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 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 subreddit post by

pmgoodbeer on this, the preferred pronunciation

of the latter in the US is nuclear fission, like

vision. And in the UK and other countries is nuclear fission, like

mission. I prefer the nuclear fission pronunciation because

America. So today's nuclear power plants

use nuclear fission. They 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

something goes wrong, the reactor simply stops. And there's

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, 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 podcast episodes.

This is a Lex Fridman 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? 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 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.

We also talk about the strong nuclear force that holds the

atomic nuclei together as one of the fundamental forces involved in

fusion. But that mass defect, E=MC², 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 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 sub-atomic 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=MC², 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 fission

or are fissile and break apart and release energy.

I think about and I look at that process 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 that

whole stellar process is something that inspires us 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

- Okay, so there's a million things I want to say. First, zooming out to the biggest possible

picture, if you look across hundreds of millions, billions of

years, and all the, my opinion, alien

civilizations that are out there, they're going to be powered

likely by fusion. So our advanced intelligent civilization is powered by fusion in that

the sun is our power plant.

Then the other thing is the physics. Again, very basic, but you said E equals MC squared

a couple times. Can you explain this equation?

- E=MC squared is a fundamental relationship that a patent clerk, Einstein, discovered and unlocked

an entire new realm of physics and engineering and has shown us

engineering and has shown us

atomic physics, what happens inside the nucleus, and unlocked our understanding of the universe

and paved the way for many of the physics advancements that came after.

That we think about mass as these particles. But in reality, at the same time, they're energy,

and there's a direct quantitative relationship between how much energy is in all of that mass.

And in fact, all of the energy that is released, even by atomic physics, certainly in atomic

reactions, is E=MC squared. I think most people have heard of and are used to this.

But also in chemistry and in chemical bonds, there is a change in mass. When you take a

those chemical bonds, there is a change in mass. When you take a

hydrogen and an oxygen and you burn them and you combine them into water, there's a change in mass.

Now, that change per atom and per molecule is actually so small that it's extremely hard to

molecule is actually so small that it's extremely hard to

measure, but it's still there. That's the energy that is released, and you can quantify that.

We use units of electron volts as a unit of what is the energy in atomic processes or chemical

processes.

- Can you also just speak to the different fuels that you mentioned, both on the fusion and

fission side?

...fission side? So uranium, plutonium for the fission, and then hydrogen isotopes for the fusion?

- So for fission, uranium and plutonium, we don't make those nuclei. Those, right now for humanity,

make those nuclei. Those, right now, for humanity,

those have been made in the primordial universe through super-supernova and Big Bang

and the initial formation of the universe where matter was created. And so we dig those up.

We dig up uranium, plutonium out of the ground. And in fact, most plutonium we make from

uranium, and we can talk about how to enrich uranium if we want to go down that road.

But that's how we get those molecules and nuclei. For fusion materials, hydrogenic species, or

hydrogens are primordial in the universe. Also, only the most common things that are in

primordial in the universe. Also only the most common things

the universe. The suns and stars are made up of hydrogens and heliums, and so the vast

majority of atoms in the universe still are hydrogen.

- So the basic fuel for fission is already in the ground, and then the basic fuel

for fusion is everywhere.

- Is everywhere, and we particularly use a type of hydrogen

called deuterium, which is a heavier isotope

of hydrogen. Hydrogen is typically one proton and one

electron, atomic mass of one. Deuterium is an atomic mass of

two, which is a proton, which is a charged particle, and it has a neutron in

its nucleus, which is an uncharged particle. And so that's deuterium.

As the fuel now, deuterium is also found in all water on Earth, in the

water I'm drinking right now. It's in my body. It's in Coca-Cola. It's everywhere.

And it's safe and clean and one of those fundamental particles that was

born in the cosmos, and 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.

- And how is that stored mostly?

- Mostly that's just in water. Mostly it's a mix of, we

call this actually heavy water, where you have normal water that you're

used to. We talk about and you learn in school, is H2O, where

there's two hydrogens and oxygen in a nucleus in the

molecule. And deuterium, or heavy water, is

D2O, two deuteriums and an oxygen. In reality,

it's actually an interesting mix where you have some

HDO, so a mix of hydrogen and deuterium. You also have other hydrogen

but also in chemistry and in chemical bonds, that in those chemical bonds, there is a change in mass.

- ...fission side? So uranium, plutonium for the fission, and then hydrogen isotopes for the fusion? In terms of fuel, is that correct to say?

- That's correct to say at today's power level. I think what's interesting is

the idea that as we deploy the same power source that powers the

universe here on Earth as humans, can we do

more? Can we have access to much more electricity, and much more

energy and do really interesting things with that? And still there's

large amounts, millions and millions of years of power even at

much higher output power levels for humanity.

- Yeah, so the moment we start running out of

hydrogen and helium, that means we're doing some pretty incredible

things with our technology. And then that technology is

probably going to allow us to propagate out into the universe and then discover other sources.

Because you can also get it on other planets.

Whatever planets have water, it looks more and more likely like a lot of

them do. What an incredible future, just out into the cosmos, nuclear power plants

everywhere. Okay, so to linger on some of the technical stuff, you said

strong nuclear force. So how exactly is the energy

created? So how does the E=MC squared, the M go to the E infusion?

- So in fusion, you take these lightweight isotopes like

hydrogen and deuterium, and as you combine them and get them

closer and closer together, some really interesting fundamental physics happens.

So first these atomic nuclei are charged. They have an electric

these atomic nuclei are charged. They have an electric

charge, and they like charges repel. And I think everybody is

familiar with that, where you take two positive charges, and you try to push them

together, and the electromagnetic force between them repels them. 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. And temperature really is kinetic energy. It's

motion, it's velocity. So that these particles are moving so

fast that even though they're coming together and there's this repulsive