David Kirtley: Nuclear Fusion, Plasma Physics, and the Future of Energy | Lex Fridman Podcast #485

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

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.