Lex Fridman Podcast #485 – David Kirtley: Nuclear Fusion, Plasma Physics, and the Future of Energy
November 17, 2025

Episode Overview

Lex Fridman sits down with David Kirtley, CEO of Helion Energy and a leading expert in nuclear fusion, for a deep technical and philosophical conversation about fusion energy, plasma physics, and what it would mean for the future of civilization. The discussion traverses the fundamental physics of fusion and fission, granular details of Helion’s pulsed magneto-inertial approach, the safety, waste, and geopolitical implications of fusion, and the cultural and practical realities of rapidly iterating in cutting-edge energy technology. This episode is a must for anyone interested in the potential of limitless clean energy and the mechanics and mindsets pushing technology forward.

Key Discussion Points & Insights

1. What is Nuclear Fusion? (Starts ~[11:43])

• Fusion vs. Fission:
  • Fusion is the reaction that powers the stars, combining light elements (hydrogen isotopes) into heavier elements, releasing vast amounts of energy.
  • Fission splits heavy elements (like uranium), creating energy but also long-lived radioactive wastes.
  • “Fusion is what powers the universe... but ironically, we don't do it actively here on Earth to make electricity yet.” (Kirtley, [11:43])
• Fuel Abundance:
  • Fusion fuel (like deuterium) is extracted from ordinary water on Earth, making it effectively limitless for human purposes.
  • “We estimate that in seawater here on Earth we have... between 100 million years and a billion years of fuel.” (Kirtley, [18:23])
• Fundamental Physics:
  • E=mc² governs energy release for both reactions; the “mass defect” as two nuclei fuse translates into explosive amounts of energy.
• Types of Fusion Fuels:
  • Deuterium and tritium are standard, but Helion is focused on deuterium and helium-3 for higher efficiency and direct electricity extraction.

2. Safety & Waste of Fusion vs. Fission ([26:59], [30:43], [40:47])

• Inherent Safety:
  • Fusion can’t sustain runaway reactions; “...if you stop putting fuel into that system, fusion just stops.” (Kirtley, [40:47])
  • Unlike fission, a fusion generator can’t melt down or cause major catastrophe—at worst, only seconds of fuel are lost.
• Waste Profile:
  • Fusion creates some radiation (x-rays, neutrons), but no long-lived radioactive waste or proliferation risk.
  • Shielding is essential, but waste concerns are minimal compared to fission: “The answer is, you don’t need to evacuate the populace nearby the fusion power plant.” (Kirtley, [40:47])
• Fission Plant Safety:
  • Kirtley emphasizes that modern fission reactors are also engineered to be safe, and most historical disasters were “fundamentally human failures rather than engineering failures.” (Kirtley, [32:23])

3. Nuclear Weapons & Proliferation ([34:14], [36:14])

• Fusion and Weapons:
  • Power-plant fusion cannot be harnessed for weapons; fusion bombs still require a fission-based primary reaction.
  • Proliferation risks come from fission fuels (uranium, plutonium), not fusion.
  • Proliferation experts worldwide encourage fusion deployment to reduce temptation of uranium enrichment globally.
• Geopolitical Impacts:
  • Fusion erases the monopolies on energy: “Everyone has deuterium... no one can control the fuel.” (Kirtley, [40:03])

4. The Physics & Engineering of Fusion ([47:28] onward)

• Major Fusion Approaches:
  • Inertial fusion (lasers rapidly squeezing fuel—e.g., NIF)
  • Magnetic confinement (tokamaks, stellarators) trapping plasma in magnetic fields
  • Helion’s approach: Pulsed Magneto-Inertial Fusion, specifically using Field Reversed Configurations (FRC)
• Tokamak vs. Stellarator vs. FRC:
  • Tokamaks and stellarators use continuous magnetic fields to “trap” hot plasma.
  • FRCs use self-organizing plasmas formed by ultra-fast magnetic field reversals—enabled only recently by advances in semiconductor switching.
• Technical Challenges:
  • High “beta” (ratio of plasma pressure to confining magnetic field energy) gives FRCs their efficiency, but also makes stability tricky.
  • Stability is managed by tailoring the system’s inertia, geometry, and speed (the “S*/E” parameter): “If you spin it fast enough, it will stay upright, even though it wants to just fall over...” (Kirtley, [76:26])

5. The Quest for High Temperatures:

• Why 100 Million Degrees?
  • Collisions for fusion require particles to move at ~1 million miles per hour ([83:41]).
  • Achieved using extreme electrical pulses and magnetic compression with shot-to-shot operation happening faster than a human can blink.
• Controlling the System:
  • Fusion pulses are pre-programmed and executed via assembly-level commands and FPGAs, using Python, Java, and Fortran for simulation, with diagnostics relayed over fiber optics for massive parallel switching ([85:29]).
  • High-speed cameras and spectroscopic diagnostics capture fleeting moments of plasma and fusion events ([137:12]).

6. Numerical Simulation and Artificial Intelligence ([91:09], [95:08])

• Simulation's Central Role:
  • Designs use MHD (magneto-hydrodynamics), circuit models, and, increasingly, GPU-accelerated particle-in-cell codes.
  • AI and reinforcement learning are beginning to shorten the iterative cycle between experiments and models.
• Fusion Scaling Law:
  • Fusion output scales as the magnetic field raised to ~3.8 power ([99:10]). Thus, pulsed systems, capable of very high field strengths, offer big advantages.

7. Direct Electricity Extraction vs. Steam ([103:41], [104:05])

• Traditional Fusion/Tokamak:
  • Most fusion machines generate heat, which boils water to spin turbines—maxing out at ~30% efficiency due to thermodynamic limits.
• Helion's Pulsed High-Beta System:
  • Allows much of the fusion energy (from charged particles) to be directly captured as electricity, possibly at 80–85% efficiency.
  • Enables higher net output, faster operations, and modularity.

8. Advanced Fuels: Deuterium–Helium-3 Path ([111:34])

• Advantages & Costs:
  • D–He3 fusion produces all-charged-particle output (no neutrons), perfect for direct energy recovery, but requires higher temperatures (200–300 million °C) and larger machines.
  • Helium-3 is rare on Earth but abundant on the Moon and Jupiter; future plans may include lunar resource extraction.
• Cost Engineering:
  • First principles: the main constraint is the raw material used; targeting small, mass-producible, affordable units is key ([113:58]).

9. Cultural & Manufacturing Mindset ([116:35], [120:34])

• Rapid Prototyping:
  • Helion has built seven end-to-end prototypes, each iteration about learning and manufacturability, named with a sense of humor (Redmond, Starbucks cup sizes).
  • “The faster you can build a thing, the faster you can learn... The irony is that by focusing on manufacturing... you actually get to do science faster.” (Kirtley, [116:35])
• Builder Culture:
  • Scrappiness is an asset (“We spent a lot of time on eBay... you just got a pump in two weeks instead of nine months.” [125:01]).
  • Technician-heavy company (about 50% technicians, 50% scientists) to emphasize hands-on iterative building ([128:06]).
  • Vertically integrated: manufacturing critical components in-house.

10. Deployment, Timeline, and Scaling ([131:18], [141:32], [145:22])

• First Commercial Plant:
  • Deal with Microsoft aims to deliver grid-connected fusion power by 2028.
  • “It is daily that we think about that deadline.” (Kirtley, [132:19])
• Scaling Up:
  • The goal is a “gigafactory” for fusion plants—eventually rolling out one generator per day or more ([145:25]).
• Integration with AI & Data Centers:
  • Fusion power complements the explosive energy demand of AI.
  • Pulsed systems can deliver direct DC power, opening new designs for energy and compute integration ([140:00]).
• A Vision for Civilization:
  • Fusion as enabling factor for “Kardashev Type 1” civilization, cheap desalination, vertical farming, and more ([148:46]).
  • “The universe is powered by fusion. Humans need to be harnessing this for our society...” (Kirtley, [144:11])

Notable Quotes & Memorable Moments

On Fusion’s Role in History & the Cosmos:

• “For all of human history we've been limited by energy scarcity... If someone is able to solve commercial fusion, we would enter a new era of energy abundance.” (Fridman, [00:00])
• "Fusion is fundamentally safe. And that's really a key requirement of any industrial system: it turns itself off and is safe." (Kirtley, [26:59])

On Nuclear Proliferation and Geopolitics:

• "Fusion power plants can't be used to make nuclear weapons... please, please go develop fusion power plants absolutely as fast as possible. The world needs this." (Kirtley, [34:14] and [37:58])
• “Everyone has deuterium... no one can control the fuel, no one can cut a pipeline. That just cannot happen with fusion.” (Kirtley, [40:03])

On the Pace of Innovation:

• "At Helion, we've built seven systems... The first six were a series of prototypes... The most successful was the Inductive Plasmoid accelerator, the IPA." (Kirtley, [120:34])
• “You can go to eBay and get three turbo pumps right now. Bring them in, test them. Maybe only one works, but you got it in two weeks instead of nine months.” (Kirtley, [125:01])

On AI, Scaling & the Future:

• "There's not a lot of technologies that can get us to Kardashev Type 1 just from the point of view of the fuel. But if, as some research says, there's a hundred million to a billion years of fusion fuel on the Earth, we have room to go." (Kirtley, [148:46])
• “I think about how does that work with nature? If you have power—energy dense—why can't you build a building where you're actually growing (food) inside? Why not 500 feet? ...We can coexist in a way that's energy dense and rich.” (Kirtley, [151:13])

On the Sense of Wonder:

• “I'm continuously in awe that it works... the more I learned... the right balance between the electromagnetic force and the strong force... Each of the leaves on a tree, each cell, each atom’s quantum substructure... all the pieces come together.” (Kirtley, [163:06])
• “The first time it comes online and flashes pink and you see that fusion glow, it's awe-inspiring.” (Kirtley, [136:02])

Timestamps for Important Segments

| Segment | Description | Timestamp | |---------|-------------|-----------| | Fusion vs Fission Basics | Laying out the essential physics and cosmic context | [11:43] – [21:05] | | Fuel Abundance & Storage | On deuterium, heavy water, and resource scale | [18:23] – [20:39] | | Fusion Safety Analysis | Why fusion plants are inherently safe | [40:47] – [43:52] | | Proliferation Risks | Weapons, politics, and expert consensus | [34:14] – [38:38] | | Fusion Approaches | Tokamak, stellarator, FRC, & Helion’s methodology | [47:28] – [69:35] | | High-Beta Plasma & Stability | The crux of Helion’s design | [72:34] – [80:20] | | Achieving High Temperatures | Speed, temperature, and electronics | [83:41] – [87:21] | | Diagnostics & Real-Time Control | Fiber optics, assembly, and Fortran | [87:21] – [91:09] | | Simulation & AI | Magno-hydrodynamics, particle codes, reinforcement learning | [91:09] – [97:15] | | Fusion Scaling & Direct Electricity | The B³·⁷⁷ law, efficiency, extraction | [97:15] – [108:13] | | Cost Engineering & Manufacturing | Size, iteration, eBay hacks, builder culture | [113:58] – [129:27] | | Commercial Deployment Plans | Helion’s timeline, Microsoft partnership | [131:18] – [133:28] | | Scaling for Civilization | Fusion gigafactories, integration with AI/data centers, Kardashev scale | [141:32] – [148:46] | | Philosophical Reflections | Fermi paradox, beauty in physics, awe in technology | [156:34] – [164:10] |

Conclusion

Kirtley and Fridman’s conversation delivers both the technical depth and the human, even playful, perspective necessary to appreciate the daunting but exhilarating challenge of commercial fusion. From hands-on prototyping and eBay-scrounging, to leveraging the most advanced computer modeling and AI, Helion and the emerging fusion ecosystem are translating the physics that power the stars into a scalable, manufacturable future for humanity—one iterated prototype and tight deadline at a time.

Final Thought:

“We choose to do these things not because they are easy, but because they are hard.”
— John F. Kennedy (quoted by Fridman, [164:38])