Dennis Whyte: Nuclear Fusion and the Future of Energy | Lex Fridman Podcast #353

1. 0:00 – 0:32

   Introduction

   1. DWDennis Whyte0:00

      Why weren't we pushing towards economic fusion, and new materials, and new methods of heat extraction, and so forth? Because everybody knew fusion was 40 years away. And now it's four years away.

   2. LFLex Fridman0:13

      The following is a conversation with Dennis White, nuclear physicist at MIT and the director of the MIT Plasma Science and Fusion Center. This is the Lex Fridman podcast. To support it, please check out our sponsors in the description. And now, dear friends, here's Dennis White.

2. 0:32 – 18:31

   Nuclear fusion

   1. LFLex Fridman0:32

      Let's start with the big question, what is nuclear fusion?

   2. DWDennis Whyte0:35

      It's the underlying process that powers the universe. So, as the name implies, it fuses together or brings together two different elements, technically nuclei, that come together. And if you can push them together close enough that you can trigger essentially a, a reaction, what happens is that the, the element typically changes. So, this means that you change from one element to another, chemical element to another. Underlying what this means is that you change the nuclear structure. This rearrangement, through E equals MC squared, releases large amounts of energy. So, fusion is the fusing together of lighter elements into heavier elements. And when you go through it, you say, "Oh, look. So, here are the initial elements, typically hydrogen, and they had a particular mass, rest mass." Which means just the mass with a, with no kinetic energy. And when you look at the product afterwards, it has less rest mass. And so you go, "Well, how is that possible? Because you have to keep mass." But mass and energy are the same thing, which, which is what E equals MC squared means. And the, the conversion of this comes into kinetic energy, namely energy that you can use in some way. Um, and that's what happens in the center of stars. So, fusion is literally the reason life is, is viable in the universe.

   3. LFLex Fridman1:57

      So, fusion is happening in our sun. And what are the elements?

   4. DWDennis Whyte2:01

      The elements are hydrogen that are coming together. Um, it goes through a process, which is probably gets a little bit too detailed. But there's, it's, it's, it's a somewhat complex catalyzed process that happens in the center of stars. Um, but in the end, stars are big balls of hydrogen, which is the lightest, it's the simplest element, the lightest element, the most abundant element. Most of the universe is hydrogen. Um, and it's essentially a sequence through which these processes occur that you end up with helium. So, those are the primary things. And the reason for this is because helium has, uh, features as a nucleus, like the interior part of, of the atom, that is extremely stable. And the reason for this is helium has two protons and two neutrons. These are the things that make up nuclei that make up all of us, along with electrons. And because it has two pairs, it's extremely stable. And for this reason, it, when you convert the hydrogen into helium, it just wants to stay helium, and it wants to release, uh, kinetic energy. So, stars are basically conversion engines of hydrogen into helium. And, uh, I mean, this also tells you why you love fusion. I mean, 'cause our, our sun will last, you know, 10 billion years appro- approximately. Uh, that, that's how long the fuel will last.

   5. LFLex Fridman3:23

      But to do that kind of conversion, you have to have extremely high temperatures.

   6. DWDennis Whyte3:26

      It is one of the criteria for doing this, but it's the easiest one to understand. And why is this? It's because effectively what this requires is that these hydrogen, uh, ions or, which is really the bare nucleus, so they have a positive charge. Everything has a positive charge of those ones. Is that to get them to, to trigger this reaction, they must approach within distances which are like the size of the nucleus itself, because the nature... In fact, what it's really using is something called the strong nuclear force. There's four fundamental forces in the universe. This is the, the strongest one, but it has a strange property is that it, while it's the strongest force by far, it only has impact over distances which are the size of a nucleus. So, to get, let's put that into, what does that mean? It's a millionth of a billionth of a meter, okay? Incredibly small distances. But because the distances are small and the particles have charge, they want to push strongly apart. Namely, they have repulsion that wants to push them apart. So, it turns, when, when you go through the math of this, the average velocity or energy of the particles must be very high to have any significant probability of the reactions happening. And so the center of our sun is at about 20 million degrees Celsius. Um, and on Earth, this means, it's one of the first things we teach, you know, entering graduate students, you can do a quick, uh, you can do a quick, uh, basically power balance, and you can, you can determine that on Earth, it, it requires a minimum temperature of about 50 million degrees Celsius on Earth.

   7. LFLex Fridman5:02

      To perform fusion?

   8. DWDennis Whyte5:03

      To get enough fusion, uh, that you would be able to make, uh, get energy gain out of it. So, you can trigger fusion reactions at lower energy, but they, they become almost vanishingly small at lower temperatures than that.

   9. LFLex Fridman5:18

      First of all, let me just linger on some crazy ideas. So-

   10. DWDennis Whyte5:20

       Yeah.

   11. LFLex Fridman5:21

       Uh, one, the strong force, just stepping out and looking at all of physics, is it weird to you that there's these forces, and they're very particular? Like, it operates at a very small distance, and then gravity operates at a very large distance, and, and they're all very specific. And the standard model describes, uh, three of those forces extremely well, and there's-

   12. DWDennis Whyte5:42

       And this is one of them, and- (laughs)

   13. LFLex Fridman5:43

       Yeah, this is one of them.

   14. DWDennis Whyte5:44

       Yeah.

   15. LFLex Fridman5:44

       And it just all kind of works out.

   16. DWDennis Whyte5:46

       Yeah.

   17. LFLex Fridman5:46

       There's a, a big part of you that's, uh, you know, an engineer. So, do you stu- step back and almost look at the philosophy of physics?

   18. DWDennis Whyte5:55

       So, it's interesting 'cause as, as a scientist, I see the universe through that lens of essentially the interesting things that we do are through the forces that are, get used around those. And everything works because of that.... Richard Feynman had a, a... I don't know if you've ever read Richard Feynman. It's a little bit o- of a tangent, but-

   19. LFLex Fridman6:12

       He's never been on the podcast.

   20. DWDennis Whyte6:13

       He's never been on the podcast.

   21. LFLex Fridman6:14

       Yeah.

   22. DWDennis Whyte6:14

       He was, unfortunately passed away, but one of, like a, a, like a hero to almost all, all physicists.

   23. LFLex Fridman6:19

       Yeah.

   24. DWDennis Whyte6:19

       And then part of it was because of what you said. He kind of looked through a different lens at these what are, typically look like very dry, like equations and relationships, and he kind of s- I think he brought out the wonder of it in some sense, right, for, for those. He posited what would be, if you could write down a single, not even really a sentence but a s- a single concept that was the most important thing scientifically that we, that we knew about that, in other words, you had only one thing that you could transmit to like a future or past generation. It was very interesting. It was, um... So it's not what you think. It wasn't like, oh, strong nuclear force or-

   25. LFLex Fridman6:56

       (laughs) Yeah.

   26. DWDennis Whyte6:56

       ... fusion or something like this. And it's very profound, which was he was, that the reason that matter operates the way that it does is because all matter is made up of individual particles that interact each other through forces. That was it.

   27. LFLex Fridman7:13

       So just-

   28. DWDennis Whyte7:14

       The atomic theory basically. Yeah.

   29. LFLex Fridman7:16

       Yeah.

   30. DWDennis Whyte7:16

       Which is like, wow, that's like so simple, but it's not so simple. It's because, like w- who thinks about atoms, that they're made out of? Like I, I... This is a good, this is a good question I give to my students. How many atoms are in your body? Like almost no student's gonna answer this. But to me that's like a fundamental thing.
3. 18:31 – 32:58

   e=mc^2

   1. LFLex Fridman18:31

      E equals MC squared, you mentioned. How amazing is that to you, that energy and mass are the same?

   2. DWDennis Whyte18:35

      Yeah.

   3. LFLex Fridman18:36

      And what does that have to do with nuclear fusion?

   4. DWDennis Whyte18:39

      So, it has to do with everything we do. It's the fact that energy and mass are equivalent to each other. They're just, the way th- th- we usually comment to it is that they're just energy, just in different forms.

   5. LFLex Fridman18:49

      Can you intuitively understand that?

   6. DWDennis Whyte18:52

      Yes.

   7. LFLex Fridman18:53

      (laughs)

   8. DWDennis Whyte18:53

      But it takes a long time. (laughs) I (laughs) um ha- haven't for a while, but usually, uh, often I've, I- I teach the, um, uh, the inter- introductory class for incoming nuclear engineers, and, and so we put this up as an equation, and we go through many, um, iterations of, of using this, uh, to, to, how- how you derive it, how you use it and so forth. And then u- usually in the final exam, I would give, uh, I would basically take all the equations that I've used before and I flip it around. I basically, instead of thinking about energy as equal to, to mass, it's sort of mass is equal to energy. And I ask the question a different way, and usually about half the students don't get it. It takes a while i- t- to get that intuition. Yeah. Um, so, so in the end, it's interesting is that th- this is a- is actually the source of all free energy because that energy that we're talking about is kinetic energy if it can be transformed from mass. So, it turns out even, even though we, we used E equals MC squared, this is burning coal and, and burning gas, or/and burning wood is actually still E equals MC squared. The problem is that you would never know this because the relative change in the mass is incredibly small. By the way, which comes back to fusion, is which is that E equals MC squared. Okay, so what does this mean? It tells you that the r- the amount of energy that is liberated in a particular reaction when you change mass has to d- because C squared is, that's the speed of light squared.

   9. LFLex Fridman20:19

      It's a large number.

   10. DWDennis Whyte20:19

       It's a very large number, and it's totally constant everywhere in the universe, which is the-

   11. LFLex Fridman20:23

       Which is another weird thing.

   12. DWDennis Whyte20:24

       Which is another weird thing, and in all rest frames and th- actually, the relativity stuff gets more (laughs) difficult conceptually un- until you get through. Anyway, so you go th- you g- you go to that and, and it's, and what that tells you is that it's the relative, it's the relative change in the mass will tell you about the relative amount of energy that's liberated. And this is what makes fusion, and you asked about fission as well too, this is what makes them extraordinary is because the relative change in the mass is very large as compared to what you get, like, in a chemical reaction. In fact, it's about, it's about 10 million times larger. And that is at the heart of why you use something like fusion. It's because that is a fundamental of nature. Like, you can't beat that. So, uh, whatever you do, if you're thinking about l- and why do I care about this? Well, 'cause mass is, like, the fuel, right? So, this means gathering the resources that it takes to gather a fuel, to hold it together, to deal with it, th- the environmental impact it would have. And fusion will always have 20 million times the amount of energy released per reaction that you could those. So, this is why, you know, we consider it the ultimate, like, environmentally friendly energy source is because of that.

   13. LFLex Fridman21:40

       So, is it, is it correct to think of mass broadly as a kind of storage of energy?

   14. DWDennis Whyte21:46

       Yes.

   15. LFLex Fridman21:47

       You mentioned it's environmentally friendly. So, nuclear fusion is a source of energy. It's cheap, clean, safe, so easy access to fuel and virtually unlimited supply, no production of greenhouse gases, little radioactive waste produced allegedly.

   16. DWDennis Whyte22:03

       Mm-hmm.

   17. LFLex Fridman22:03

       Uh, can, can you sort of elaborate why it's cheap, clean, and safe?

   18. DWDennis Whyte22:07

       I'll start with the easiest one, cheap. It is not cheap yet because it hasn't been made at a commercial scale.

   19. LFLex Fridman22:14

       Time flies when you're having fun but yes.

   20. DWDennis Whyte22:15

       It d- yeah, yeah. (laughs)

   21. LFLex Fridman22:18

       But yes, not yet.

   22. DWDennis Whyte22:19

       Yeah, but-

   23. LFLex Fridman22:19

       We'll talk about-

   24. DWDennis Whyte22:20

       And actually, we'll- we'll- we'll- we'll come back to that because it- it- it- this is cheaper, m- or, or a more technically correct term that it's econom- that it's economically interesting is, is really the primary challenge actually of, of fusion at this point. Um, but I think we can get back to that. So, what were the other ones? You said, um-

   25. LFLex Fridman22:38

       So, so cheap, we're ta-

   26. DWDennis Whyte22:39

       Huh?

   27. LFLex Fridman22:39

       We're, uh, actually when we're talking about cheap, we're thinking, like, asymptotically, like-

   28. DWDennis Whyte22:43

       Oh.

   29. LFLex Fridman22:43

       ... if you take it forward-

   30. DWDennis Whyte22:45

       Yeah.
4. 32:58 – 38:10

   Fission vs fusion

   1. DWDennis Whyte32:58

   2. LFLex Fridman32:58

      So, we'll return to MIT's Plasma Science and Fusion Center-

   3. DWDennis Whyte33:01

      Sure.

   4. LFLex Fridman33:01

      ... but let us linger on the, uh, destruction of human civilization, uh, which brings us to the topic of nuclear fission. What is that? Wh- uh, so the, the process that is inside, uh, nuclear weapons and current nuclear power plants.

   5. DWDennis Whyte33:16

      So, it relies on the same underlying physical principle, but it's exactly the opposite-

   6. LFLex Fridman33:22

      Mm-hmm.

   7. DWDennis Whyte33:22

      ... of fu- which actually the names imply. Fusion means bringing things together. Fission means splitting things apart.

   8. LFLex Fridman33:28

      Mm-hmm.

   9. DWDennis Whyte33:28

      So, fission, uh, requires the heaviest instead of the lightest and the most unstable versus the most stable, uh, uh, elements. So, this tends to be uranium, uh, or plutonium, p- primarily uranium. So, take uranium. So, uranium-235 is one of the he- uh, that, this is one of the heaviest unstable elements. And what happens is that this is, uh, and f- uh, fission is triggered by the fact that one of these subatomic particles, the neutron, which has no electric charge, basically gets i- in proximity enough to this, uh, and, and triggers an instability, uh, effectively inside of this uns- what is teetering on the border of instability and basically splits it apart. And that's the fission, right? The fis- fissioning. Um, and so when that happens because the products that are in, in kind of, it roughly splits in two, but it's not even that. It's actually more complicated. It splits into this whole array of lighter elements and nuclei. A- and when that happens, there's less rest mass, uh, uh, l- left than the, than the original one. A- so it's actually the same. So, it's again, it's rearrangement of the strong nuclear force that, that's happening. Um, but that's the source of the energy. And so in the end, it's like, so this is a famous graph that we show everybody is, is basically it turns out every element that exists in the periodic table, all the things that make up everything-

   10. LFLex Fridman34:55

       Mm-hmm.

   11. DWDennis Whyte34:56

       ... have, uh, have a, remember y- you asked a good question. It was like, "So, should we think of mass as being the same as stored energy?" Yes. So, you can make a plot that basically shows the relative amount of stored energy in all of the elements that are stable and make up basically the world, okay, and the universe. And it turns out that this one has a maximum amount of, of stability or storage, uh, at iron.

   12. LFLex Fridman35:23

       Okay.

   13. DWDennis Whyte35:24

       So, it's kind of in the middle of the periodic table because this goes from, you know, it's r- it's roughly that. And so this, what that means is that if, um, if you take something heavier than iron, like uranium, which is, which is more than twice as heavy th- that, and you split apart, if somehow just magically you can just split apart its constituents, and you get something that's lighter, that will, because it moves to a more stable energy state, it releases kinetic energy. That's the energy that we use. Kinetic energy meaning the movement of things. So, it's actually an energy you can do something with. And fusion sits on the other side of that because it's also moving towards iron, but it's do, it has to do it through fu- fusion together. So, this leads to some pretty profound differences. As I said, they have some underlying physics or science, um, uh, proximity to each other, but they're literally the opposite. So, fusion, uh, why is this... It actually goes into practical implications of it, which is that fission can happen at room temperature. It's because there's, this neutron has no...... electric charge, and therefore roo- it's literally room temperature neutrons that actually trigger the reaction. So this means, um, a-in order to establish, uh, what's going on with it, and it works by chain reaction, is that you can do this at room temperature. So Enrico Fermi did this, like, on a, on a university campus, University of Chicago campus. The first sustained, you know, chain reaction was done underneath a squash court with big blocks of graphite, you know? It was still an, I mean, don't get me wrong, an incredible human achievement, right? But that's, you know... And then you think about fusion. I have to build a contraption of some kind that's going to get to 100 million degrees. Okay, wow, that's a big difference. The other one is about the chain reaction, that namely fission works by the fact that when that fission occurs, it actually produces free neutrons. Free neutrons, particularly if they get slowed down to room temperature, trigger, can trigger other fission reactions if there's other uranium nearby or fissile materials. So this means that the way that it releases energy is that you set this up in a very careful way such that every, on average, every reaction that happens exactly releases enough neutrons and slows down that they actually make another reaction, one, exactly one. And th- what this means is that because each reaction releases a fixed amount of energy, blah, blah, blah, you do this, and then in time, this looks like just a constant power output. So that's how our fission power plant works.

   14. LFLex Fridman37:52

       And so there control the fi- the chain reactions-

   15. DWDennis Whyte37:54

       Yes.

   16. LFLex Fridman37:54

       ... is extremely difficult and extremely important for-

   17. DWDennis Whyte37:56

       It's very important.

   18. LFLex Fridman37:58

       ... fission.

   19. DWDennis Whyte37:58

       And when you intentionally design it that it, it creates more than one-

   20. LFLex Fridman38:01

       Mm-hmm.

   21. DWDennis Whyte38:02

       ... fission reaction per, per starting reaction, then it exponentiates away.

   22. LFLex Fridman38:07

       Mm-hmm.

   23. DWDennis Whyte38:08

       But which is, which is what a nuclear weapon

5. 38:10 – 41:56

   Nuclear weapons

   1. DWDennis Whyte38:10

      is.

   2. LFLex Fridman38:10

      Yeah, so h- how does an atomic weapon work? How does a hydrogen bomb work? Asking for a friend.

   3. DWDennis Whyte38:15

      Yeah. (laughs) Yeah, so, um, a- at its heart, what it ha- what you do is you very quickly put together enough of these materials that can undergo fission with room temperature neutrons.

   4. LFLex Fridman38:28

      Mm-hmm.

   5. DWDennis Whyte38:28

      And you put them together fast enough that what happens is that the, this process can essentially grow mathematically, like very fast.

   6. LFLex Fridman38:36

      Hm.

   7. DWDennis Whyte38:36

      And so this releases large amounts of energy. So that's the underlying reason that it works. So you've heard of a fusion weapon. So this is interesting is that it is, it, but it's dislike fusion energy in the sense that what happens is that you're using fusion reactions to, but it's simply, it increases the gain actually of the weapon rather than, um, it- it- it's not a pure... At- at its heart, it's still a fission w- weapon. You're just using fusion reactions as a sort of intermediate catalyst basically to ma- to get even more energy out of it. But it's not directly applicable to, to be used in, in energy source.

   8. LFLex Fridman39:14

      Does it terrify you, just, again, to step back at the philosophical, that humans have been able to use physics and, uh, engineering to create such powerful weapons?

   9. DWDennis Whyte39:28

      I wouldn't say terrify. I mean, we should be... (laughs) This is the, this is the progress of, of human- every time that we've gotten access, you talk, you know, the day the universe changed, things really changed when we got access to new kinds of energy sources. But every time you get ac- and typically what this meant was you get access to more intense energy, right? That's, and that's what that was. And so the ability to move from burning wood to using coal to using gasoline and petroleum and then finally to use this is that, is that both the potency and the consequences a- are elevated a- around those things.

   10. LFLex Fridman40:08

       It's just like you said, the, the way that fusion, nuclear fusion would change the world, I don't think, u- unless we think really deeply, we'll be able to anticipate some of the things we can create. There's go- going to be a lot of amazing stuff.

   11. DWDennis Whyte40:22

       Yeah.

   12. LFLex Fridman40:22

       But then that amazing stuff is gonna enable more amazing stuff and more, unfortunately, or, uh, depending how you see it, m- more powerful weapons.

   13. DWDennis Whyte40:31

       Well, yeah, but see, that's the thing. Fusion breaks that trend-

   14. LFLex Fridman40:36

       Mm-hmm.

   15. DWDennis Whyte40:36

       ... in the following way. So one of the... So fusion doesn't work on a chain reaction. There's no chain reaction. Zero. So this means it cannot physically exponentiate away on you 'cause it works... And actually this is why star... By the way, we know this already. It's why stars are so stable, why most stars and suns are so stable. It's because they are regulated through their own temperature and their heating. Because what's happening is not that there's some probability of this exponentiating away, it's that the energy that's being released by fusion basically is keeping the fire hot.

   16. LFLex Fridman41:11

       (laughs)

   17. DWDennis Whyte41:11

       Um, and these tend to be, you know, and when it comes down to thermodynamics and things like this, there's a reason, for example, it's pretty easy to keep a constant temperature like in an oven and things like this. It's the same thing in fusion. So this is actually one of the features that I would argue fusion breaks the, breaks the trend of this is that it's, it has more energy intensity than, than, than fission on, on paper, but it actually does not have the consequences of control and sort of rapid release of the energy because it's actually... It, it, the physical system just doesn't want to do that. Yeah.

   18. LFLex Fridman41:48

       We're gonna have to look elsewhere for the weapons with which we fight World War III. Fair enough. Uh, so

6. 41:56 – 49:07

   Plasma

   1. LFLex Fridman41:56

      what is plasma-

   2. DWDennis Whyte41:58

      Hm.

   3. LFLex Fridman41:58

      ... that you may or may have not mentioned? You mentioned ions and electrons and so on.

   4. DWDennis Whyte42:01

      I did not mention plasma.

   5. LFLex Fridman42:02

      So what is plasma? What is the role of plasma in nuclear fusion?

   6. DWDennis Whyte42:06

      So plasma is a phase of matter or a state of matter, so-Unfortunately, our schools don't... (laughs) It's like, I'm not sure why this is the case, but, eh, all, all children l-learn the three phases of matter, right? So, and what does this mean? So, we'll take, like, water as an example. So if you c- if it's cold, it's ice. It's in a solid phase, right? And then if you heat it up, the temp- it's the temperature that typically depends, uh, uh, sets the phase, although it's not, it's, it's not only temperature. So, you heat it up, and you go to a liquid, and obviously it changes its physical properties 'cause it can, you can pour it and so forth, right? And then if you heat this up enough, it turns into a gas, and a gas behaves differently because there's a very sudden change in the density. Actually, that's what's, what's happening. So, it, it changes by about a factor of 10,000 in density from the, from the liquid phase into when you make it into steam at atmospheric pressure. All very good, eh, except the problem is they forgot, like, what happens if you just keep elevating the temperature?

   7. LFLex Fridman43:03

      You don't wanna give kids ideas.

   8. DWDennis Whyte43:04

      (laughs)

   9. LFLex Fridman43:05

      They're gonna start experimenting. They're gonna start heating up the gas.

   10. DWDennis Whyte43:08

       Well, they're like, "It's good to, it's good to start to..." Anyway, so you, um, yeah, it turns out that once you get above, it's approximately 5,000 or 10,000 degrees Celsius, then you hit a new phase of matter. And actually, that's the phase of matter that is for all, uh, pretty much all the temperatures that are above that, uh, as well too. Um, and so what does that m-mean? So, it actually changes phase, so it's a different state of matter. And the reason that it becomes a different state of matter is that it's hot enough, that what happens is that the atoms that make up, remember, go back to Feynman, right? Everything's made up of these individual things, these atoms, but atoms can actually themselves be, um, w- which are c- which are made of nuclei, which contain the positive, uh, particles and the neutrons and then the electrons, which are very, very light, very much less mass than, than the nucleus, and that surround this. This is what makes up an atom. So, a plasma is what happens when you start pulling away enough of those electrons that, that they're free from the ion. So almo- all the atoms that make up, uh, uh, us, up and this water and all that, the electrons are in tightly bound states, and basically they're extremely stable. Once you're at about 5,000 or 10,000 degrees, you start pulling off the electrons. And what this means is that now the medium that is there, its constituent particles have mostly have net charge on them. So, why does that matter? It's because n- now this means that the particles can interact b- through their electric charge. In some sense, they were when it was in the atom as well too, but now that they're free particles, this means that they start, it fundamentally changes the behavior. It doesn't behave like a gas. It doesn't behave like a solid or a liquid. It behaves like a plasma, right? And so wh- why is this, (laughs) why is it disappointing that we don't speak about this? It's because 99% of the universe is in the plasma state. It's called stars. And in fact, our own sun, at the center of the sun is, well, clearly a plasma, but actually the surface of the sun, which is around 5,500 Celsius, is also a plasma 'cause it's hot enough, that is, uh... In fact, the things that you see... Sometimes you see these pictures from the surface of the sun, amazing f- (laughs) like, satellite photographs of, like, those big arms of things and of light coming off of the surface of the sun and solar flares, those are plasmas.

   11. LFLex Fridman45:27

       What are some interesting ways that this fourth state of matter is different than gas?

   12. DWDennis Whyte45:32

       Let's go to how a gas works, right? So, the reason a ga- and it goes back to Feynman's brilliance in saying that this is the most important concept. The reason g- actually solid, f- (laughs) liquid, and gas phases work is because the w- the nature of the interaction between the atoms changes. And so in a gas, you can think of this as being this room and the things, uh, although you can't see them, is that the molecules are flying around, but then with some frequency they basically bounce into each other.

   13. LFLex Fridman46:00

       Mm-hmm.

   14. DWDennis Whyte46:00

       And when they bounce into each other, they exchange momentum and energy around on this. And so it turns out that the probability and the distances and the scattering of those, of what they do, it, it's, it's those interactions that set the, uh, about how a gas behaves.

   15. LFLex Fridman46:19

       Mm-hmm.

   16. DWDennis Whyte46:19

       So, what does he mean by this? Well, so for example, if I take a t- a, a, an i- a, an imaginary test particle of some kind, like I spray something into the air that's got a particular color, or in fact you can do it in liquids as well too, like, how it, uh, gradually will s- disperse away from you. This is s- this is fundamentally set because of the way that those particles are bouncing into each other.

   17. LFLex Fridman46:40

       The, the probabilities of those, uh, particle bouncing.

   18. DWDennis Whyte46:43

       Yeah, the rate that they go at and the distance that they go at and so forth. So, this was figured out by Einstein and others at the beginning of the, b- Brownian motion, all these kinds of things. These were, these were set, um, up at the beginning of the last century, and it was really, like, this great revelation. "Wow, this is why matter behaves the way that it does, like, wow." Um, um, so but it's really like... And, and also in liquids and in solids, like, what really matters is, is, is, is how you're interacting with your nearest neighbor.

   19. LFLex Fridman47:12

       Mm-hmm.

   20. DWDennis Whyte47:13

       So, you think about that one. The gas particles are basically going around. Until they, until they actually hit into each other though they don't really exchange information And it's the same in a liquid. You're kind of beside each other, but you can kinda move around. And in a solid, you're literally, like, stuck beside your neighbor. You can't move, like Yeah. 　 Plasmas are, uh, are weird in the sense is that they're, it's not like that. So, and it's because the particles have electric charge, this means that they can push against each other without actually being in c- close proximity to each other. It's, it's not, that's not an infinitely true statement, which if we go together, it's a little bit more technical. But basically, this means that you can start having action or exchange of information at a distance. And that's, in fact, the definition of a plasma is that it says the, these have a technical name, it's called a Coulomb collision, it just means that it's dictated by this force which is being pushed between the charged particles, is that, uh, the definition of a plasma is a, is a medium in which the collective behavior is dominated by these collisions at a distance. So, you can imagine, then, this starts te- to, to give you some strange...... behaviors, um, uh, which I could, I could quickly talk about, like, for exa- one of the most (laughs) counterintuitive ones is as plasmas get more hot, as they get h-h-high in temperature, then the collisions happen less frequently. It's, like, like, "What? That doesn't make any sense." When particles go faster, you think they would collide more often. But because the particles are interacting through, interacting through their electric field when they're going faster, they actually spend less time-

   21. LFLex Fridman48:51

       Mm-hmm.

   22. DWDennis Whyte48:51

       ... in the influential field of each other, and so they talk to each other less in an energy and momentum exchange point of view.

   23. LFLex Fridman48:58

       Interesting.

   24. DWDennis Whyte48:58

       It's just, well, just one of the count- one of the counterintuitive aspects of plasmas. (laughs)

   25. LFLex Fridman49:02

       Which is probably very, uh, relevant for nuclear fusion.

   26. DWDennis Whyte49:06

       Yes, exactly.

7. 49:07 – 1:04:27

   Nuclear fusion reactor

   1. DWDennis Whyte49:07

   2. LFLex Fridman49:07

      So if I can try to summarize what a nuclear fusion reactor is supposed to do, so you have, what, a couple of elements? What are usually the elements?

   3. DWDennis Whyte49:19

      Usually deuterium and tritium, which are the heavy forms of hydrogen.

   4. LFLex Fridman49:22

      Hydrogen. You have those, and you start heating it. And then as you start heating it, I forgot the temperature you said, but it becomes plasma.

   5. DWDennis Whyte49:29

      About 100 million, yeah.

   6. LFLex Fridman49:29

      No, first. First, it becomes-

   7. DWDennis Whyte49:31

      Oh, first, it becomes plasma.

   8. LFLex Fridman49:32

      ... plasma.

   9. DWDennis Whyte49:32

      So it's, it's a gas-

   10. LFLex Fridman49:33

       Yeah.

   11. DWDennis Whyte49:33

       ... and then it turns into a plasma-

   12. LFLex Fridman49:35

       Right.

   13. DWDennis Whyte49:35

       ... at about 10,000 degrees.

   14. LFLex Fridman49:36

       And then so you have a bunch of electrons and ions flying around, and then you keep heating the thing.

   15. DWDennis Whyte49:41

       Yep.

   16. LFLex Fridman49:42

       And, uh, I guess as you heat the thing, the ions hit each other rarer and rarer?

   17. DWDennis Whyte49:47

       Yes.

   18. LFLex Fridman49:47

       So, oh man, that's not fun.

   19. DWDennis Whyte49:48

       (laughs)

   20. LFLex Fridman49:49

       So you have to keep hea-

   21. DWDennis Whyte49:50

       Yes.

   22. LFLex Fridman49:50

       ... heating it, um, such that, uh, you, you have to keep hitting it until the probability of them colliding becomes reasonably high.

   23. DWDennis Whyte50:00

       And so it turns-

   24. LFLex Fridman50:01

       And also on top of that, and sorry to interrupt, you have to prevent them from hitting the walls-

   25. DWDennis Whyte50:07

       Exactly.

   26. LFLex Fridman50:07

       ... of the reactor-

   27. DWDennis Whyte50:08

       Yes, exactly.

   28. LFLex Fridman50:09

       ... somehow.

   29. DWDennis Whyte50:09

       So you asked about the r- the, the definitions of the requirements for fusion, so the most famous one or in some sense the most intuitive one is the temperature. And the reason for that is that you, you can make many, many kinds of plasmas that have zero fusion going on in them. And the reason for this is that the average, so , you can make a plasma at around 10,000. In fact, if you come ... By the way, you're welcome to come to our laboratory at the PSFC. I can show you a demonstration of a plasma-

   30. LFLex Fridman50:37

       Mm-hmm.
8. 1:04:27 – 1:25:04

   2022 nuclear fusion breakthrough explained

   1. LFLex Fridman1:04:27

      Let's, so you have experience with, uh, magnetic confinement. You have experience with inertial confinement. Most of your work has been in magnetic confinement.

   2. DWDennis Whyte1:04:33

      Yes, yeah.

   3. LFLex Fridman1:04:34

      But let's sort of, um, talk about the, the, the, the sexy recent thing for, for a bit of a time. There's been a breakthrough in the news, uh, that, uh, laser-based inertial confinement was used by DoE's National Ignition Facility at the Lawrence Livermore National Laboratory. Can you explain this breakthrough that happened in December?

   4. DWDennis Whyte1:04:56

      Yeah. So, it goes to the set of criteria that I talked about before about getting high energy gain. So, in the end, what, what are we after in fusion is that we, we basically assemble this plasma fuel in some way, and we provide it a starting amount of energy. Think of lighting the fire. And what you want to do is get back, like, m- significant excess gain-

   5. LFLex Fridman1:05:23

      Mm-hmm.

   6. DWDennis Whyte1:05:23

      ... from the fact that the fusion is, is making more, uh, is releasing the energy. So, it's, it's like the equivalent of, like, we wanna have a match, a small match light a fire, and then the fire keeps us hot.

   7. LFLex Fridman1:05:34

      Mm-hmm.

   8. DWDennis Whyte1:05:34

      It's like, it's, it's very much like that. So, as I said, we've, we've made many of the, and what do we mean by we? It's like the fusion community has pursued aspects of this through a variety of different confinement, uh, methodologies. Um, is that the, um, the key part about what happens... So, what was a threshold we had never gotten over before was that if you only consider the plasma fuel, not the, not the total engineering system but just the plasma fuel itself, we had not gotten to the point yet where basically the size of the match was, was smaller than the amount of energy that we got from the fusion.

   9. LFLex Fridman1:06:11

      Mm-hmm. Is there a good term for when the output is greater than the input?

   10. DWDennis Whyte1:06:17

       Yes, yes. It, it, there is. Well, there's several special definitions of this. So, one of them is that if you l- if you, like in a fire, if you light a match-... and you have it there, and it's an infinitesimal amount of energy compared to what you're getting out of the fire. We call this ignition.

   11. LFLex Fridman1:06:32

       Mm-hmm.

   12. DWDennis Whyte1:06:33

       Which makes sense, right? This is like what the s- the, the what our own sun is as well too. So, that, that was not ignition in that sense, uh, as well too. So, what we call this is scientific, what the one that we, I just talked about, which is for, for some instance, when I get enough fusion energy released compared to the size of the match, we call this scientific breakeven.

   13. LFLex Fridman1:06:54

       Breakeven.

   14. DWDennis Whyte1:06:55

       Breakeven. And it's because you've gotten past the fact that this is unity now at this point.

   15. LFLex Fridman1:07:00

       What is a fusion gain or as, uh, using the notation Q from the paper overview of the-

   16. DWDennis Whyte1:07:05

       Yeah.

   17. LFLex Fridman1:07:05

       ... SPARC tokamak before to-

   18. DWDennis Whyte1:07:07

       Yeah.

   19. LFLex Fridman1:07:07

       ... using just the same kind of terminology-

   20. DWDennis Whyte1:07:08

       Yeah, actually, so there's, uh, sorry, the technical term is Q, uh, capital Q.

   21. LFLex Fridman1:07:13

       Oh, so it's good. People actually use Q for this purpose.

   22. DWDennis Whyte1:07:15

       We actually use capital Q, yeah. Or sometimes it's called Q-

   23. LFLex Fridman1:07:18

       So, Q's taken?

   24. DWDennis Whyte1:07:18

       Q sub p or something like this.

   25. LFLex Fridman1:07:20

       Okay.

   26. DWDennis Whyte1:07:20

       Okay, so this is, which, which means the, which wha- what it means is that it's in the plasma. So, all we're considering is, is the energy balance or gain that comes from the plasma itself.

   27. LFLex Fridman1:07:30

       Mm-hmm.

   28. DWDennis Whyte1:07:30

       We're not considering the technologies which are around it which are providing the containment and so forth. So, wh- why, why the excitement and so f- well, because f- for one reason, it's a rather sim- it's a rather simple threshold to get over, to understand that you're getting more energy out from the fusion, even in a theoretical sense than you were from the, you know, from the ini- uh, starting match.

   29. LFLex Fridman1:07:52

       Do you mean conceptually simple?

   30. DWDennis Whyte1:07:53

       It's conceptually simple that you get past one that everyone under- like, when you're less than one, that's much less-

Episode duration: 3:08:06