Audio · 2025-11-17 · 6 moments

#485 – David Kirtley: Nuclear Fusion, Plasma Physics, and the Future of Energy

David Kirtley is a nuclear fusion engineer and CEO of Helion Energy, a company working on building the world’s first commercial fusion power plant by 2028. Thank you for listening ❤ Check out our sponsors: https://lexfridman.com/sponsors/ep485-sc See below for timestamps, transcript, and to give feedback, submit questions, contact Lex, etc. Transcript: https://lexfridman.com/david-kirtley-transcript CONTACT LEX: Feedback – give feedback to Lex: https://lexfridman.com/survey AMA – submit q ✦ AI generated

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Context◆

Fusion is the process that powers the universe—stars, plants, fossil fuels—and yet we have not actively used it to generate electricity on Earth.

David Kirtley introduces fusion as the fundamental energy source of the cosmos, which has enabled life on Earth indirectly, but notes the irony that humanity has not yet built a fusion power plant for direct electricity generation.

transcript

David Kirtley: 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.

Data

The fuel for fusion—deuterium found in seawater—is so abundant that it could power humanity at current consumption levels for 100 million to a billion years, and it cannot be monopolized by any country.

Kirtley explains that deuterium, a heavier isotope of hydrogen found in all water on Earth, provides an essentially limitless fuel supply for fusion. He notes that because every country has access to seawater, no nation can control the fuel supply or cut pipelines.

transcript

David Kirtley: 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. ... The fuel is in seawater all over Earth. Everybody has deuterium. And everybody has it. And so you can't have a monopoly on the fuel. And no one can control the fuel and no one can turn off the fuel. No one can cut a pipeline. That just cannot happen with fusion.

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Mechanism

Fusion is hard and fission is easy—fission happens at room temperature as a self-sustaining chain reaction, while fusion requires overcoming powerful electromagnetic repulsion at 100 million degrees.

Kirtley contrasts the ease of fission—where uranium and plutonium are so unstable that simply adding a neutron triggers a chain reaction at room temperature—with the difficulty of fusion, which requires heating fuel to 100 million degrees to overcome electromagnetic repulsion before the strong nuclear force can take effect.

transcript

David Kirtley: I think fundamentally it's that in a lot of ways, fusion is hard and fission is easy. 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. 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. ... you take these lightweight isotopes like hydrogen and deuterium. And as you combine them and take these molecules and get them closer and closer together, some really interesting fundamental physics happens. So first, these atomic nuclei are charged. They have an electric charge. And they, like charges, repel. ... 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.

Claim

Fusion power plants cannot be used to make nuclear weapons, which is a critical distinction from fission reactors whose fuel can be diverted for weapons purposes.

Kirtley explains that fusion processes are fundamentally different from the fission processes used in nuclear weapons, and that proliferation experts are urging rapid development of fusion to prevent the global spread of enriched uranium.

transcript

David Kirtley: Fusion power plants can't be used to make nuclear weapons. Fundamentally, that 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 started in fusion, and most of our team thinks about the mission of fusion of delivering clean, safe electricity, is that it also can't be used to make weapons. ... 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 so they are pushing us as fast as possible. Go build fusion generators and get them deployed everywhere.

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Claim◆

Fusion is fundamentally safe because the reaction is not self-sustaining—you have only one second of fuel in the system at any time, so if anything goes wrong, the reaction stops immediately.

Kirtley explains that fusion generators automatically shut off when fuel input stops, and at any moment contain only a second's worth of fuel, unlike fission reactors which hold years of fuel in the core.

transcript

David Kirtley: Yes, fusion power is fundamentally safe. The physics and the reactions of the fusion system itself means you don't have runaways. ... In a fusion generator, you are continuously 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 for whatever reason, 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 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 issue.

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Mechanism

Helion's approach uses a field-reversed configuration (FRC), where the plasma generates its own magnetic field and traps itself, rather than being trapped by external magnets like in a tokamak or stellarator.

Kirtley describes the key physics insight behind Helion's approach: by rapidly reversing the magnetic field in a millionth of a second, the plasma self-organizes into a closed field where it generates its own magnetic field and traps itself, analogous to the plasmoids seen in solar flares.

transcript

David Kirtley: In a magnetic coil, when you have a round electrical coil, you have electrical current flowing in that coil. ... In a theta pinch, and for a mirror, and for a tokamak, in that magnetic field, the plasma gets trapped. But in an FRC, this electrical current is the plasma. And that plasma then generates its own magnetic field. And it's then trapped on its own magnetic field. That's fascinating. And that's the key. And so in your tokamak, in your donut, and in your funky donut, your stellarator, you make the magnets and you trap your plasma in it. In an FRC, you make the plasma, which makes the magnets, and it traps itself. ... You have to reverse the electrical current faster than a million degree, which is a very hot gas particle can move. And so that means we have to do it on the order of a millionth of a second.

Highlight slides

Fusion Powers the Universe✦ from: Fusion is the process that powers the universe—stars, plants, fossil fuels—and yet we have not actively used it to generate electricity on Earth.The Irony of Fusion Energy✦ from: Fusion is the process that powers the universe—stars, plants, fossil fuels—and yet we have not actively used it to generate electricity on Earth.Fusion Is Fundamentally Safe by Design✦ from: Fusion is fundamentally safe because the reaction is not self-sustaining—you have only one second of fuel in the system at any time, so if anything goes wrong, the reaction stops immediately.Catastrophic Events Also Cannot Trigger Fusion✦ from: Fusion is fundamentally safe because the reaction is not self-sustaining—you have only one second of fuel in the system at any time, so if anything goes wrong, the reaction stops immediately.

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Fusion is the process that powers the universe—stars, plants, fossil fuels—and yet we have not actively used it to generate electricity on Earth.

The fuel for fusion—deuterium found in seawater—is so abundant that it could power humanity at current consumption levels for 100 million to a billion years, and it cannot be monopolized by any country.

Fusion is hard and fission is easy—fission happens at room temperature as a self-sustaining chain reaction, while fusion requires overcoming powerful electromagnetic repulsion at 100 million degrees.

Fusion power plants cannot be used to make nuclear weapons, which is a critical distinction from fission reactors whose fuel can be diverted for weapons purposes.

Fusion is fundamentally safe because the reaction is not self-sustaining—you have only one second of fuel in the system at any time, so if anything goes wrong, the reaction stops immediately.

Helion's approach uses a field-reversed configuration (FRC), where the plasma generates its own magnetic field and traps itself, rather than being trapped by external magnets like in a tokamak or stellarator.

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