Chapter 1: What is nuclear fusion?
The following is a conversation with Dennis White, nuclear physicist at MIT and the director of the MIT Plasma Science and Fusion Center. And now, a quick few second mention of each sponsor. Check them out in the description. It's the best way to support this podcast.
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Chapter 2: How does e=mc^2 relate to energy and mass?
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Chapter 3: What are the differences between fission and fusion?
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Chapter 4: How do nuclear weapons differ from fusion energy?
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What is nuclear fusion?
It's the underlying process that powers the universe. So as the name implies, it fuses together or brings together two different elements, technically nuclei, that come together. And if you can push them together close enough that you can trigger essentially a reaction, what happens is that the element typically changes. So this means that you change from one chemical element to another element.
Underlying what this means is that you change the nuclear structure. This rearrangement through equals MC squared releases large amounts of energy. So fusion is the fusing together of lighter elements into heavier elements. And when you go through it, you say, oh, look, so here are the initial elements, typically hydrogen.
And they had a particular mass, rest mass, which means just the mass with no kinetic energy. And when you look at the product afterwards, it has less rest mass. And so you go, well, how is that possible? Because you have to keep mass. But mass and energy are the same thing, which is what E equals MC squared means.
And the conversion of this comes into kinetic energy, namely energy that you can use in some way. And that's what happens in the center of stars, right? So fusion is literally the reason life is viable in the universe.
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Chapter 5: What engineering challenges are faced in nuclear fusion?
With a giant magnet.
Giant magnet, yeah. So it's basically true.
Engineering is awesome.
There's essentially two ways to create a magnet. So one of them is that we're familiar with, like fridge magnets and so forth. These are so-called permanent magnets. And what it means is that within these, the atoms are arranged in a particular way that it produces, the electrons basically are arranged in a particular way that it produces a permanent magnetic field that is set by the material.
So those have a fundamental limitation how strong they can be, and they also tend to have this circular shape like this. So we don't typically use those. So what we use are so-called electromagnets. And what is this?
It's like, so the other way to make a magnetic field, also go back to your elementary school physics or science class, is that you take a nail and you wrap a copper wire around it and connect it to a battery, then it can pick up iron filings. This is an electromagnet. At its simplest, what it is, it's an electric current which is going in a pattern around and around and around.
And what this does is it produces a magnetic field which goes through it by the laws of electromagnetism. So that's how we make the magnetic field in these configurations. And the key there is that it's not limited by the magnetic property of the material.
The magnetic field amplitude is set by the amount of the geometry of this thing and the amount of electric current that you're putting through. And the more electric current that you put through, the more magnetic field that you get.
The closest one that people maybe see is one of my, one of my favorite skits actually was Super Dave Osborne on, it's probably, probably past years, like in a show called Bizarre. Super Dave Osborne, which is a great comedian called, he was a stunt man.
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Chapter 6: How does magnetic confinement work in fusion reactors?
This is his stunt and Which is pretty hilarious. Anyway, but that thing that picks him up, like how does that work? That's actually not a permanent magnet. It's an electromagnet. And so you can turn, by turning off and on the power supply, it turns off and on the magnetic field. So this means you can pick it up and then when you switch it off, the magnetic field goes away and the car drops.
Okay, so that's what it looks like.
Speaking of giant magnets, MIT and Commonwealth Fusion Systems, CFS, built a very large, high-temperature, superconducting electromagnet that was ramped up to a field strength of 20 Tesla, the most powerful magnetic field of its kind ever created on Earth. Because I enjoy this kind of thing. Can you please tell me about this magnet?
yeah sure oh it was it's fun yeah there's a lot to parse there so maybe uh we so we already explained an electromagnet which in general is what you do is you take electric current and you force it to to follow a pattern of some kind typically like a circular pattern around and around and around around it goes the more time the more current and the more times it goes around the stronger the magnetic field that you make okay
And as I pointed out, it's like really important in magnetic confinement because it is the force that's produced by that magnet. In fact, technically it goes like the magnetic field squared because it's a pressure which is actually being exerted on the plasma to keep it contained.
Just so we know, for magnetic confinement, what is usually the geometry of the magnet?
What are we supposed to imagine? Yeah, so the geometry is typically what you do is you want to produce a magnetic field that loops back on itself. And the reason for this goes down to the nature of the force that I described. which is that there's no containment or force along the direction of the magnetic field. So here's a magnetic field.
In fact, what it's more technically or more graphically what it's doing is that when the plasma is here, here's plasma particles here, here's a magnetic field. What it does is it forces all those, because of this Lorentz force, it makes all of those charged particles execute circular orbits around the magnetic field. Mm-hmm.
And they go around like this, but they stream freely along the magnetic field line. So this is why the nature of the containment is that if you can get that circle smaller and smaller, it stays further away from earth temperature materials. That's why the confinement gets better. But the problem is, is that because it free streams along. So we just have a long straight magnetic field. Okay.
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Chapter 7: What is the significance of the ITER project?
So that's what it looks like. That's what the plasma looks like because that's what the fuel looks like. So then this means is that the electromagnets are configured in such a way that it produces the desired magnetic fields around this. How precise does this have to be? You were probably listening to our conversation with some of my colleagues yesterday.
So it's actually, it depends on the configuration about how you're doing it.
The configuration of the plasma, sorry.
The configuration of the electromagnets and about how you're achieving this requirement. It's fairly precise, but it doesn't have to be, particularly in something like a tokamak, what we do is we produce planar coils, which just mean they're flat, and we situate them. So if you think of a circle like this, What does it produce if you put current through it?
It produces a magnetic field which goes through the circle like this. So, if you align many of them like this, this, this, this, there's things online. You can go see the picture. You keep arranging these around in a circle itself. This forces the magnetic field lines to basically just keep executing around like this. So, you tend to align. That one tends to – well, it requires –
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Chapter 8: What future advancements are anticipated in fusion energy?
good alignment. It's not like insane alignment because you're actually exploiting the symmetry of the situation to help it. There's another kind of configuration of magnetic, of this kind of magnetic confinement called a stellarator, which is, we have these names for historic reasons.
Which is different than a tokamak.
It's different than a tokamak, but it actually works on the same physical principle, that namely, in the end it produces a plasma which loops in magnetic fields, which loop back on themselves as well. But in that case, the totality, basically, the totality of the confining magnetic field is produced by external three-dimensional magnets, so they're twisted.
And it turns out the precision of those is more stringent, yeah.
So are tokamaks by far more popular for research and development currently than stellarators?
Of the concepts which are there, the tokamak is by far the most mature in terms of its...
breadth of performance and um and thinking about how it would be applied in a fusion energy system and the history of this was that many in fact you asked what if we go back to the history of the plasma science and fusion center the history of fusion is that people scientists had started to work on this in the 1950s it was all hush hush and you know cold war and all that kind of stuff
And it's like they realized, holy cow, this is like really hard. Like we actually don't really know like what we're doing in this because everything was at low temperatures. They couldn't get confinement. It was interesting. And then they declassified it. And this is one of the few places that the West and the Soviet Union actually collaborated on was a science.
Even during the Cold War.
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