David Kirtley — Nuclear engineer and CEO of Helion Energy, a fusion company building pulsed magneto-inertial fusion generators. His team has built seven prototype systems and signed a deal to deliver fusion power to Microsoft.
The gist
David Kirtley walks Lex Fridman through the fundamentals of nuclear fusion versus fission, why fusion is inherently safe, can't be used for weapons, and draws fuel (deuterium) from seawater. He explains Helion's distinctive approach: a linear, pulsed magneto-inertial system using a field-reversed configuration that self-organizes a closed-field plasma and lets electricity be recovered directly rather than through a steam turbine. Much of the conversation centers on the engineering and manufacturing philosophy that lets Helion iterate fast, build small and mass-producible systems, and even buy parts off eBay. Kirtley discusses the 2023 Microsoft deal targeting first fusion electricity to the grid by 2028, the coupling of fusion with AI data centers, and a long-term vision of energy abundance. The episode closes with reflections on the Kardashev scale, the Fermi paradox, and the beauty of physics.
Big reveals
- Fusion combines light hydrogen atoms (like the Sun), yielding clean fuel from water, no long-lived radioactive waste, no meltdown risk, and no carbon emissions.
- Fusion power plants cannot be used to make nuclear weapons; even the hydrogen bomb is fundamentally a fission bomb, with ~90% of an H-bomb's energy coming from uranium reactions.
- A Helion fusion system holds only about one second of fuel at any time, so if fuel input stops, fusion simply stops, making it fundamentally safe.
- Rapidly reversing the magnetic field (in about a millionth of a second) causes the plasma to self-organize internally into a closed-field configuration that traps itself on its own magnetic field.
- Helion's high-beta pulsed system recovers electricity directly via the expanding magnetic field (like a piston engine), targeting ~80% efficiency versus ~30-35% for steam turbines.
- In 2023 Helion signed a deal with Microsoft to build a grid-connected fusion power plant, with an ambitious target of first electrons by 2028.
- Helion's design philosophy is to mass-produce small components (e.g., 100 small magnets instead of one giant one) and even source parts like vacuum pumps from eBay to move fast.
- A 50-megawatt Helion facility is believed to fit in a 27,000 square foot building (about an acre), versus roughly 2,000 acres of solar in Seattle for the same output.
Things worth remembering
- Seawater holds enough deuterium fuel to power all of humanity's current electricity use via fusion for an estimated 100 million to a billion years.
- The ADVANCE Act, codified into law last year, established for the first time how the U.S. will regulate fusion, treating it like a particle accelerator under Part 30 (the same statutes as hospitals).
- When Helion applied for its first fusion shielding permit as a particle accelerator, the first question regulators asked was 'where do the patients go?' because the form assumed a hospital; Helion's first license came in 2020.
- Helion's systems run on the order of 100 million amps of electrical current, compared to a typical home's 200-amp breaker box.
- Pioneering theta-pinch fusion work in 1958 reached 50 million degrees by switching millions of amps in microseconds, all before transistors and CPUs existed.
- Helion uses deuterium and helium-3 fuel; the helium-3 nucleus is called a 'helion,' which is the origin of the company's name.
- Helium-3 is rare on Earth because it's lightweight and escapes into space, but Jupiter holds massive amounts of it.
- Helion's prototypes were named after beer and then Starbucks cup sizes (Tall, Grande, Venti, Trenta); Trenta came online in 2020 as the first to achieve 100 million degrees and bulk deuterium-helium-3 fusion.
- Helion's fusion control code includes Fortran, Python, Java, and assembly-language programming on FPGAs, with electrical switches triggered via fiber optics at nanosecond speeds.
- Helion has run a small fusion system at 100 pulses per second for over a billion operations, demonstrating they can dial power output up and down to match grid demand.