to bring in. So the safety factor is this, and it's the ratio of the number of times a magnetic field line travels toroidally per poloidal transit around your donut. 129 00:23:43.600 --> 00:23:57.140 Mark Kushner: And so, I want to touch on this. Again, we don't have a lot of time to delve into MHD and other complex plasma physics, but the Q profile safety factor is profoundly important for magnetic confinement fusion. If you want to sound 130 00:23:57.140 --> 00:24:04.690 Mark Kushner: professional or fancy at a conference, just ask someone what the Q profile is, or have them show you the Q profile, because this… this defines everything. 131 00:24:04.690 --> 00:24:21.619 Mark Kushner: So naturally, it's this equation here. So what you can see is you very quickly, you have your minor and your major radius, as well as your toroidal and politoidal fields. So what does that mean? It means your Q profile inherently defines your magnetic topology and equilibrium, which is everything in magnetic confinement fusion. That's how everything is defined. 132 00:24:21.620 --> 00:24:27.850 Mark Kushner: Of note, if we're talking about stellarators, they typically use the IOTA profile, which goes, like, 1 over Q. 133 00:24:28.210 --> 00:24:46.659 Mark Kushner: You might be wondering why it's called a safety factor. That's largely historical. Effectively, what will happen is, as Q starts to become less than 1, a bunch of stability… instabilities will occur, and your plasma, will become strongly unstable, so it became a safety issue, way back in the day. 134 00:24:46.860 --> 00:25:11.759 Mark Kushner: And so you can see some examples here. For a tokamak, this is what the profile looks like as a function of miter radius. It peaks somewhere around 1 and then monotonically increases. Well, it doesn't have to monotonically increase, it could have, reverse shear, but increases as you get to the edge. And then accelerators can vice versa. And then all of your reverse field pinches actually have your poloidal and your toroidal components, largely of equal magnitude, so it means, your Q is much less than 135 00:25:11.760 --> 00:25:15.229 Mark Kushner: So RFPs and stuff are, as I mentioned earlier, strongly unstable. 136 00:25:15.230 --> 00:25:37.949 Mark Kushner: But this is a very important, property, this, this Q profile, the safety factor, and it defines a lot of your physics that you see in your plasma in regards to if Q is less than 1, or if Q equals M over N, which is rational surfaces, or if there's shear, or where the edge value is, this all determines various instabilities and stability properties of your plasma. It comes up all the time in MHD, so… 137 00:25:37.950 --> 00:25:39.170 Mark Kushner: I just want to point that out 138 00:25:40.420 --> 00:25:58.650 Mark Kushner: Again, so we know we need this helical twist, we need it to create the poloidal field in addition to the toroidal field, so the question is, how do we do this? And adding this helical twist essentially leads us to our two most common, or two most popular methods for magnetic confinement fusion, the tokamak and the stellarator. 139 00:25:59.790 --> 00:26:08.459 Mark Kushner: So, we'll start with the Stellarator. So, simply put, the Stellarator simply adds a twist via non-planar coils, so… 140 00:26:09.180 --> 00:26:28.500 Mark Kushner: Very simply, you're not doing anything fancy with the plasma or anything, you're literally just going to shape the magnetic coils into this crazy twisting structure as you go around the donut. And so here's an example of a CAD rendering of Wendelstein 7X, which is a stellarator in Germany, and you can see it's quite complex. You can see the vacuum vessel here, and the coils are these orange circular shapes. 141 00:26:28.500 --> 00:26:44.929 Mark Kushner: And they're kind of these oblong, very strange shapes. So it's actually quite a feat of engineering. And then you can see here is the corresponding cross-section of your plasma at different angles or different times as you go around the donut. You can see they're completely different shapes. So this is inherently a 3D problem. 142 00:26:45.270 --> 00:27:00.919 Mark Kushner: So, this is good, because you don't have any currents in the plasma. Currents are big sources of instabilities, as we'll get to. So there's no current drive. It's inherently steady state. As long as you run your magnets, as long as you run your coils, you're just going to keep going. So this means you have better MHD stability. 143 00:27:01.160 --> 00:27:17.200 Mark Kushner: However, as I obvious, as I mentioned as well, it's inherently a 3D problem, and so us physicists or engineers, we typically love things that are symmetric. We love symmetry. We are now inherently breaking our symmetry, and so the, 144 00:27:17.560 --> 00:27:32.170 Mark Kushner: what that means is that in order to find a magnetic field, it has to be solved numerically. There is no analytic solution for a 3D topology of a stellarator. Also, what this means is you have traditionally poor particle confinement, because as I mentioned in, 145 00:27:32.170 --> 00:27:39.080 Mark Kushner: If you can think back to the magnetic mirrors, magnetic mirrors, you get these bouncing of particles because they hit high field, high field, and they go back and forth. 146 00:27:39.080 --> 00:28:03.679 Mark Kushner: But when you do that in a stellarator, you can now get bouncing in this toroidal direction, because you can have a high point here, toroidal, and a high point here, so you can get bouncing of particles this way. And when you get trapped particles in these sub-regions, they'll actually completely drift out of the machine, because they won't experience the full rotational transform, they won't experience the full safety factor Q profile, so their drifts don't average out, and they just drift out of the machine. So it has a very traditionally poor particle 147 00:28:03.680 --> 00:28:10.400 Mark Kushner: refinement. As well as, obviously, as I mentioned, I mean, just look at this, engineering complexity up the wazoo. 148 00:28:11.530 --> 00:28:24.330 Mark Kushner: Of note, though, solving for the B field numerically and the poor particle confinement is kind of a solved problem, through computational optimization. These are probably solved, so we can actually computationally solve 149 00:28:24.340 --> 00:28:43.049 Mark Kushner: not only for the magnetic equilibrium, but for the magnetic equilibrium and the design of the coils that make perfectly fine particle confinement on par with tokamax. So it's actually kind of a solved problem. We still have yet to build many of the optimized accelerators, but numerically, solved issue. 150 00:28:43.960 --> 00:29:02.140 Mark Kushner: What about a tokamak? How does a tokamak add this twist to the helical field? Well, again, we still have our solenoidal coils here. These are actually going to drive… they're called your toroidal field coils, because they drive the toroidal component, or field. So, simply put, you know, drive your current, and that's going to create your toroidal field around the plasma. 151 00:29:02.570 --> 00:29:21.360 Mark Kushner: Next, essentially, the plasma and the tokamak is going to act like a transformer, to drive an electric field. So you're going to have this central solenoid here, you can see the little circles here of the solenoid. That's going to act as your primary coil, in your transformer, and then your secondary coil in your transformer is going to be your plasma. 152 00:29:21.390 --> 00:29:38.320 Mark Kushner: So what do you do is you pulse your… you pulse your central solenoid, which will then induce an electric field, which is then going to induce a plasma current within your… your plasma. Again, a lot of right-hand rule, and, basic physics. 153 00:29:38.590 --> 00:30:00.960 Mark Kushner: And so when you induce this electric field, it induces this plasma current, and of course, again, more right-hand rule, if you're driving a plasma current in this toroidal direction, you're going to get a poloidal magnetic field going this direction. So you have your toroidal field driven by your coils, and then your poloidal field here is driven by your plasma current, in your plasma that is driven through the center stack here, your central solenoid. 154 00:30:00.960 --> 00:30:04.539 Mark Kushner: So that's the fundamental operating principles of a tokamak. 155 00:30:05.260 --> 00:30:06.270 Mark Kushner: So… 156 00:30:06.350 --> 00:30:31.310 Mark Kushner: What this leads to is actually better particle confinement. Again, this is actually 2D symmetric. As you go around the donut, it's inherently symmetric, unlike the Stellarator. It has a simple planar coil design, so it's much more easier to engineer. It has a simpler power exhaust, because again, unlike a stellarator, you just have a simple power exhaust at the bottom, as we'll talk about later. And there are analytical solutions to the equilibrium, so since the equilibrium is 2D in nature, just in 157 00:30:31.310 --> 00:30:38.070 Mark Kushner: in the poloidal plane. You can anecdotally solve it. This is the so-called Gradgefranov equation, which hopefully many of you know. If you don't. 158 00:30:38.070 --> 00:30:45.680 Mark Kushner: You need to know it. The cons are, is that you have to drive this magnetic… this megaamp level of plasma current. 159 00:30:45.680 --> 00:30:50.660 Mark Kushner: And so that means, it's gonna be a pulse device, because you have to drive this plasma current. 160 00:30:50.660 --> 00:31:06.030 Mark Kushner: Also, that plasma current is now a source for many instabilities. In fact, because you can think the plasma current's going to have a profile, and so you always need a driving source for instabilities, and so the gradient in your plasma current profile is going to actually naturally act as that driving source for plasma instabilities. 161 00:31:06.030 --> 00:31:17.619 Mark Kushner: Additionally, because of these instabilities in the plasma current, a tokamak is also prone to disruptions, which is a rapid loss of confinement. We'll touch on that a bit later. Disruptions are bad. That essentially means 162 00:31:18.070 --> 00:31:27.420 Mark Kushner: gain… you… like, the plasma is lost, in a sense. It's rapidly cooled, or you have a runaway current, something like that, and the reactions die. So, bad… that's bad. 163 00:31:27.680 --> 00:31:41.019 Mark Kushner: Now, what about a spherical tokamak? So, I mentioned spherical tokamak at the beginning of this talk. This is what we're currently building at Princeton and PPVLU. Well, simply put, a spherical tokamak is just a shrunk and compact tokamak. That's really all it is. 164 00:31:41.020 --> 00:31:51.699 Mark Kushner: It's the same fundamentals as a tokamak, but instead of oper… you know, looking more like a donut, you just shrink it, and it's more like a cored apple. So you'd essentially squish everything together. 165 00:31:51.700 --> 00:31:53.360 Mark Kushner: And so, 166 00:31:53.360 --> 00:32:12.969 Mark Kushner: In terms of your aspect ratio, which is your big radius of your little radius, it's at a lower aspect ratio. Kappa is your elongation, which is this length divided by this length, so it's at a higher elongation. Again, you're just squishing it. And then it's at traditionally, a higher beta. Beta is this parameter here, which is your plasma pressure relative to your magnetic pressure. 167 00:32:14.200 --> 00:32:33.129 Mark Kushner: And so, the pros is, well, it's smaller. Smaller is good in terms of engineering and cost. That means it's cheaper to build. And it's high beta, which means there's more fusion power for magnetic field. Again, so this beta is your particle pressure relative to your magnetic pressure. I kind of think of this as your bang for your buck. How much… 168 00:32:33.130 --> 00:32:46.930 Mark Kushner: how much particle pressure are you getting out per your magnetic field? Naturally, you want that to be quite high in terms of fusion. Additionally, it has favorable curvature for MHD stability and confinement properties as well. 169 00:32:47.240 --> 00:33:12.129 Mark Kushner: Some cons, however, is that as you squish it, obviously, this narrow central region where you have your central solenoid is naturally gonna be… it's gonna be much smaller, so there's not a lot of room to build your central solenoid, which means that the inductive current you're driving in your… in your plasma, just like, you know, your transformer, is gonna be smaller, so it's a lot harder to inductively drive your current. Additionally, because it's smaller, you're going to have higher heat loads on everything. 170 00:33:12.130 --> 00:33:15.130 Mark Kushner: Because the surface area, is naturally less. 171 00:33:15.530 --> 00:33:23.429 Mark Kushner: As well as, if you have too high to beta, I know it said it's a good thing, it's best bang for your buck, if beta gets too high, you can have more instability, so you don't want to go too high. 172 00:33:24.430 --> 00:33:25.350 Mark Kushner: So… 173 00:33:25.500 --> 00:33:43.350 Mark Kushner: We are building, or I guess we're saying we're upgrading, NSCX and NSCXU upgrade, the National Spherical Tokamak Experiment Upgrade, are going to resume near the end of the year in Princeton. So this is a view of the device here. You can see it's right here in the center. These red things here are your corresponding toroidal field coils. 174 00:33:43.350 --> 00:33:57.319 Mark Kushner: It has neutral beams, which you use to heat the plasma, as well as a high harmonic fast wave. These are just radio waves, you can use to heat the plasma. It looks something like this in your CAD drawing. Here's a person for relevance. This is probably, like, 2 to 3 stories tall, something like that. 175 00:33:57.320 --> 00:34:20.929 Mark Kushner: This is what it looks like on the inside. You can see it fits about, you know, a person, person and a half in there. These are all the tiles that you need to shield your device. Of course, it's going to be under vacuum when you're operating. You can see a port here for your neutral beam injection, and then this right here is an array of antennas to launch the RF waves to heat your plasma. And then, well, here's just a pretty picture of an old NSTXU plasma. 176 00:34:20.929 --> 00:34:23.020 Mark Kushner: You can see the curvature here along the… 177 00:34:23.030 --> 00:34:26.600 Mark Kushner: The center stack here, and then toroidally, it goes around like this, so… 178 00:34:26.659 --> 00:34:30.620 Mark Kushner: Nice, nice purplish glow that you'll get from DD plasmas. 179 00:34:32.070 --> 00:34:51.210 Mark Kushner: So, how are we actually upgrading it? Well, we're actually replacing the entire center stack, the entire central solenoid, and so what we're going to do is we're actually going to up… we're gonna double our magnetic field from half a Tesla up to one Tesla, we're gonna double our plasma current, and we're gonna double our pulse length from… or, excuse me, five times our pulse length from 1 to 5 seconds. 180 00:34:52.179 --> 00:35:11.419 Mark Kushner: We're also going to substantially increase our heating power. We're going to go from about 5 megawatts, I think somewhere about 10 to 12 megawatts of neutral beam injected heating power, as well as current drives. So your neutral beams can not only heat the plasma, but they can also drive current in the plasma, because you're essentially injecting particles 181 00:35:11.420 --> 00:35:18.970 Mark Kushner: Along a rate trajectory that is tangential to Your plasma currents. 182 00:35:20.310 --> 00:35:33.930 Mark Kushner: And so, essentially, we're going to be exploring a lot of unexplored regimes, that were previously unexplored. Again, what we're trying to achieve is high NT taui, high density, temperature, and confinement. We should get up to a factor of 10 higher than we previously got. 183 00:35:34.000 --> 00:35:43.610 Mark Kushner: Consequently, though, we're going to get to 4 times the heat flux onto our plasma-facing component services, so we have some ideas to mitigate that, which I'll talk about in a moment. 184 00:35:43.650 --> 00:35:58.119 Mark Kushner: And of course, if you go to higher temperature, this means you're going to get to lower collisionality, which is going to have more plasma effects. And one of the things we hope to do is, because we have such strong neutral beams, we hope to do fully non-inductive current drive from the beams, so… 185 00:35:58.120 --> 00:36:17.500 Mark Kushner: effectively saying, oh, we don't need the central solenoid to inductively drive our current. What if we just use the neutral beams to shoot in and drive our plasma current? This has never been demonstrated before, so we hope to do that, and it's going to be essential for steady-state operations in a one-day spherical tokamak reactor. 186 00:36:17.500 --> 00:36:24.629 Mark Kushner: So, what are some of the biggest obstacles and problems, and how are we addressing that in Spherical Tokamax and NSTXU? 187 00:36:24.630 --> 00:36:40.379 Mark Kushner: One of the natural questions is, how does your confinement time vary with aspect ratio, right? So you have a… you have your standard tokamak, and you have your spherical tokamak, right? One is a donut, one is more like a cord apple, and so, like, what is the natural effect of just changing its shape, of squishing the apple? 188 00:36:40.720 --> 00:36:48.150 Mark Kushner: So, this relation here, this is your energy confinement time. Your confinement time as a function of various, engineering parameters. 189 00:36:48.160 --> 00:37:04.039 Mark Kushner: This A here is your aspect ratio, major radius, elongation, density, input heating power, toroidal field, plasma current. This was found purely empirically, which is shown here. So, this is your experimentally measured confinement time as a function of 190 00:37:04.240 --> 00:37:19.829 Mark Kushner: Compared to this relation. And so what you do is you simply put a power series on every single one of these, variables, and you can get… you find that you get this nice linear relation right on the line. So this was found empirically, and all of these are various tokamaks and spherical tokamak devices. 191 00:37:20.280 --> 00:37:22.220 Mark Kushner: And as you can see. 192 00:37:22.330 --> 00:37:40.920 Mark Kushner: this goes like, well, like, roughly 1 over square root of A, so as A gets smaller, your confinement time gets bigger, naively. And so the question is, can we isolate this effect on aspect ratio, on, confinement time? And how can we truly compare 193 00:37:40.920 --> 00:37:54.719 Mark Kushner: a low aspect ratio plasma, like NSTXU, to a conventional aspect ratio plasma, right? It might be simplistic to say, oh, let's do an experiment on this one, an experiment on this one, and just compare. 194 00:37:55.020 --> 00:38:06.319 Mark Kushner: But you have different densities, different temperatures, so it's not a straightforward one-to-one comparison. And so, one of the things I'm actually probing around now is actually self-similarity studies. 195 00:38:06.320 --> 00:38:25.610 Mark Kushner: Where if we can actually find subspaces of similar dimensionless variables, in particular collisionality, rhoStar, beta Q&A, various dimension variables, can we find subspace, similar subspaces in these dimensionless quantities that we can better compare the plasmas that can ultimately reveal this aspect ratio? As well as 196 00:38:25.950 --> 00:38:34.780 Mark Kushner: our new experiments, but… so this is a previously unexplored question about this relation about aspect ratio, but it's something we hope to answer, in our upcoming experiments. 197 00:38:35.010 --> 00:38:50.059 Mark Kushner: Additionally, I'll say tokamaks are prone to very small-scale microinstabilities. This is known as turbulence. You can think of turbulence just as you do on an airplane or any other, you know, fluid-like property. So you have turbulence, which produces eddy-like structures. 198 00:38:50.060 --> 00:39:06.549 Mark Kushner: And these eddies can lead to an outward diffusion of particles, both in particle and energy. And so if you get all these eddies tallied together, that's going to lead to an outward transport of your particles in your heat flow, and that's going to be bad, because again, we want to keep everything nice and hot and in the plasma. 199 00:39:06.720 --> 00:39:14.470 Mark Kushner: And so we know that we can have flows within the plasma, so if you add flow shear, you can shear these eddies and then break them apart. 200 00:39:14.960 --> 00:39:24.080 Mark Kushner: And when you do that, you naturally degrade the turbulence, and you make your heating, your particle and your heat confinement much better. 201 00:39:24.340 --> 00:39:35.470 Mark Kushner: And spherical tokamaks and conventional tokamaks have different regimes for this turbulence. There's all sorts of different modes and turbulent regimes due to their curvature, shear, and their beta values. 202 00:39:36.660 --> 00:39:48.200 Mark Kushner: And so one of the big questions is, how does the confinement time vary in spherical tokamax at low collisionality? So how… how are all of these turbulent properties affected at low collisionality? 203 00:39:48.200 --> 00:39:49.150 Mark Kushner: for both 204 00:39:49.150 --> 00:40:13.539 Mark Kushner: Well, in general, but more importantly, as a function of aspect ratio as well, as a function of your low aspect ratio spherical tokamak, and your higher aspect ratio scaling traditional, standard tokamak. And so we're actually going to do this in NCXU. If you look at here, this is a function of your collisionality. As we go to reduce collisionality, we kind of go upward in this trend, and there's essentially two routes for the theory to go. 205 00:40:13.790 --> 00:40:38.720 Mark Kushner: Do we go on this upward-trending scale for low A scaling, which is… which would be good. This implies that at lower collisionality, your confinement increases. This would be a big win for spherical tokamaks. Or does it kind of curve and flatten off as your conventional aspect ratio standard tokamak? And so NSCXU, again, as I mentioned, we're going to be at a higher temperature, we're going to be at a higher total of field, higher heating power, which is going to drive us to lower collisionality. So we're actually going to be able to fill in some of these dots, and hopefully we can 206 00:40:38.720 --> 00:40:41.959 Mark Kushner: We can better answer this question of what is the confinement time 207 00:40:42.270 --> 00:40:51.909 Mark Kushner: at low collagenality, and this could be a nice bullet point for or against spherical tokamax, but we'll have to do the experiments and see. So will this scaling hold or not? 208 00:40:53.020 --> 00:40:59.300 Mark Kushner: The next is we also have wall divert issues. Again, as I mentioned, we're gonna have very high heat loads, and so… 209 00:40:59.450 --> 00:41:24.359 Mark Kushner: your plasma is constructed like this, you have some outward closed flux surface where all of your magnetic field is, and then eventually you're going to have an open flux surface here, which is called your last closed flux surface, your separatrix, and it's going to go down to an X point. So you're going to have plasma exhaust, you know, plasma will naturally exhaust from your plasma, you can't fully confine 100% of it, just like, you know, a car exhaust, and it's gonna go down this last closed flux surface, down to this X point, and into this region here called the diverter. 210 00:41:24.360 --> 00:41:28.569 Mark Kushner: And so this diverter here is naturally going to experience very high heat loads. 211 00:41:28.570 --> 00:41:38.379 Mark Kushner: As well as the wall, the surrounded wall region, but especially the diverter. This could be due from elms, which are edge-localized modes. These are kind of bursty modes that kind of pulse outward heat and particle flux. 212 00:41:38.390 --> 00:42:01.870 Mark Kushner: But you need to be cognizant of your wall material. So traditionally, walls are made out of something low Z, carbon or beryllium, but more and more, we're transitioning to tungsten, because it has very good, properties for handling high heat flux. However, tungsten has a Z of 74, and again, this got cut off, unfortunately, again, but if you know, your power of your Bremser-lung radiation goes as Z squared. 213 00:42:01.870 --> 00:42:18.999 Mark Kushner: So this is going to go, like, 74 squares. If you get tungsten that spatters black into your plasma, it will radiatively cool the plasma very quickly, which is going to lead to a disruption. Your plasma's going to cool, and you're gonna get loss of confinement. So we need to better understand these material properties that we construct our wall and diverter off. 214 00:42:19.000 --> 00:42:25.210 Mark Kushner: our wall and our diverter of, especially if we make it out of tungsten, because radiated velocities will be terrible. 215 00:42:26.050 --> 00:42:48.080 Mark Kushner: So, in NSCXU, we're going to use liquid lithium to do this. We did it previously on LTX Beta, which is a smaller spherical tokamak at Princeton, and so essentially what you do is you coat things in liquid lithium, and so this naturally reduces heat, load to the walls and diverters, it also reduces impurities, that's the backspattering of your wall materials and your plasma, and it's been shown to improve confinement time and also reduce elms. 216 00:42:48.480 --> 00:42:52.240 Mark Kushner: And so we plan to do this, well, we did this in NSCX, 217 00:42:52.360 --> 00:42:55.619 Mark Kushner: NSTX, and we plan to do this in NSTXU as well. 218 00:42:57.370 --> 00:43:10.649 Mark Kushner: Again, like I mentioned earlier, one of the other things is we're going to need non-inductive current drive, so we're also going to do that with our neutral beams, so we can drive our non-inductive current. One of the other things that is beneficial for spherical toggle mag is it has high bootstrap current. 219 00:43:10.650 --> 00:43:28.539 Mark Kushner: Bootstrap current is free or extra current, that you're not getting from your central solenoid-driven plasma current. Essentially, what it means is you have these trapped orbits here, and if you have a gradient in your particle density, which you will do, and that gradient is stronger in higher beta machines, such as spherical tokamaks. 220 00:43:28.540 --> 00:43:43.750 Mark Kushner: You'll have more particles on one leg or one side than the other, and if you have more particles going in one direction than the other, that's going to induce a current. And that current is then going to be transferred to passing particles, which go all the way around the donut by collisions. 221 00:43:43.750 --> 00:43:53.039 Mark Kushner: So, this current, the bootstrap current, naturally boosts your plasma current, because it's this free current that comes from this gradient in your density in your magnetic particles. 222 00:43:53.040 --> 00:43:58.419 Mark Kushner: So, we'll have this, as well as our neutral beam injected current drive. 223 00:43:58.600 --> 00:44:10.979 Mark Kushner: And so, with our neutral beams and the high bootstrap fraction that we expect in a spherical tokamak, the idea is being, oh, can we non-inductively, have current drive within our spherical tokamak? So that is not using, like, the central solenoid. And so… 224 00:44:11.230 --> 00:44:12.790 Mark Kushner: This is gonna be critical to show. 225 00:44:14.280 --> 00:44:34.259 Mark Kushner: Lastly, one of the few remaining things I'll talk about is relation to fast ions, because I focus on energetic particles. Fast ions can drive deleterious instability, so here's an example here from an experiment. This is a spectrogram of a magnetic coil, and all of these little color blotches, you can say, there's no need, are various instabilities within the plasma. 226 00:44:34.490 --> 00:44:53.329 Mark Kushner: And so, as again, I mentioned, gradients are a natural energy drive for instabilities. In this case, the gradient of your energy drive actually comes from your density gradient in your fast ions. Those fast ions are then higher than what we call the Alphane speed here, and if you look at this, 227 00:44:53.330 --> 00:45:10.539 Mark Kushner: this particle… wave-particle resonance here, which is simply just waves on a string, you'll find that all the conditions are met, you have a free energy source, you have a particle resonance, you have a dispersion relation to drive wave instabilities, and so you get all of these instabilities. There's quite a zoo of them. So these are all fast ion-driven instabilities. 228 00:45:10.560 --> 00:45:31.120 Mark Kushner: And what that means is these instabilities, they're driven by the fast ions, but they, in turn, can push and transport the fast ions themselves. So the fast ions start these instabilities, but the instabilities continue to push on them and push them outward. That leads to transport and losses. And so if you lose your fast ions, you're losing your current drive, you're losing your heating, and you're increasing your wall heat flux. So bad news bears. 229 00:45:31.740 --> 00:45:50.149 Mark Kushner: However, we want to try to use what we call phase-based engineering. So we have some knobs we can turn, for example, altering the fast line density profile using a second neutrobeam. You can see that previously we had all of these instabilities, we turned on a second neutrobeam, we cut them off and stopped them. So that's exactly what we want to do. We want to be able to control these instabilities. 230 00:45:50.150 --> 00:45:52.100 Mark Kushner: So the question we want to hope to probe is. 231 00:45:52.100 --> 00:46:06.160 Mark Kushner: How can we use our NBI and our RF antenna, our heating schemes, to preferentially heat and create our fast line population without controlling these instabilities? So we… so that we can maintain our current drive and maintain our plasma heating. 232 00:46:07.290 --> 00:46:32.210 Mark Kushner: Interestingly, another thing that we've only seen, this is, like, kind of hot off the press within the last year or so, is the interplay of fast ions and thermal confinement. And so, what we've observed is that fast ions can excite these modes, but these modes can also, in turn, drive zonal flows, and these zonal flows, as I mentioned earlier, can smooth out the plasma turbulence, and when they smooth out the plasma turbulence, your performance increases. And so that's what we see here. We have a mode here that drives down your turbulence. 233 00:46:32.210 --> 00:46:37.260 Mark Kushner: And then you have an increase in temperature. So something that we previously thought was bad for energetic particles. 234 00:46:37.260 --> 00:46:47.879 Mark Kushner: could actually be good for your thermal population, so it's probably going to be a balance between the two. The question is how much. And so, we did experiments a couple weeks ago, and we'll do some more experiments in NSTXU. 235 00:46:48.160 --> 00:46:59.659 Mark Kushner: These are some more obstacles we've yet to overcome, but they're all active solutions. We can talk about them later, but for the sake of time, I'll just push on so I can tell you all where's the field at in our final moments. 236 00:46:59.730 --> 00:47:17.949 Mark Kushner: Man, something happened with LaTeX, but for, some of you may have heard of this, but BigQ is our fusion energy gain factor. It's simply the ratio of our output fusion power relevant to our external heating power. So how much power are we getting out versus how much input power are we putting in? 237 00:47:17.950 --> 00:47:40.030 Mark Kushner: Obviously, if Q equals 1, that's break-even. Our magnetic confinement fusion record is about 0.67. You need about Q equals 5 to have a burning plasma with self-heating. That means the alpha particles are doing most of the self-heating relative to your external heating mechanisms. That's the neutral beam and your RF heating. And to actually produce a power plant, you need something like a factor of 15. 238 00:47:40.030 --> 00:47:50.130 Mark Kushner: And this here is kind of, all of the Fusion devices, or many of the Fusion devices. So this includes, Stellar Raiders, Tokamaks, spherical Tokamax, as well as just some ICF. 239 00:47:50.130 --> 00:48:00.619 Mark Kushner: And these contours here are the contours that we need for the loss in criterion to get Q greater than 1. And so you can see, we're kind of right on the edge there. Some of these have yet to be built, so don't treat them as fact. 240 00:48:01.650 --> 00:48:15.659 Mark Kushner: And again, this is kind of roughly scales in time, so you can put the same plot of NT tau, the three parameters trying to get, as a function of time, year, and you can see that we're slowly trajectorying upward, which is good. Progress, onwards and upwards. 241 00:48:15.680 --> 00:48:39.240 Mark Kushner: A nice, example to this, is it's analogous to Moore's Laws for transistors. So you may say… you may say, like, oh, this is quite slow progress, we've been working on this for decades, but it tracks relatively well with Moore's Laws for transistors, you know, saying that your transistors are going to double every two years, so you can see your transistors, as well as your NT tau for your various devices, are pretty much tracking. So. 242 00:48:39.240 --> 00:48:44.010 Mark Kushner: We're getting there. It's getting closer and closer, and we're just on the point of breakeven, I would say. 243 00:48:44.690 --> 00:48:54.899 Mark Kushner: If you're unfamiliar, there's Eater. This is, I'll call it the world's tokamak. It has various international members, US, China, Japan, EU, Korea, Russia, and India. 244 00:48:54.900 --> 00:49:05.149 Mark Kushner: This is being currently built in the south of France. It'll probably start somewhere in the mid-2030s. It'll be the largest tokamak, built to date. 245 00:49:05.150 --> 00:49:23.009 Mark Kushner: They're aiming for a queue of about 10 and an outward fusion power of about 500 megawatts. Of note, this is just purely a research device. If success with this, then they will go on to build a pilot plant, a fusion pilot plant, but we can… we could talk about that later. But you should be aware of it, because 246 00:49:23.030 --> 00:49:26.690 Mark Kushner: Construction is ongoing, and you know, some of our tax dollars go to it. 247 00:49:27.100 --> 00:49:38.730 Mark Kushner: As well as, over the past, I don't know, several years or so, there's been a huge explosive growth in private fusion enterprises. So, this is not all of them, but I've listed a great deal of them. 248 00:49:38.730 --> 00:49:48.640 Mark Kushner: I would say PBPL has some working relationship with almost all of them, and you can see they cover almost all of the confinement concepts that I've talked about today, so… 249 00:49:48.740 --> 00:50:00.630 Mark Kushner: at least one people, or several people, believe in various confinement scams, so, you know, choose your horse for who you want to win, but this has been an explosive growth in the field in the last, I'd say 5 years or so. 250 00:50:01.560 --> 00:50:06.960 Mark Kushner: Lastly, for how can you guys get involved, if I can promote you or entice you. 251 00:50:06.960 --> 00:50:29.670 Mark Kushner: We're always looking for undergraduates. We have SULI interns, which are summer interns every year. I highly encourage you to apply. I've had a summer intern in the past, I'll have a new one this year. I would say you're not limited to just fusion projects. There's heliophysics, astrophysics, inertial confinement, any project related to the plaza Physics is available at the lab. 252 00:50:30.410 --> 00:50:46.909 Mark Kushner: One of the examples, we actually had an intern, David Wegner, from Nuclear Engineering, from here, last year, who worked with a staff scientist on designing the lithium tiles that are going to go into NSCXU. So he designed them, prototyped them, and actually built this cool model. So, if there's any undergraduates, 253 00:50:47.070 --> 00:50:48.290 Mark Kushner: Please join us. 254 00:50:48.300 --> 00:51:04.330 Mark Kushner: Graduate students as well, please apply to graduate school at Princeton. You're going to apply to Princeton, you're going to apply through the program in Plaza Physics, which is part of the Astrophysical Sciences. So we get a herd of graduate students every year. You'll be usually paired for a first-year project, and they've shown great success in the past. 255 00:51:04.330 --> 00:51:18.180 Mark Kushner: We're also looking for postdocs. There's also the Strategic Science Initiative Fellowship, as well as the Robert A. Ellis Fellowship. These are open calls, you can essentially apply for anything, as well as there's always individual calls for postdocs, but we're always looking for postdocs, so… 256 00:51:18.470 --> 00:51:36.969 Mark Kushner: all the way from undergraduates to postdocs, please join us. So, our conclusions, I'm slowly running out of time. Why do we need fusion? Well, it's clean, it's abundant, it's energy efficient. What is it? Well, we're going to combine deuterium and tritium to produce helium-4 and neutrons in a hot plasma state. We need confinement, because fusion is slow relative to collisions. 257 00:51:36.970 --> 00:51:46.170 Mark Kushner: We're gonna do that with magnetic fields, of which there's many confinement schemes, but I'd say the most popular are Stellarator tokamak and spherical tokamak, all with their own advantages. 258 00:51:46.170 --> 00:52:02.309 Mark Kushner: I'd say the advantage of the Sumerical Tokamak, though, are that it's smaller, lower cost, higher beta, as well as possibly improved confinement, we'll have to see. We're handling the heat flux, we're handling the non-inductive current drive, we're also tackling fast ion instability, so we're all trying to solve a lot of problems. 259 00:52:02.670 --> 00:52:17.730 Mark Kushner: Many of you are asking, where are we? As I showed in those previous slots, we're very close, we're very close to break-even, but rapid progress, both in the public and private sectors, and everybody can, try to get involved, so… so thank you, and I'll take your questions, comments, so thanks for having me. 260 00:52:22.590 --> 00:52:26.230 Mark Kushner: Thank you very much. Are there questions? 261 00:52:27.530 --> 00:52:37.269 Mark Kushner: Great talk. So, you said you've worked on most every MCF sort of combined device. 262 00:52:38.750 --> 00:52:46.220 Mark Kushner: which one do you think, what's your… you said pick your horse, right? Yeah. What's your horse? Yeah, 263 00:52:46.700 --> 00:52:50.240 Mark Kushner: I mean, I'm definitely more in line with the… 264 00:52:51.010 --> 00:52:53.640 Mark Kushner: Spherical tokamak, Tokamak, and Stellarator, those are… 265 00:52:54.630 --> 00:53:11.169 Mark Kushner: the dominant three, I would say. The other ones, less so. But I think those all show… show great promise. Especially the spherical tokamak and the tokamak. Well, the spherical tokamak, especially if we can show some of these properties that we plan to do in Princeton in the next year, but the tokamak as well. 266 00:53:11.360 --> 00:53:29.190 Mark Kushner: In the long term, though, the Stellarator is rather advantageous. The engineering complexity, if that can get… if we can get over that, that's a… that's the hard part. The fact that there's no plasma current gets rid of all the… a lot of the stability properties and is a huge bonus. 267 00:53:29.370 --> 00:53:34.389 Mark Kushner: But yeah, it's the engineering, so… I mentioned that we can have this optimization for stellarators. 268 00:53:34.390 --> 00:53:51.519 Mark Kushner: And numerically, that's shown really great promise. But I guess the question is, how accurately can we build one of these optimization stellarators, and with what tolerance? So, they may say, oh, we can build this machine with these specs, but if the tolerance is insane, it could be difficult, so… 269 00:53:51.620 --> 00:53:56.959 Mark Kushner: Yeah, I'd be in favor of those three, but it might give an edge to Spherical Tokamak and Tokamag. 270 00:53:57.800 --> 00:53:58.679 Mark Kushner: Oh, yeah. 271 00:53:58.850 --> 00:54:18.330 Mark Kushner: So, as the… you mentioned the commercialization ramping up in the last few years, what do you think that's doing to the field regarding, sort of, openness, in terms of, you know, are there now, you know, IP issues that rise in new developments of any given company that then don't get out in the public sphere? 272 00:54:18.430 --> 00:54:29.750 Mark Kushner: That could help accelerate us all. Yeah. Are you sensing a little bit more… it seems like the volume of money coming in from the private sector is probably exceeding how the 273 00:54:29.750 --> 00:54:39.390 Mark Kushner: Yeah, it's an interesting question, and I would say it's also continually evolving, because a lot of these, like, public-private partnerships are… 274 00:54:39.700 --> 00:54:41.919 Mark Kushner: Are still relatively new, or ongoing. 275 00:54:42.130 --> 00:54:56.530 Mark Kushner: I would say it also depends on the company. Some companies are a lot more open than others. Like, some openly publish and share their results. Others don't publish at all. So, from the public perspective, we have no idea what they're doing behind closed doors, or whatever their technology is. 276 00:54:56.530 --> 00:55:03.240 Mark Kushner: Which is hard to believe upon in fusion, when someone makes great claims and you don't have the evidence to back it up. 277 00:55:03.240 --> 00:55:13.819 Mark Kushner: I will say, though, from… I've worked on projects with two, companies, and they've been very forthright in sharing stuff, and we've published stuff with them. 278 00:55:13.860 --> 00:55:29.629 Mark Kushner: So it depends on company to company. They all kind of have a secret sauce, though, that they want to keep to themselves, but in terms of, like, the basic fusion science and basic physics, there are groups that are willing to 279 00:55:29.760 --> 00:55:33.650 Mark Kushner: share that publicly and such. And especially if… 280 00:55:33.880 --> 00:55:42.460 Mark Kushner: I would say, like, from the public side, if they want to do, like, a partnership, especially if it's, like, a financial partnership through, like, a DOE grant or something. 281 00:55:42.560 --> 00:55:59.059 Mark Kushner: there is, like, a component that, like, they have to be open about it. They can't get, like, public expertise or public usage of codes or something like that, and just keep it all to themselves. So there is… but it's interesting, because a lot of these agreements are being created, kind of, like, as we speak, so… 282 00:55:59.060 --> 00:56:05.080 Mark Kushner: There's also a lot of, legalese and stuff that the lawyers argue back and forth on, yeah. 283 00:56:07.760 --> 00:56:13.519 Mark Kushner: There seems to be a bit of a perception from outside 284 00:56:13.620 --> 00:56:25.140 Mark Kushner: PPL of lots of technical issues with NSTX, and hasn't been operated for a long time. I'm not an expert, but, you know, I wonder if you could 285 00:56:25.140 --> 00:56:44.330 Mark Kushner: comment on those technical problems for many years, and what… were they resolved? What would be operational? Yeah, so there were technical issues back in 2016, which is before I started the lab. And as a result of that, we've gone through, like, a full upgrade, so we're completely redoing, replacing the center stack. 286 00:56:44.410 --> 00:56:57.839 Mark Kushner: I'm not involved as a part of this refurbishment or reconstruction process, and I know they're actively working towards solutions. And they're, they're very… Still a problem? 287 00:56:58.200 --> 00:57:05.279 Mark Kushner: No, well, we believe we've resolved everything, so yeah. But it should be fixed in a year or so. 288 00:57:05.780 --> 00:57:14.260 Mark Kushner: That kind of leads to a question that that was also a problem for scaling us up to a fusion power plant through the center stack, and it's… 289 00:57:14.270 --> 00:57:26.669 Mark Kushner: kind of… kind of, exposed nature, you know? Yeah. Is there a solution to that? I believe so, yes. Because I think the issue, I'm not 100% certain, because it was before my time. 290 00:57:26.990 --> 00:57:37.359 Mark Kushner: the issue was, like, an engineering issue that was solved. I mean, but scaling the whole thing up to a power plant. Oh. Could you actually… could the center stack survive? 291 00:57:37.700 --> 00:57:46.610 Mark Kushner: in the… with the, you know, superconducting coils or something inside the… inside that kind of cordon? Yes, I believe so, yes. 292 00:57:46.890 --> 00:57:57.709 Mark Kushner: I mean, there are private fusion companies that are investigating that, so notably Tokamak Energy in the UK, who are designing a fusion pilot plant that is a spherical Tokamak. 293 00:57:57.920 --> 00:57:59.550 Mark Kushner: Yeah. 294 00:58:00.810 --> 00:58:07.799 Mark Kushner: So, I mean, everything remains to be seen until it's built. So, yeah, that's one of the issues with the field. 295 00:58:10.340 --> 00:58:14.829 Mark Kushner: So I guess I have two related questions. One… one would be… 296 00:58:15.750 --> 00:58:19.660 Mark Kushner: From your point of view, how much… 297 00:58:19.930 --> 00:58:28.269 Mark Kushner: Thought has been given to the issue of when you transition to deuterium tritium, and now you're irradiating 298 00:58:28.900 --> 00:58:42.560 Mark Kushner: your central stack, or with CFS, the wall loading and whatnot with 14 MeV neutrons. So that'd be one question. They're simple questions, so you'll probably be able to remember both. The other is, when you were talking about 299 00:58:42.710 --> 00:58:50.359 Mark Kushner: building… the coils for the stellarators in that shape. I'm just wondering if you've looked much 300 00:58:50.400 --> 00:59:05.860 Mark Kushner: at the practicality of, I think it's Thea? Yeah. Where they're actually talking about doing the planar coils so that they can actually tune the, the shape, rather than being stuck with a manufactured shape. 301 00:59:06.090 --> 00:59:24.010 Mark Kushner: Yeah, okay, to your first question about, like, DT and neutrons, yes, no, that's actively thought about a lot, investigated a lot. As I mentioned, DT experiments are not common, so unfortunately, there's not a lot of data. I know a lot of us are relying on the recent JET experiments, 302 00:59:24.130 --> 00:59:29.079 Mark Kushner: as well as I know some people are going back to the TFTR experiments from the 1990s. 303 00:59:29.210 --> 00:59:32.559 Mark Kushner: But people are thinking about it, 304 00:59:33.410 --> 00:59:42.910 Mark Kushner: Yeah, people… it's mainly through modeling, I would say, though. But yeah, people are aware of when they go to DT, they're gonna have the neutron and the tritium as well. 305 00:59:43.090 --> 01:00:02.459 Mark Kushner: And Rosethea, yes, I'm aware of it. They're actually one of the people I've worked with and published with, so I'm aware of their concept. It is, I'd say intriguing and positive, in the sense that, yeah, so for those of you unfamiliar, instead of creating, like, those complex 306 01:00:02.460 --> 01:00:17.819 Mark Kushner: Stellarator coils that are kind of twisted, they're gonna put small planar coils all over the machine. And so by having all of these coils everywhere, essentially, they can use that to inherently create their 3D magnetic structure for their stellarator. So it's… 307 01:00:17.990 --> 01:00:25.919 Mark Kushner: It's a simpler design from the engineering aspect of the coils, but maybe more complex, because you have to have all of these coils working together. 308 01:00:26.030 --> 01:00:39.490 Mark Kushner: I think it's promising, from the work I've seen with them. They have optimized equilibria, and things look good. But yeah, and I also think I've seen some recent work of them where they have some nice, 309 01:00:39.640 --> 01:00:47.180 Mark Kushner: engineering work with their recent coils and active feedback. But yeah, it's an exciting idea, I think. 310 01:00:51.510 --> 01:00:53.230 Mark Kushner: Any other questions? 311 01:00:55.010 --> 01:01:05.009 Mark Kushner: This is related to what we were talking about earlier, but so, you're using, 312 01:01:05.470 --> 01:01:19.799 Mark Kushner: Nstx is using liquid lithium as a plastofasing material now. Eventually. Eventually. Yes. Is that also related at all to anything to do with tritium breeding? Or is that just, it's also convenient for it? 313 01:01:19.940 --> 01:01:29.990 Mark Kushner: I guess it's also convenient for it. No, the liquid lithium that will be used to, like, coat the wall and diverter is mainly to handle the heat flux. Okay. And so ideally, I guess. 314 01:01:30.020 --> 01:01:50.839 Mark Kushner: on the outside, so you'd have your liquid lithium as your first plasma-facing component that handles the heat flux and your impurity, recycling and whatnot. Then you have your wall, then you have, like, your water blanket that you use for fusion power, and then also you have your liquid lithium blanket for your tritium production, which is also… that's another open question in the field, if we go back to… 315 01:01:51.820 --> 01:02:03.400 Mark Kushner: Other problems? So, like, the… oh, there's a delay here. Tritium breeding and the whole tritium fuel cycle has never been demonstrated, so we can rely on past experiments, but that is something the field as a whole has to answer. 316 01:02:03.900 --> 01:02:21.199 Mark Kushner: So, yeah. Then, I guess, other smaller question, would… if you're going through the trouble of dealing with liquid lithium, I guess this would not be NSTX-specific, but are there any reactors that are trying to use liquid lithium as a coolant to try to solve both of those problems at the same time? 317 01:02:21.470 --> 01:02:28.829 Mark Kushner: What do you mean as a coolant? Like, both the, like, neutron capture for power production, and also producing tritium. 318 01:02:28.890 --> 01:02:42.730 Mark Kushner: Not that I'm aware of, because you'd probably, might be… I'm not an expert at the liquid lithium, but my guess would be that you'd need more liquid lithium, and if you had too much, it's going to create engineering complex… complexities, yeah. 319 01:02:43.260 --> 01:02:44.820 Mark Kushner: Thank you. 320 01:02:47.000 --> 01:02:58.070 Mark Kushner: So, yeah, you mentioned that DT experiments are rare, in magnetic confusion, and I guess I have two questions. One is… 321 01:02:58.120 --> 01:03:08.339 Mark Kushner: Why? It's the reason for their rarity, and, because PT experiments are somewhat common in ICF, right? 322 01:03:08.820 --> 01:03:19.530 Mark Kushner: one-on-one. And so, can some of the results that SNP is learning about ET reactions help inform 323 01:03:19.890 --> 01:03:23.779 Mark Kushner: Some of the… the modeling that… that you all are doing. 324 01:03:23.900 --> 01:03:28.730 Mark Kushner: to try and maybe reduce risk of some of those DT experiments that I'm seeing. 325 01:03:28.980 --> 01:03:40.450 Mark Kushner: in terms of plasma physics, I want to say no, because the plasmas are completely different, right? You're at significantly higher densities, completely different temperatures. So in terms of the physics, I want to say no, but in terms of, like. 326 01:03:41.130 --> 01:03:46.220 Mark Kushner: The tritium activation, and maybe, like, material science and, 327 01:03:46.390 --> 01:03:50.580 Mark Kushner: You know, engineering properties that you'll have in your facility, probably, yeah. 328 01:03:50.890 --> 01:03:58.019 Mark Kushner: Sorry, what was your other question? Why are they rare? Oh, why are they rare? Okay, well, the first is, 329 01:03:58.270 --> 01:04:10.110 Mark Kushner: how should I put it? Regulations is part of it, so rules, unfortunately. You have to be, you know, you're dealing with a radioactive substance, so it creates a more bureaucratic headache. 330 01:04:10.310 --> 01:04:16.319 Mark Kushner: As well as, I think, probably just general cost is a lot more expensive than doing DD. 331 01:04:16.480 --> 01:04:25.609 Mark Kushner: Okay, great. And I think we have one last question online. So John, either unmute yourself or type in the chat. 332 01:04:26.340 --> 01:04:27.840 John Verboncoeur: Okay, can you hear me? 333 01:04:28.350 --> 01:04:29.040 Mark Kushner: Yes? 334 01:04:29.480 --> 01:04:39.890 John Verboncoeur: Okay, so I have more of an economic question. So, Eater is expected to have to scale by, let's say, a ballpark factor of 2. 335 01:04:39.970 --> 01:04:54.319 John Verboncoeur: To, to achieve an economic fusion reactor, just based on what we know so far. And that really means roughly 8 times in cost, so we're looking at, north of $240-ish billion. 336 01:04:54.320 --> 01:05:00.699 John Verboncoeur: Can you tell us a little bit about the scaling of the SphereMac with respect to that? 337 01:05:00.730 --> 01:05:06.029 John Verboncoeur: And other schemes as well, if you want to comment on those. 338 01:05:06.180 --> 01:05:15.780 John Verboncoeur: just in terms of where you expect that to be based on current knowledge. I understand that we don't have as much experimental knowledge yet, but nevertheless, if you could make some estimates. 339 01:05:16.990 --> 01:05:20.870 Mark Kushner: Good question, yes. Always boils down to money, doesn't it? . 340 01:05:20.870 --> 01:05:22.330 John Verboncoeur: Energy's a commodity. 341 01:05:22.330 --> 01:05:25.200 Mark Kushner: Yeah, I will say any… 342 01:05:25.640 --> 01:05:35.180 Mark Kushner: anything and everything is going to be cheaper than Eater by a long shot. Eater is enormously expensive, in part due to its size. 343 01:05:35.290 --> 01:05:38.499 Mark Kushner: Yeah, in terms of numbers. 344 01:05:38.520 --> 01:05:44.650 Mark Kushner: I mean, many fusion companies and public sector machines, they can be built for, like. 345 01:05:44.650 --> 01:06:03.570 Mark Kushner: 10… on the orders of tens of millions of dollars. I mean, you can look at many of the private fusion companies that already exist. They're already actively building their machines, and they don't have nearly enough the same, you know, capital, in terms of billions of dollars. So, in theory, it's gonna be… all the other devices are gonna be significantly cheaper. 346 01:06:03.650 --> 01:06:05.220 Mark Kushner: Yeah. 347 01:06:06.220 --> 01:06:15.050 John Verboncoeur: Well, I guess I was looking for not an experimental number, but a production number, so if we compare it to a fission plant, for example, it's multiple billions. 348 01:06:16.310 --> 01:06:17.819 Mark Kushner: Sorry, it's hard to hear you. 349 01:06:17.990 --> 01:06:25.170 John Verboncoeur: A fission plant would cost multiple billions to produce, let's say, 500 to 1,000 megawatts. 350 01:06:25.170 --> 01:06:31.070 Mark Kushner: Yeah, comparing to, like, a fission plant. That's a good question. 351 01:06:31.440 --> 01:06:36.360 Mark Kushner: I mean, if I want to punt, I can say it depends on which confinement scheme you're choosing, and 352 01:06:36.610 --> 01:06:42.689 Mark Kushner: Which of these, which of these companies are building it? 353 01:06:42.870 --> 01:06:47.770 Mark Kushner: Some of these… Are gonna be certainly cheaper than a billion dollars to build. 354 01:06:47.800 --> 01:07:02.239 Mark Kushner: Other words… other ones can, you know, maybe get up there on the pilot plant scale, but I… I think they're gonna be cheaper to produce, and as well as there's evolving technology as well, like, so… Tokamak Energy and Commonwealth Fusion Systems with their high-temperature superconductors. 355 01:07:02.240 --> 01:07:08.400 Mark Kushner: They've really shrunk the device size, which has greatly reduced the construction costs. So… 356 01:07:08.620 --> 01:07:12.519 Mark Kushner: I think things will be cheaper, but who knows? Time will tell. 357 01:07:13.660 --> 01:07:14.469 John Verboncoeur: Okay, thanks. 358 01:07:15.830 --> 01:07:19.039 Mark Kushner: Okay. Oh, Bill, thank you so much. No, thank you. 359 01:07:30.050 --> 01:07:32.700 Mark Kushner: Yeah, Larry? 360 01:07:32.810 --> 01:07:36.960 Mark Kushner: Thank you.