Dr. David Kirtley on Lex Fridman: Why the H-bomb is fission

1. 0:00 – 3:14

   Introduction

   1. LFLex Fridman0:00

      The following is a conversation with David Kirtley, a nuclear engineer, expert on nuclear fusion, and the CEO of Helion Energy, a company working on building nuclear fusion reactors and have made incredible progress in a short period of time that make, uh, it seem possible, like we could actually get there as a civilization. This is exciting because nuclear fusion, if achieved commercially, will solve most of our energy needs in a clean, safe way, providing virtually unlimited clean electricity. The problem is that fusion is incredibly difficult to achieve. You need to heat hydrogen to over 100 million degrees Celsius and contain it long enough for atoms to fuse. That's why the joke in the past has been that fusion is 30 years away and always will be. Just in case you're not familiar, let me clarify the difference between nuclear fusion and nuclear fission. By the way, I believe according to the excellent Sample Size subreddit post by pmgoodbeer on this, the preferred pronunciation of the latter in US is nuclear fi-sion, like vision, and in the UK and other countries is nuclear fi-ssion, like mission. I prefer the nuclear fi-sion pronunciation because America. So, uh, today's nuclear power plants use nuclear fi-sion. They, uh, split apart, heavy uranium atoms to release energy. Fusion does the opposite. It combines light hydrogen atoms together, the same reaction that powers the sun and the stars. The result is that it's clean fuel from water, no long-lived radioactive waste, inherently safe because a fusion reactor can't melt down. If, uh, something goes wrong, the reactor simply stops, and there's, uh, no carbon emissions. On a more technical side, Helion uses a different approach to fusion than has traditionally been done. Most fusion efforts have used tokamaks, which are these giant donut-shaped magnetic containment chambers. Helion uses pulsed magnetoinertial fusion. David gets into the super technical physics and engineering details in this episode, which was fun and fascinating. I think it's important to remember that for all of human history, we've been limited by energy scarcity. And every major leap in civilization, agriculture, industrialization, the information age, came in part from unlocking new energy sources. If someone is able to solve commercial fusion, we would enter a new era of energy abundance that fundamentally changes what's possible for us humans. I'm excited for the future, and I'm excited for super technical physics, uh, podcast episodes. This is a Lex Friedman podcast. To support it, please check out our sponsors in the description where you can also find links to contact me, ask questions, give feedback, and so on. And now, dear friends, here's David Kirtley.

2. 3:14 – 13:14

   Nuclear fission vs fusion

   1. LFLex Fridman3:14

      Let's start with the big picture. What is nuclear fusion, and maybe what is nuclear fission? Uh, let's lay out the basics.

   2. DKDavid Kirtley3:22

      So fusion is what powers the universe. Fusion is what happens in stars, and it's where the vast amount of energy that even that we use today here on Earth comes from the process of fusion. It also is what powers plants, and those plants become oil, and those become fossil fuels that then powers the rest of human civilization for the last 100 years. And so fusion really underpins a lot of what has enabled us as humans to go forward. However, ironically, we don't do it actively here on Earth to make electricity yet. And so fundamentally, what fusion is, is taking the most common elements in the universe, hydrogen and lightweight isotopes of hydrogen and helium, and fusing those together to make heavier elements. In that process, as you combine atomic nuclei and form heavier nuclei, those nuclei are slightly lighter than the sum of the parts. And that comes from a lot of the details of quantum mechanics and how those fundamental particles combine and interact. Um, we also talk about the strong nuclear force that holds the atomic nucleuses together as one of the fundamental forces involved in fusion. But that mass defect, E equals MC squared, we know from Einstein, is also energy. And so in that process, a tremendous amount of energy is released. And the actual reactions, I think, is a lot more interesting than simply it's a little bit lighter and therefore energy is released. But that's the fundamental process in fusion as you're bringing those, those lightweight atomic nuclei, those isotopes together. Fission is the exact opposite, where you're taking the heaviest elements in the universe, uranium, plutonium, things that are so heavy and have so many internal protons and neutrons and electrons, that they're barely held together at all. They're fundamentally unstable or radioactive. And those elements are very close to falling apart. And as they do that, if you take a uranium-235 or a plutonium-239 nucleus and you add something new, usually it's a neutron, a subatomic particle that's uncharged, that unstable, that very large nuclei will then break into pieces, many pieces, a whole spectrum of pieces. But if you add up all of those pieces, they also have slightly less mass than the initial one did, the initial uranium or plutonium. And in that process, again, E equals MC squared, a tremendous amount of energy is released. There's a very famous curve in atomic physics, fusion or fission, looking at the periodic table, going from the lightest elements, hydrogen, to the heaviest elements, those uranium, plutonium, and others. And fusion happens up to iron. Iron is the magical point in between where lighter elements than iron fuse together and heavier elements-... fizz, or, uh, are fissile and break apart and release energy. I think about and I look at that process, uh, in stars, in that our star is fundamentally an early stage star that's burning just hydrogens. But when it burns and does fusion, those hydrogens combine into heliums, and later stage stars can then burn those heliums, and they can fuse those together to form even heavier elements and carbons. And those carbons can fuse together and form heavier elements. And, um, that whole stellar process is something that inspires us, uh, at Helion to think about what are fusion fuels, not just the simplest ones, but more advanced fusion fuels that we see in stars throughout the universe.

   3. LFLex Fridman6:59

      Okay, so there's a million things I want to say. So first, maybe zooming out to the biggest possible picture. If we look across hundreds of millions, billions of years, and all the, my opinion, alien civilizations that are out there, they're going to be powered likely by fusion. So our advanced intelligent civilization is powered by fusion, in that the sun is our power plant.

   4. DKDavid Kirtley7:21

      Mm-hmm.

   5. LFLex Fridman7:22

      Uh, then the other thing is the physics. Again, very basic, but you said E equals MC squared a couple times.

   6. DKDavid Kirtley7:28

      Mm-hmm.

   7. LFLex Fridman7:29

      Can you explain this equation?

   8. DKDavid Kirtley7:30

      E equals MC squared is a fundamental relationship that a patent clerk, Einstein, discovered, and unlocked an entire new realm of physics and engineering, and has shown us atomic physics, what happens inside the nucleus, and unlocked our understanding of the universe, and paved the way for many of the physics advancements that came after, that we think about mass as these particles. But in reality also, at the same time, they're energy, and there's a direct quantitative relationship between how much energy is in all of that mass. And in fact, all of the energy that is released, even by, uh, by atomic physics, sur- certainly in atomic reactions, is E equals MC squared, and that, that I think most people are, have heard of and are use- used to. But also in chemistry and in chemical bonds, that in those chemical bonds, there is a change in mass. When you take a hydrogen and an oxygen and you burn them and you combine them into water, there's a change in mass. Now, that change per atom and per molecule is actually so small that it's extremely hard to measure, but, but it's still there, and that's the energy that is released, and you can quantify that. We use, uh, units of electronvolts, um, as a unit of what is the energy in atomic processes or chemical processes.

   9. LFLex Fridman8:53

      Can you also just speak to the, the different fuels that you mentioned, both on the fusion and the-

   10. DKDavid Kirtley8:58

       Mm-hmm.

   11. LFLex Fridman8:58

       ... fission side? So uranium, plutonium for the fission, and then hydrogen isotopes for the fusion.

   12. DKDavid Kirtley9:04

       So for fission, uranium and plutonium, we don't make those nuclei. Those, right now, for humanity, those have been made in the primordial universe through ser- supernova and Big Bang, um, and the initial formation of the universe where matter was created, and so we dig those up. We dig up uranium, plutonium out of the ground. Um, and in fact, most plutonium we make from uranium, and we can talk about how to enrich, uh, uranium if we, if we want to go down that road, but that's how we get those molecules and nuclei. For fusion materials, hydrogenetic species or hydrogens, um, are primordial in the universe also, only the most common things that are in the universe. Uh, the su- suns and stars are made up of hydrogens and heliums, um, and so the vast majority of atoms in the universe still are hydrogen.

   13. LFLex Fridman9:57

       So the basic fuel for fission is already in the ground, and then the basic fuel for fusion is everywhere.

   14. DKDavid Kirtley10:02

       Is everywhere, and we particularly use a type of hydrogen called deuterium, which is a heavier isotope of hydrogen. Hydrogen is typically one proton and one electron, atomic mass of one. Deuterium has an atomic mass of two, which is a proton, which is a charged particle, and it has a neutron in its nucleus, which is an uncharged particle. And so that's deuterium as the fuel. Now deuterium is also found in all water on Earth, in the water I'm drinking right now. It's in my body. It's in Coca-Cola.

   15. LFLex Fridman10:32

       Mm-hmm.

   16. DKDavid Kirtley10:32

       Um, it's, it's, it's everywhere. Um, and, and safe and clean and, and one of those fundamental particles that was born in the cosmos, and we estimate that in seawater here on Earth, we have, if we powered at our current use of electricity all of humanity on fusion, somewhere between 100 million years and a billion years of fuel in hydrogen and deuterium here on Earth.

   17. LFLex Fridman11:00

       And how is that stored mostly?

   18. DKDavid Kirtley11:02

       And mostly that's just in water. Mostly that it's a mix of... We, we call this actually heavy water, where you have normal water that you're used to, uh, we talk about and you learn in school as H2O, where there's two hydrogens and an oxygen in a nucleus in the molecule, and deuterium or heavy water is D2O, two deuteriums and an oxygen. Um, in reality, it's actually an interesting mix, uh, where you have some HDO, so a mix of hydrogen and deuterium. You also have other hydrogenetic species. Tritium is another one, where you add a second neutron to that hydrogen, and then you can have T2O, tritiated water, um, and that's something that, that comes up and, and, and we need to talk about at some point. Um, and there's other... As you go up the periodic table, you get, add two protons and you get helium, and so helium, the most common helium is, is helium-4, which is two protons and two neutrons, and then we use an isotope of helium. The nucleus is called helion, which is what we based the company after, which is two protons and one neutron. It's a light helium molecule.

   19. LFLex Fridman12:07

       So the number you mentioned in terms of, uh, how much fuel is available, basically the, the takeaway there is it's a nearly endless resource.... in terms of fuel. Is that correct to say?

   20. DKDavid Kirtley12:19

       That's correct to say at today's power level. I think what's interesting is the idea that as we deploy the same power source that powers the universe here on Earth, as humans, can we do more? Can we have access to much more electricity and much more energy and do really interesting things with that? And still there's large amounts, millions and millions of years of power, um, even at much higher output power levels for humanity.

   21. LFLex Fridman12:45

       Yeah, so the moment we start running out of, uh, (laughs) hydrogen and helium where (laughs) -

   22. DKDavid Kirtley12:50

       Mm-hmm.

   23. LFLex Fridman12:50

       ... that means we're doing some pretty incredible things with th- with, with our technology. And then that technology is probably gonna allow us to propagate out into the universe and then discover other sources. 'Cause you can also get it on other planets.

   24. DKDavid Kirtley13:02

       Yeah.

   25. LFLex Fridman13:02

       Whatever planets have water, and it looks more and more likely like a lot of them do, what a incredible future, just out into the cosmos, nuclear power plants everywhere.

3. 13:14 – 18:28

   Physics of E=mc^2

   1. LFLex Fridman13:14

   2. DKDavid Kirtley13:14

      Yeah.

   3. LFLex Fridman13:14

      Okay. So, uh, to linger on the- some of the technical stuff, you said, uh, strong nuclear force. So how exactly is the energy created? So how does the E equals MC squared, the, the M go to the E, uh, in fusion?

   4. DKDavid Kirtley13:31

      So in fusion, you take these lightweight isotopes like hydrogen and deuterium, and as you combine them and get- and take these molecules and get them closer and closer together, some really interesting fundamental physics happens. So first, um, these atomic nuclei are charged. They have an electric charge, and they, like charges repel. And I think everybody is familiar with that, where you take two positive charges, and you try to push them together, and the electromagnetic force between them repels them. So you have a force that's actually pushing against them. So in fusion, you work to get your fuel very hot, very, very high temperatures, 100 million degree temperatures. And temperature really is kinetic energy. It's motion, it's velocity, so that these particles are moving so fast that even though they're coming together and there's this repulsive electromagnetic force, they can still come close enough that another force comes into play, which is the strong force. Um, and then once you get within a very close distance on the order of the scale of those nuclei themselves, of those atomic nuclei, so the tiniest thing you could imagine and probably way smaller than that, these particles then are attracted to each other, and they combine, and they fuse together. At that point, you create heavier atomic nuclei that have a slightly less mass, slightly less total mass in the system, and that mass equals MC squared as energy.

   5. LFLex Fridman14:55

      So extremely high temperature, extremely high speed, uh, maybe that's one of the other differences also with fusion and fission is just the amount of temperature required for the reactions. Is that accurate to say?

   6. DKDavid Kirtley15:07

      Yeah, and I think fundamentally, it's that in a lot of ways, fusion is hard, and fission is easy.

   7. LFLex Fridman15:14

      Yeah.

   8. DKDavid Kirtley15:14

      Nuclear fission happens at room temperature, that this uranium and plutonium is so likely to break apart already that simply the adding of one of these neutrons, one extra particle will then break it apart and release energy. Um, and if you have a lot of them together, it will create a chain reaction. Fusion, that doesn't happen at all. Fusion is actually really hard to do. You have to overcome those electromagnetic forces to have a single fusion reaction happen. Um, and so it takes things like in our sun we have what is called gravitational confinement, where the gravity, literally the mass of the fuel itself is pulling to the center of the sun, and it's pulling. And so there's a large force that's pulling all that fuel together and, and, and holding it and confining it together such that it gets close enough and hot enough for long enough that fusion happens.

   9. LFLex Fridman16:07

      And then we have to figure out if we're, uh, building fusion reactors, we have to figure out how to do that confinement without the huge, uh, size gravity of the sun.

   10. DKDavid Kirtley16:18

       That's right. Obviously, the sun is vastly larger than Earth. And so we can't do that same process here on Earth.

   11. LFLex Fridman16:25

       Yet. No, I'm just kidding. All right.

   12. DKDavid Kirtley16:27

       But we have other forces we get to use. We can use the electromagnetic force, which the sun doesn't get to do, to apply those forces. And I actually want to take a pause right there and point out a word. Historically, we've used the word reactor around fusion, but I don't think that's right. And for me, we're really careful about this terminology.

   13. LFLex Fridman16:47

       Mm-hmm.

   14. DKDavid Kirtley16:47

       Um, when we look to how that word is defined, and we can look to how the experts define it, it doesn't really apply to fusion. Um, so the Nuclear Regulatory Commission, the NRC, uh, defines reactor as, I have it, I have it right here. "A nuclear reactor is an apparatus other than an atomic weapon designed or used to sustain nuclear fission in a self-supporting chain reaction." And there's two big parts to that, that one, fission reaction. Obviously, fusion is not that, and we've talked about why, but also the self-sustaining part, in that a reactor is self-sustaining. You take your hands off of it, and it keeps going. In fusion, that doesn't happen, and, uh, and we know 'cause we have to do it every day, and it's really hard to do. And so we actually use the word generator, because you- we don't talk about, for instance, a natural gas reactor is that if you stop putting in fuel, it turns off. And the same thing happens in fusion, and so we'll- we're, we're pretty careful about making sure we talk about that as a generator where you're putting in fuel, you're getting electricity out. Um, and then when you stop putting in fuel, it just shuts off, and you can go even one step further and say, "What am I gonna do with this fusion that powers the universe? And what does humanity want out of this?" And what we want is electricity. We don't simply want a set of reactions, um, or even heat and energy. That's great, but what I really want is electricity.

   15. LFLex Fridman18:12

       And, uh, yeah, we'll talk about the technical details of one of the big benefits of the linear design of the approach that you do is you get to electricity directly a- as quickly as possible. And some of the other alternatives, um, have a intermediate step, and those again are, are

4. 18:28 – 23:50

   Is nuclear fusion safe?

   1. LFLex Fridman18:28

      technical details, but let me sort of still linger on the difference between-

   2. DKDavid Kirtley18:32

      Mm-hmm.

   3. LFLex Fridman18:32

      ... fusion and fission. Uh, what are some advantages at a high level of nuclear fusion as a source of energy?

   4. DKDavid Kirtley18:38

      ... fundamentally as, as a source of energy. In fusion, you're taking these lightweight isotopes, you're bringing them together, you're releasing energy, and that energy is in the form of charged particles. It's already in the form of electricity. Fusion itself has electricity built into it, without a lot of the steam or thermal system requirements. And so that's a really nice fundamental benefit of fusion itself. Also, this reaction that's really hard to do turns itself off, so you end up with that fusion is fundamentally safe, and that's really a key requirement of any industrial system is that it turns itself off and it's safe. You turn the key off on your car, you know it's gonna turn off.

   5. LFLex Fridman19:20

      I guess the, the flip side of that, just sort of s- stating the obvious, but it's nice to lay it out. For nuclear fission, it's a chain reaction, so it's hard to shut off, and it works by boiling water into steam, which spins turbines and produces electricity. Can you talk through this process in a nuclear fission reactor?

   6. DKDavid Kirtley19:43

      In a nuclear fission reactor, you put enough of this fissile material, uranium or plutonium, together such that as these unstable molecules, these unstable atoms crack open and break apart, they release heat, that the component parts of those are actually quite hot. And so not only are the component parts that the uranium breaks into, and it's a whole spectrum of different atoms and atomic nuclei, are hot, but it also releases neutrons. It also releases more of these uncharged particles. And if you do it right, this fissile material will be next to other fissile material, and so that neutron will then go and bombard another uranium nucleus, again opening that up and releasing more heat and more of these neutrons. And that's how you have those reactions of a self-supporting chain reaction, and that chain reaction then continues. People design fission reactors such that you have just the right balance of enough neutrons are made such that the reaction is continuing, but not so many neutrons are made that it speeds up-

   7. LFLex Fridman20:48

      Mm-hmm.

   8. DKDavid Kirtley20:48

      ... 'cause you don't want it to speed up.

   9. LFLex Fridman20:50

      And there's some kind of cooling mechanisms also? Like, that's part of the, the art and the engineering of it?

   10. DKDavid Kirtley20:56

       And then the key is at the same time you want to make sure that the whole thing is in water, is typically the cooling fluid. There's some more advanced fission reactors that have different cooling fluids, but water typically, where then that absorbs that both the heat and those extra neutrons. And so you use the water and the fluid to then run a steam turbine to do traditional electricity generation and, and output electricity through your, your steam turbine. You end up with complicated systems of flowing liquids and flowing water, balancing the heat. A lot of fission reactor design comes from that thermal balance of keeping this reaction going, making sure it doesn't speed up 'cause that's, that's an un- uh, controlled chain reaction, which you would not want, and balancing the, the cooling and the output of getting the water out of it.

   11. LFLex Fridman21:48

       So we should say that for reasons you already laid out, maybe you can speak to it a bit more, is nuclear fusion is much safer. So there's no chain reaction going on. You can just shut it off. But it should also be said that as far as I understand, the current fission nuclear reactors are also very safe. I think there's a perception that nuclear fission reactors are unsafe, they're, they're dangerous, and if you just look empirically at the statistics that the fear is not justified by the actual safety data. Can you just speak to that a little bit?

   12. DKDavid Kirtley22:22

       Yeah, we've been talking about the reaction processes themselves, but I think fundamentally let's take a step back and look a little broader and say let's look at what we care about, which is the power plant, making electricity. And I look at this from a nuclear engineer's point of view. I spent a lot of years studying these, these systems. Um, and modern fission reactors, I believe, are s- are engineered to be safe. They're engineered in ways where as those, uh, reactions maybe speed up and those systems get hotter, they actually are built to expand and cool down passively and natively. And there's protection systems in place that modern systems are quite safe from an engineering perspective. And so I believe that we have figured out how to build nuclear fission reactors in a way where the engineering of the power plant is safe. I would say that I look back at the history of what we've built over time and the challenge hasn't come to the engineering, actually. I believe the engineers have solved these problems. Uh, the problem comes from humans, and the problem comes from other things around nuclear power. You have to enrich that uranium to put it in a plant. And the plant's safe, but you had to enrich that uranium, and that is some of the problem. Or a plant is designed to run for a certain number of decades safely, but do we run it longer than that? And so those are where I think the real challenges happen is more with the humans around these systems than the engineering of the power plants themselves.

5. 23:50 – 30:17

   Chernobyl

   1. DKDavid Kirtley23:50

   2. LFLex Fridman23:50

      Well, I have to ask then, uh, what do you think happened in Chernobyl? What lessons do we learn from Chernobyl nuclear disaster and maybe also Three Mile Island and, uh, Fukushima accidents? I think you're suggesting that it has to do with the humans a bit.

   3. DKDavid Kirtley24:02

      So with Chernobyl and Fukushima, I actually put Three Mile Island in a different category. In fact, um, some of the recent news in the last year is that we're gonna be restarting Three Mile Island because there's such a need for clean base load power. So that's, that's actually a very interesting other topic we should talk about is, is why and, and how we're doing that. But more than that, going back to the accidents that did happen, um, in both of those systems, you can point to the human failure rather than the engineering failures of those systems. That in Fukushima specifically there were multiple nuclear fission reactors on the same site that successfully kept running through the tsunami.... totally successfully, and were only later shut down for more political reasons. But the old one, the oldest of them that had been on site for, for long periods and maybe, maybe too long, I think some experts have looked at this in the past, um, was where the, some of the problems actually happened. And so, I look to that less as a, um, a failure of the engineering of the power plants, and more of the humans and around those systems, that if we, that we should be operating these plants as designed, and, and then I believe they're safe. And that gets to some of the atomic weapons questions that I think are the other part around nuclear reactors and fission reactors that are concerning for me.

   4. LFLex Fridman25:30

      Can you speak to those? So maybe this is a good place to also lay out the difference between nuclear fission power plants and nuclear fission weapons, and maybe also nuclear fusion power plants and nuclear fusion, uh, weapons. Like, what are the differences here?

   5. DKDavid Kirtley25:53

      Fusion power plants can't be used to make nuclear weapons. Fundamentally, that, th- the processes in fusion aren't the same processes that happen in nuclear bombs and nuclear weapons. And so it's actually one reason I s- started in fusion, and most of our team thinks about the mission of fusion, of delivering clean, safe electricity, is it also can't be used to make weapons. And I think that's a little bit of a distinction from traditional nuclear fission reactors, is that, while I totally believe as a nuclear engineer you can, you, we build power plants now that are safe, that aren't going to have reactions, they use a fuel, uranium and plutonium, that can be used to be made, to make nuclear weapons. That we know that if you take enough fissile material together, enough uranium and plutonium, put it in a small volume, that it will not just create a reaction, but it will create a super critical reaction that will then continue and grow and release a tremendous amount of energy all at once. And that is a bomb. That is a bad situation, and that is what we want to avoid. A lot of the key is recognizing that even though th- there are things called fusion bombs, the H-bomb, the hydrogen bomb, the hydrogen bomb has uranium in it. It's still a fission bomb. And so how this fundamentally works is that you have a fission reaction, a primary, and that creates radiation that induces a fusion reaction with a small amount of fusion fuel that then boosts that uranium reaction again. And so most of the energy, in fact, 90% of the energy in an H-bomb is all still from the uranium reactions themselves.

   6. LFLex Fridman27:37

      Yeah, I think people call it sort of the nuclear fusion bomb, hydrogen bomb, but really it's still a nuclear fission bomb. It's just that fusion is a part of the process to make it more powerful, but you still need, like you said, the uranium fuel. So it's not accurate to sort of think of it as a fusion bomb, really.

   7. DKDavid Kirtley27:53

      And if you take away that, that fissile material, that, that nuclear fission reaction, the fusion reaction doesn't happen at all. Um, in fact, there's been researchers that have, over the decades, tried to make an all-fusion bomb and been very unsuccessful at it. The physics and the engineering don't support it can ever happen with our understanding today. The topic we're talking about is more broadly called proliferation, and this is the creation of nuclear weapons in the world and the distribution of those weapons. And something we know as physicists and engineers is that fusion can't be used to make nuclear weapons. We know that. But that is not sort of widely known. And, and part of what we went out to do is work with the proliferation experts in the world, the people who work to prevent nuclear weapons from being made, being created, being shared throughout the world, because we know the challenges, the, the geopolitical challenges that happen. And we went to those proliferation experts, and we were worried they would have the, sort of the s- same historical question of, like, "Well, it's, the word nuclear is in fusion, so therefore it must be related." And, and in fact, the total opposite happened. What they told us is, "Please, please, go develop fusion power plants absolutely as fast as possible. The world needs this." And the proliferation experts were telling us that otherwise people would start enriching uranium throughout the world, and we'd be building enriched uranium power plants because we need the electricity that's clean and baseload. But in those processes, they'll be making fuel that could be one day used for atomic weapons, for nuclear weapons. And they were worried that, that, that the growth of this enriched uranium, think about the centrifuges, that having a lot more centrifuges happening all over the world would lead to more weapons, at least the possibility of it. And so they are pushing us as fast as possible, "Go build fusion generators and get them deployed everywhere." Not just in the United States, but all over the world, so that we're building fusion power and, and that's meeting humanity's needs, not this other thing. And so I was really pleasantly surprised. We've written a number of papers and worked with those communities, um, on this of, what does it mean? How is fusion power safe and can't be used for nuclear weapons?

6. 30:17 – 32:12

   Geopolitics

   1. DKDavid Kirtley30:17

   2. LFLex Fridman30:18

      So this might be interesting to ask on the geopolitics side of things. I have the chance to interview a few world leaders coming up. By way of advice, what questions should I ask world leaders to figure out the geopolitics of nuclear, nuclear proliferation-

   3. DKDavid Kirtley30:35

      Mm-hmm.

   4. LFLex Fridman30:35

      ... nuclear weapons, nuclear fission power plants, and nuclear fusion power plants? What's the in- interesting, intricate, uh, complexity there that you could, uh, maybe speak to?

   5. DKDavid Kirtley30:47

      The question I would want to ask is, what would you do...If we could deliver for you low cost clean industrial scale, tens or hundreds of megawatts of fusion power, that's low cost, clean base load, and doesn't have the geopolitical consequences of uranium and plutonium, of fissile material. What would you do there? How would that change your view of the next 30 years?

   6. LFLex Fridman31:17

      But also there's a lot of geopolitics connected to oil, natural gas-

   7. DKDavid Kirtley31:21

      Mm-hmm.

   8. LFLex Fridman31:21

      ... and other sources of energy, which I think are important in, uh, Saudi Arabia, in the Middle East, in Russia, um, I mean all across the world, and that's interesting too. So do you think actually if everybody has nuclear fusion power plants, that alleviates some of the geopolitical tension that have to do with energy, other energy sources?

   9. DKDavid Kirtley31:42

      I certainly do. That the fuel is in sea water all over. Everybody has deuterium.

   10. LFLex Fridman31:48

       (laughs)

   11. DKDavid Kirtley31:49

       Everybody has it.

   12. LFLex Fridman31:50

       (laughs) That's-

   13. DKDavid Kirtley31:50

       And so you can't have a monopoly on the fuel.

   14. LFLex Fridman31:53

       Yeah.

   15. DKDavid Kirtley31:53

       And no one can control the fuel and no one can turn off the fuel, no one can cut a pipeline, like that just cannot happen with fusion. And so if we can deploy those plants and we can deploy them quickly, then it- it decouples the ability of any one or any few countries to control energy.

7. 32:12 – 39:07

   Extreme scenarios

   1. DKDavid Kirtley32:12

   2. LFLex Fridman32:12

      Okay, so let's sort of return to the basic question. We already mentioned it a little bit, but is nuclear fusion safe? So the power plants that we're talking about, fusion power plants, uh, are they safe?

   3. DKDavid Kirtley32:26

      Yes. Fusion power is fundamentally safe. The physics and the reactions of the fusion system itself means you don't have runaways, and so we've talked about some of the human factors around power plants and plat- power systems and industrial scale systems, um, and that's something that we build into the design of these from today. Um, we look at, uh, how these systems might fail, and in fact some of the analysis we do is, um, we did this analysis for the Nuclear Regulatory Commission over the last few years looking at how do you regulate fusion power? As we're building the first fusion power plant, we need to make sure we're regulated safely, and so we spent a lot of time doing the technical case and the political case in the United States of how to regulate fusion. Um, and so the analysis we did is assume you have a fusion power plant that's operating, and then at any one time, a meteor strikes it. The whole thing is vaporized. What is the impact of that? So this is worse than you could ever imagine an actual physical scenario, but let's start there. Um, and the answer is you don't need to evacuate the populous nearby the fusion power plant. Um, and one of the keys I think that I come to when I think about this is the fuel, in that in a fusion generator, you are continuously fee- feeding in this hydrogen, these deuterium fuels, and at any one time in a helion fusion system, and most fusion systems, you have one second of fuel in that system. And so what that means is if you stop turning on ... If you stop putting fuel into that system, fusion just stops. But what it also means is that if something really catastrophic happened and uh- uh- for whatever reason, um, you have all that fuel that's not in the system, and fusion is so hard to make happen, you hit it with a meteor, you do anything, uh, in that nature, and fusion doesn't happen. That hydrogen, that heavy water, that deuterium just goes back into the environment safely and cleanly without- without issue. And so that's the fundamental safety mechanism of fusion, and you can compare that with other types of power plants, oil or a coal power plant. You might have a large pile of coal that then catches fire and burns, and it's not catastrophic, but you have a large coal fire for a long time releasing toxic fumes that you may have to deal with. Um, and in nuclear power, in a fission power plant, you may have several years of fuel sitting in the core, and in that case if something bad happened, you have all that potential energy, uh, for- for, uh, things to happen. But in fusion, you have literally one second of fuel at any time in the system, and having a tank of deuterium, which we have around all the time, can't do fusion by itself. It needs that complex system.

   4. LFLex Fridman35:17

      I love that there's like a PowerPoint going on in a secret meeting about like what happens if a meteor hits a- (laughs) a fusion power plant. Okay, so that's really interesting. Uh, what about the waste? What kind of waste is there for, uh, fusion power plants?

   5. DKDavid Kirtley35:31

      So the fusion reaction itself is still fundamentally an atomic reaction, and so during this reaction, you do create ionizing radiation. You create X-rays, you create neutrons, you create all these charged particles. Um, the charged particles themselves for a fusion reaction are all contained in the- the fusion system. Um, and the X-rays similar to, think about a dentist office, although a lot more than that, but that type of same X-ray and X-ray energy is absorbed by the fusion system. But the thing we do care about is those neutrons, and so we do have in a fusion system activation... We have during its- its operation, neutrons are made and leave, and so we have to shield these fusion systems during their operation. Um, and so this is very similar, and in fact, this is a lot of the work we did with the Nuclear Regulatory Commission over the last number of years, um, that there was a landmark agreement that happened for the NRC that then was codified into law last year called the ADVANCE Act, which is really powerful because it says for the very first time-... how the US government, leading the way on this, which I'm really proud of, will regulate fusion, and this gets into a little bit of the details, but the way the Nuclear Regulatory Commission regulates nuclear things in the United States is in these different sets of statutes. And nuclear reactors are regulated under something's- what's called Part 50, and there's a lot of variety of the regulatory language around that, but most of it is to handle special nuclear materials, uranium and plutonium. But fusion is not. Fusion is regulated under something called Part 30, and Part 30 is how hospitals are regulated, particle accelerators, other types of irradiators where as they're operating, you have very high energy particles, ionizing radiation, and you have to protect operators from it, and you have to shield them. And so we build concrete shields, and if you came and visited Helion, you would see p- uh, plastic, borated polyethylene, and concrete shielding, um, to protect operators and equipment from the fusion reactions while they're happening. Um, but again, you turn them off, and those fusion reactions stop, and that's really the key. Um, there's a funny, uh, story related to that. We, um, sto- we've been building fusion systems that do fusion a long time, and at- at some level we- they got powerful enough doing enough fusion, we started building these shields and- and shielding them like a particle accelerator. Um, and I went to the, uh, regulatory bodies that regulate Part 30, this is in Washington state, it's the Department of Health, and so I went to the Department of Health and said, "Here's an application for a fusion generator shielding permit, um, as- a- a- as a particle accelerator." And, um, uh, the very first question I got asked was, "Great, where do the patients go?" Because the standard form had a patient, uh, as a hospital, the patient dose for the particle accelerator, and then the shielding-

   6. LFLex Fridman38:26

      Mm-hmm.

   7. DKDavid Kirtley38:27

      ... and we talked all about the shielding and the operators, which is very similar for a Helion system. And we said, "No, no- no patients at all. No one's inside this thing. Our goal is to generate electricity one day." This was a lot of years ago. Um, and- and we were able to go through and work with the state agencies to license, uh, these fusion particle accelerators. We were th- as far as we know, the first licensed fusion system ever, um, a- as a particle accelerator for those first systems. Um, first license we had was in 2020. Um, we then have gone on and now license several of our fusion systems that we've built that do fusion, both the shielding as well as, um, some of the- the fuel processes.

8. 39:07 – 1:11:59

   How nuclear fusion works

   1. DKDavid Kirtley39:08

   2. LFLex Fridman39:08

      So high level, what are the- the different ways to build a nuclear fusion power plant? So can you explain what a tokamak is, what a stellarator is, and what's the linear approach that, uh, Helion is using?

   3. DKDavid Kirtley39:25

      So there are a number of ways to do fusion, um, and fundamentally in all fusion approaches, you're trying to do the same phys- same fundamental physical process, which is take these lightweight isotopes, heat them up so that they can, um, move at high velocity, over 100 million degrees, bring enough of them together, we call it density, enough of them together in a certain volume so that you have reactions happening, um, at a high rate, and keep them together long enough that they are able to collide into each other and do fusion and release energy. Um, that's the fundamental core. Now, how you do that, how you bring those particles together, how you hold them together long enough, there's a wide range of technologies that as humans we've been exploring, um, since the 1950s, and I think about several main categories. If you look at the fusion funding out there, government funding in the world, private funding actually has quite a different, uh, profile, which is an interesting thing to talk about. But in public funding, in federal funding in the United States, there's two mainline programs called inertial fusion and magnetic fusion, and in inertial fusion, what you're trying to do is bring together and push together by a variety of means, physical means, those particles. You push them together. The most common is called laser inertial fusion. Our colleagues at the National Ignition Facility did this really well and made world records in the last few years for being able to demonstrate you can do this and do it at scale, where you take very high power laser- lasers and pulse them together to combine them to do fusion for a pulse, for a very short period of time. Nanoseconds, billionths of a second. The other extreme, and you mentioned tokamaks and stellarators. Stellarators are actually my favorite-

   4. LFLex Fridman41:15

      (laughs)

   5. DKDavid Kirtley41:15

      ... so we'll- we'll talk about those. Graduate student in fusion, the stellarator is the first thing you learn about.

   6. LFLex Fridman41:21

      Mm-hmm.

   7. DKDavid Kirtley41:21

      Because there's a mathematical solution for a stellarator that solves perfectly.

   8. LFLex Fridman41:26

      Mm-hmm.

   9. DKDavid Kirtley41:27

      And- and, um, and- and you can write it out and you can solve it and analytically it's very simple. Building one is very hard, and so it's taken, uh, uh, humanity a n- uh, a number of decades to be able to build stellarators and we can do it now, um, with the Windenstein 7-X that came online, uh, in the last few years being the premier, uh, stellarator in the world.

   10. LFLex Fridman41:49

       I should say, all the different ways to do fusion all just look so badass in terms of engineering, creating this containment, extremely high temperature, high density, everything's moving super fast, everything is happening super fast. It's just fascinating that humans are able to do... Like there's certain things, accelerators are that a little bit, but this is even cooler because you're generating energy that can power humanity with this machine. Anyway, can you just speak a little bit more to the inertial and the magnetic fusion systems?

   11. DKDavid Kirtley42:23

       In a magnetic system, your goal is not to push together those particles as fast as possible. Your goal is to hold onto them for as long as possible, and to do that we use magnetic fields. So let's take a step back. What is a magnetic field? Uh-So in an electromagnet, um, there's a variety of ways to make a magnetic field. One of the most famous I think everyone is familiar with is Earth itself. Earth has what we call the magnetosphere, which is the magnetic protection that's generated actually by the core of the Earth. But we have a magnetic field around the Earth, and that magnetic field protects us from particles coming from the galaxy, galactic cosmic rays and solar particles that would come to Earth. That magnetic field, when you run a compass, you see the magnetic field from the Earth. So we know it's happening. It's all over. But how we generate it with electric currents is a little bit different. And what we do is that we have a loop of, of wire, and the simplest way to think about it is literally a round loop. And in that loop, you have electrons. You have electrical current that's running. And when electrical current, this is some of Maxwell's equations that we discovered in the 1800s, that when you have an electrical current in a wire, it generates a magnetic field inside that wire. And so when you look at fusion systems, uh, you always have these big magnetic coils with large amounts of current. We don't run a little bit of current. In our systems, we have hundreds of mega amps of current. If you think about at your house, you have your, um, uh, breaker box with 200 amps or maybe a 400 amp breaker box, and we run 100 million amps of electrical current. So massive amounts of electrical current to be able to do this. Um, so that magnetic field that's generated inside that magnetic coil has some really special properties, and, and we take advantage of those properties to do fusion. And some of those properties are not intuitive. So here's, here's one of my favorites. When you have an electromagnetic field, you have this coil with electricity going around it and you have a magnetic field inside of it, and then you have a test particle, a charged particle, an electron or an ion, which is if you imagine to generate this, I have a coil with electrons moving around it. But if I put one in the middle of it, in this magnetic field, some really interesting things happen. That electron or that ion, that charged particle is what's called magnetized. And what magnetized means is that it's trapped on that field line. In fact, even really more interesting is that it oscillates around that field line. And so the way I think about this is if you think about the Earth's magnetosphere again, and you think about the charged particles, the aurora, the, the northern lights is a charged particle trapped in the Earth's magnetic field going around the Earth's magnetic field. And in the same way, in fusion, we do the same thing here on Earth, but in a smaller direction where we trap these particles on magnetic fields and they can go around and stay trapped to that magnetic field line.

   12. LFLex Fridman45:29

       How much of the physics at this scale is understood here? Like, how these systems behave when you, when you, when you, um, attract a magnetic field in this way? Like, is this fundamentally now an engineering problem, or is there a new physics to be discovered about how the system is behaving?

   13. DKDavid Kirtley45:48

       In, in fusion, the physics we are using is actually quite old, that the fundamental electromagnetic physics is 1800s physics. The fundamental atomic physics is early 1900s. And so the fundamental physics of how these work is very well understood. Putting them all together into a power plant, that's hard. And so you can do the math, you can do the math. Every, uh, introductory grad student does the math on a stellarator and say, "This is all I need to do. Um, I just need to make a magnet- a magnetic coil in this very complicated shape." And then fusion will happen. Um, however, doing that in practice is actually quite, quite challenging.

   14. LFLex Fridman46:27

       So maybe you could speak a little bit more. So the, the stellarator and the tokamak, what's the difference between those two? They're both magnetic fusion systems? And then what does Helion do?

   15. DKDavid Kirtley46:38

       The tokamak and the stellarator are both magnetic systems. Their goal is to generate this magnetic field and hold onto the fusion fuel long enough. Like I mentioned, these charged particles are trapped on the magnetic field. In fact, they're oscillating. We call that a gyro orbit, is the radius that they oscillate around this magnetic field. Um, and we're, we've been talking about atomic physics, where everything is, uh, at this nano scale. But gyro orbits are not. Gyro orbits for these fusion particles are measured in inches, and so th- they're, they're in on a scale that, that, that we can see and measure and, and understand really intuitively. Um, and in a magnetic system, your goal is to simply trap as many of these particles as you can for long enough that... and heat them so they're hot enough so that they bang into each other. They collide enough that you're doing fusion, and you're doing enough fusion to overcome as fast as you're losing those particles. And so that's what, what happens when you put particles in a magnetic field and you try to hold onto it. The challenge is that's really hard to hold on to them long enough. These particles are moving around. They're moving at very high velocity, millions of miles per hour. They're colliding with each other, and they're getting knocked off and getting knocked away. So we've talked about inertial fusion, where you try to confine a, a fusion plasma by crushing it as fast as possible, and magnetic fusion, where you just simply have a magnetic field and your goal is to hold onto it for as long as possible. But there's another way to do fusion, and in some ways, it's one of the earliest approaches for fusion that was successful. Um, as scientists and engineers, maybe we're not too creative with the terminology. We call the technique that Helion uses magneto-inertial fusion because it does a little bit of both. So to understand that, we can actually go back in history a little bit and think about the evolution of some of these approaches to fusion.And so from our perspective, we look at the technology that we use as built on physics experiments that were very successful in the 1950s. Um, and in those systems, the earliest pioneers of fusion said, "I know we n- understand the physics. We have to take these gases, heat them to 100 million degrees, and then confine them, push them together so that fusion happens." And so, what is the best way to do that? So the, some of the earliest programs we call them theta pinch. And what those programs were, were a linear topology, because we knew how to build these magnets. Uh, it's called a solenoid, where you take a, a series of electric coils, you run electrical current through them that generates a magnetic field. Great. So you have a magnetic field. Now you add your fusion particles. Okay? So you've added fusion particles to this solenoid. Here's the challenge. Those particles, as they're sitting in that magnetic field, in this nice magnet, escape. They leave out the ends, because there's nothing holding them in. Great. So that makes sense. Um, and so that doesn't work. Okay? So then the next approach is say, well, one, one branch of fusion said, "Okay, well, to solve that, why don't we take this solenoid and bend it around? Let's just make it a big donut. So as they're escaping, they go around and around in a circle." Great. That's a great approach. And so one branch of fusion went down that direction. And, and that became, that evolved into the stellarator and the tokamak. Different ways of taking those solenoids and wrapping them around, so that the plasmas go round and round in that magnetic field and are ho- those charged particles are held long enough that fusion happens. But there's a different way to do it. And so the theta pinch was what was born in the 1950s of take this magnetic field and, oh, they're trying to escape. Great. Let's not let them escape. Let's close the bottle.

   16. NANarrator50:20

       Mm-hmm.

   17. DKDavid Kirtley50:20

       Let's close the ends. And so we make the magnetic field much stronger at the ends. This one was called the mirror. And so the idea was that the, the particles would bounce in between. And that worked, and they got hotter and hotter and hotter. But guess what? As you kind of would imagine, as this mirror topology, this linear topology, the pressure increased inside, the, the particle pressure, the, the particles tried to push back on the magnetic field. They were trying to escape now. They're trying, they're getting hotter and hotter and just as you imagine hot gas in a balloon tries to get out the ends, as you could not hold it tight enough at the ends to keep those particles in. And in fact, the problem is the hottest ones were the ones that would escape.

   18. NANarrator50:59

       Mm-hmm.

   19. DKDavid Kirtley51:00

       And so you do a good job of heating it, and they'd all leave out the ends. Okay? So then the next iteration has said, "Okay, well, why don't we just not try to hold on to it very long? Why don't we squeeze it?" And so rather than just holding it constantly, let's now crush it. So we built this solenoid, we pinched the ends, and then we crushed it. And when, what I mean by crushing it is not actually, like, crushing any magnets or changing the w- the, the topology or, or moving any parts, but just rapidly increasing the magnetic field. And so going from a magnetic field that's just holding it to now taking all those particles, if you imagine they were in a, a, uh, streaming around together and then rapidly increasing the magnetic field, so that those particles get closer and closer and closer together. So you increase the density.

   20. NANarrator51:47

       Mm-hmm.

   21. DKDavid Kirtley51:47

       And now fusion starts to really happen. But they ended up hitting a technological limit. So this is the part that, that, um, I look back and, um, I look at the pioneers that, in 1958, there was some pioneering work done, um, and this was in California, what later became Livermore Labs. There was also some work done, uh, at other national labs too, these were all federally funded programs, to explore this, uh, theta pinch topology of can you just squeeze the plasma down fast enough, hard enough? This was 1958. The transistor was sitting in the laboratory. And they were commuting, they were turning on millions of amps of electrical current. And they were doing it, we haven't talked about the time scales, but they were doing it in, uh, millionths of a second. Microseconds, megahertz speeds. Um, and this was in 1958. No transistor, no CPUs, and, um, and no electrical switches, none of the things that I take for granted every day. And so they were able to show, at that time, the highest performing fusion systems. Um, they got to temperatures, they didn't get to 100 million degrees. Not quite then. But they got to 50 million degrees. They were outperforming everything else in fusion, but they reached a technical limit where they just could not build it any more. And so, they, the, those pioneers went in a different direction and they started down the laser inertial path of saying like, "Okay, well, we can't do these, uh, electromagnetic pinches, but we now have inv- this new thing has invented the laser, which turns on in a nanosecond. It's fast, it's interesting. Let's go down that path." Um, and it's not, you have to fast-forward a couple of decades to researchers found with some of these theta pinches when they're operated in a very specific way, something else happened, something new happened. And that these plasmas where before they squeezed them very hard, and just like squeezing a tube of toothpaste, they squirted out the ends. Now it didn't squirt out the ends. It actually pushed back. It stayed confined. It stayed trapped inside that linear topology. Even though the ends were open, the plasma didn't leave. And so there was a large amount of programs of, like, "What is happening here? This is an accidental discovery in plasma physics that something new is happening." And what we discovered is we now call the field-reversed configuration. Uh, there's numerous programs of FRC, field-reversed configuration programs, um, both at national labs, there's actually a number of private companies now of people building field-reversed configurations. Um, and they have some really unique properties, but fundamentally, talking about the main difference, I described the solenoid with magnetic fields throughout the center of that volume and plasma trapped-... going back and forth. But some other things can happen, which is really interesting. And what they discovered early is if they have field going in one direction, so the plasma, the, uh, electrical current is going around the loop and the plasma is going back and forth along this magnetic field line inside that solenoid, inside that theta punch. But then they changed the direction of the magnetic field, and this is what we call field reversal. And this is really the key, is that you start with the plasma going in one direction, and then very rapidly, you change the direction. You change the direction and reverse the direction of that field. And something really interesting happens, which is the plasma, this fu- this ch- fusion fuel, these charged particles which are trapped on the magnetic field lines, um, that are moving back and forth, you change the direction. What that means is that they're- you're trying to take that electrical current and that magnetic field and reverts its direction, flip it. And but it can't flip fast enough, that the plasma is sitting there and you can't move the particles. And so what's really interesting is what happens is that because the particles can't move but you've now flipped the direction of the magnetic field, you've, you've inverted it, something really, really unique happens, which is that the plasma itself con- reconnects internally. And so now what you're left with is an outside magnetic field, an electrical coil, and inside, the plasma, where now it was m- before it was moving along, it's now moving internally.

   22. LFLex Fridman56:06

       Rapidly reversing the magnetic field, plasma self-organizes into a closed field.

   23. DKDavid Kirtley56:12

       Mm-hmm.

   24. LFLex Fridman56:14

       W- what? (laughs)

   25. DKDavid Kirtley56:15

       Yup.

   26. LFLex Fridman56:15

       So how-

   27. DKDavid Kirtley56:16

       It soun- it sounds wild.

   28. LFLex Fridman56:17

       It's, it's, it's- yeah. It's so- so first of all, there's a lot of- there's a million questions I have.

   29. DKDavid Kirtley56:21

       Mm-hmm.

   30. LFLex Fridman56:22

       So one of them, what's rapidly? What time scale are we talking about here?
9. 1:11:59 – 1:17:00

   Extreme temperatures

   1. DKDavid Kirtley1:11:59

      the whole time.

   2. LFLex Fridman1:12:00

      So you're trying to reach 100 million degrees. How do you get to that temperature fast? And by the way, what can you say to help somebody like me understand what 100 million degrees is like? It seems insane. What does that world look like? I guess just everything's moving really fast. Uh, like you said, you can't put anything mechanical in there.

   3. DKDavid Kirtley1:12:21

      Yeah. So a couple of key things happen. So when gas is that hot, there's a... We talk about the states of matter. You have solids where ice, it's cold, the atoms are now bound in a lattice structure together. They're held together. And then liquid, you've broken a lot of that lattice structure. They can move around. They have some kinetic energy, but they're still pretty contained. They stay in the bowl. Keep heating it, now you're in gas, and now these particles are free to move around. They're moving around. They're bouncing off of each other all the time, and you can keep heating it from there, and that's where we talk about, um, some more phases of matter. Um, we can add a little bit more physics here. Uh, we talk about rarefied gases.So when we think about most gases that, that humans interact with, they act like a fluid. And what I mean by that is that they're colliding with each other so often that the particles at any one place... Here, the air is roughly the same temperature as the air here. That these particles are bouncing off of each other. So if you put a really hot one right here, it would then cool enough that all the air is roughly on the same temperature. Um, but you can be what is called rarefied, and this is like space. This is where now you have particles moving around, but they don't collide with each other very often, and so you can have one very, very high energy particle and very cold energy particle, and they may not even touch each other, but maybe occasionally they bang into each other or they collide, and then they transfer energy. And that's where we call rarefied. And then you can go even hotter than that, and that's where now the actual atomic states which has, uh, the nucleus, which is a proton and a neutron and an electron, gets so hot that electron gets energized and then escapes, leaves the system. Um, and now they're charged. We have a positive nucleus and a negative electron floating out. And that happens on the order of 10,000 degrees. So way hotter than what we're used to. But now we're gonna go hotter. We're gonna take this plasma and go even hotter. And what does that mean? At that point, a lot of the way we think about temperature doesn't really apply, the idea that you have these random motion of particles, because now they're all individual particles moving at very high velocities. So what it's really is a, is a, is a, a, a measurement of, is velocity. It's really a measurement of how fast is that particle moving. Um, and, and that's how I really think about temperature when you get to that 100 million degrees. And so it does r- s- it does some more complex things. If you have this high energy particle, that's why we like fusion, is moving at high velocity and there's another one moving at high velocity, they will come together, they will collide, and they will fuse. But other things will happen. You don't want to touch that high velocity particle with any kind of material, 'cause it will collide with that material, damage that material, and usually, like, blow off some chunks of that material. So we don't do that. We keep those charged particles in a magnetic field. So they just bounce around, and they don't ever touch anything. And that, that's, that's really important. Um, and so it's, it's less thinking about it from the way we normally think about hot and cold, and more thinking about it from a v- velocity point of view.

   4. LFLex Fridman1:15:20

      So what we should be imagining is, uh, extremely fast moving, what is it, one million miles per hour? Is that accurate?

   5. DKDavid Kirtley1:15:29

      That's the right kind of order for these systems.

   6. LFLex Fridman1:15:32

      Crazy. And so you're looking for them to collide. Well, first of all, to get back, is there some interesting insights, tricks, anything you could say to the complexity of the problem of getting it to that high temperature quickly?

   7. DKDavid Kirtley1:15:46

      So if temperature is velocity, that means they're moving quickly over a given amount of space. Speed is distance divided by time. And so, um, if you have a s- a machine of a certain size and it's moving very fast, that tells you the time that that particle is moving from place to place in that machine. Um, and, in fact, if it's a million miles per hour, these are on the order of 100 kilometers per second, which you can flip that around and you can say you're moving at meters per microsecond.

   8. LFLex Fridman1:16:19

      Mm-hmm.

   9. DKDavid Kirtley1:16:19

      So feet per millionth of a second.

   10. LFLex Fridman1:16:21

       (laughs)

   11. DKDavid Kirtley1:16:22

       And so that fundamentally tells you, and we've known this, as soon as you say, "I wanna do fusion," you know you need to react to the universe in microseconds and, and be able to understand the system in that speed. And if you get it hotter, it goes even faster, and you have to go faster. And so we look at those, and that's how we think about the systems. We measure everything in microseconds, not in seconds. And so when you do fusion, it's pretty wild, it's literally a flash. Pshh. Fusion happens-

   12. LFLex Fridman1:16:50

       Mm-hmm.

   13. DKDavid Kirtley1:16:50

       ... and it's over. You start it, you do a lot of fusion, you recover energy from it, and then you turn it off before the human eye can really respond

10. 1:17:00 – 1:28:54

    Fusion control and simulation

    1. DKDavid Kirtley1:17:00

       even.

    2. LFLex Fridman1:17:00

       And there's a computer managing all this. Like, how do you even program these kinds of systems to do the switching? Is there some innovation required there?

    3. DKDavid Kirtley1:17:09

       So I'm continuously amazed by what the pioneers in fusion were able to do before the computer existed, 'cause they had to control things at this scale. But maybe it was pretty hard and, and, and why we've been able to be, take what they did and build on it, because now we use modern gigahertz scale computing to be able to do this. And so even when I started my career, we talked about like megahertz processors. Um, megahertz is microseconds. That's great. You're kind of at the border of fast enough, but you can't do computation at that speed if, if all it can do is respond in one microsecond. But now gigahertz means I can do a thousand operations in that one microsecond, so I can do more useful things. So we use mostly... This is way too fast for any human to respond to. So we use what's called programmable logic. So we program in sequences to the fusion system to be able to do this reversal. We pre-program it, and then we run a sequence, and then fusion happens. Um, and so in this sequence, uh, programming language, we use a variety of them. Some of the fusion codes are actually written in Fortran still.

    4. LFLex Fridman1:18:17

       Nice.

    5. DKDavid Kirtley1:18:18

       And though a lot is now more and more run in Python. And so we do a lot of Python. We do some Java, and then we also have, uh, because of the speed of this, it's a lot of assembly language programming. So we go right to the assembly level of the programmable logic FPGAs, and we program those. And so to be able to run one of these systems, we typically have a series of electrical switches that turn on this electrical current. Those are controlled viv- via fiber optic because the wires are just too slow. And so fiber optic I can respond, I can send photons at the speed of light, and so those fiber optics can respond in nanoseconds. And then I trigger those fiber optics with programmable logic that we've programmed in the hard asse- hardware assembly language.

    6. LFLex Fridman1:19:00

       As a small tangent, let me do a, uh...... a call to action out there. I'm still looking for the best Fortran programmer in the world if people, uh, to talk to them, 'cause so many of the essential systems the world runs on is still programmed in Fortran. I think it's a fascinating programming language. Cobalt too, but Fortran even more so. It's one of the great sort of co- computational numerical programming languages. Uh, anyway, what, uh ... In terms of the sensors that are giving you some kind of information about the system, in terms of the diagnostics, like what kind of, at this time scale-

    7. DKDavid Kirtley1:19:40

       Mm-hmm.

    8. LFLex Fridman1:19:41

       ... what can you collect about the system such that you can respond at the similar time scale?

    9. DKDavid Kirtley1:19:49

       So I'm also calling out for Fortran programmers. So- (laughs)

    10. LFLex Fridman1:19:53

        (laughs)

    11. DKDavid Kirtley1:19:53

        For different reasons, but yes. Great. The diagnostic systems is really one of the keys to how we do this effectively, because you need to be able to tell the system, "We're gonna trigger electrical current and we're gonna do it in a microsecond. And we need to know if it's working right." And so in one of these FRC or these pulsed magnetic systems, you won't have just one electrical switch. I mentioned 100 mega amps, 100 million amps of electrical current. Each ... Even the big transistors we use can only run at 30,000 amps. So you'll end up with tens of thousands, in fact the systems we build now, tens of thousands of parallel electrical switches all operating in harmony together. And so you need to be able to bui- build a system, and this is what we spend, uh, a lot of time with, and I made the joke that in a lot of ways Helion's an electrical engineering company, to be able to con- both program, control, and then detect how they're operating, and do it all very fast. Um, so in a typical sequence, we will pre-program, the operators will pre-program a sequence, um, usually fed from a, a numerical simulation of expecting how the fusion system will perform. We start with a calc- a, a set of calculations. We then pre-program all of these electrical switches to a certain sequence to be able to inject the fuel, reverse it, and then compress it up to fusion conditions. And then we trigger that, and then l- and then let it go, and, and, and measure fusion happening. Um, but during that process, have to be real time recording and, and measuring all of the semiconductors and all of the switching in the system. I'm not even gonna talk about measuring fusion diagnostics. That's a whole nother thing which we can talk about. This is just on the electrical c- control side. Um, and so some of the pioneering things we've been able to do is that real time you are monitoring all of these switches. You're watching who is triggering correctly, who is not triggering cor- correctly! And if systems aren't working, you're shutting down this, 'cause you wanna make sure that all the sequences are, are, are operating correctly. So some of the key diagnostics, it's actually pretty amazing that even early in my career we didn't have a lot of fiber optics built into the system. And now it's absolutely essential. And so every one of these electrical switches has fiber optic signals going into it, and fiber optic signals coming out, understanding how it's actually operating. Um, and real time, all of these systems are being monitored by more fiber optics. Um, we call these Rogowski coils, but they're electromagnetic coils that are powered by the electrical current themselves. So as the switches are conducting, they broadcast a signal that says, "Yes, I'm electrically conducting an optical signal," fiber optics that come back to a central repository where we detect those signals. Um, and so real time we're monitoring all of this so that we know that these systems are behaving and operating at their, their optimal performance.

    12. LFLex Fridman1:22:48

        What's the role of numerical simulation in all of this? Sort of, I guess ahead of time, uh, how much numerical simulation are you doing to understand how the system is going to behave, how the different parameters all come together, uh, the electrical system and how that all maps to the, the, the fusion that's actually generated?

    13. DKDavid Kirtley1:23:12

        Yeah. The operation of a fusion system is, is pretty fascinating, because all of this happens on a time scale where human operators cannot be in-

    14. LFLex Fridman1:23:19

        Mm-hmm.

    15. DKDavid Kirtley1:23:19

        ... cannot really be involved. Um, and so, uh, you have to have pre-programmed m- the majority, we call them shots. You're gonna do a shot. And when you're operating them repetitively and you're running long periods of times, you still have all computers doing both the triggering and the op- and the measuring of, of how they're performing real time, the whole time. Um, and so, um, how this typically works, at least in our systems, is that we will design a system with a combination of with, with some nu- numerical simulation tools that we, we've developed based off of decades and decades of amazing government programs. National, uh, programs developed these numerical codes. Um, we use a kind of a code called an MHD, magnetohydrodynamic code. Um, and that's, uh, for people, for the engineers out there, um, who are used to CFD, computational fluid dynamics, this is very similar, where you take the same sets of equations actually and add the electromagnetic equations on top of those. And so you get magnetohydrodynamic.

    16. LFLex Fridman1:24:23

        Are you simulating at the level of a particle? Is there some qua- quantum mechanical aspects to this also? Does the ... How low does it go?

    17. DKDavid Kirtley1:24:30

        Yeah. We have multiple codes at different levels, um, because one of the, the main computational challenges is, um, amazingly even given all that we are, have been b- have built for fusion systems, computers are still not fast enough to measure, to simulate everything. Um, and so we have, uh, a number of codes that we use. Um, one we call fluid codes, where you treat the ions, the electrons, all these fusion particles, you treat them as, as fluids, as gases-

Episode duration: 2:36:54