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Two Fusion Researchers Explain The Tokamak Reactor That I Want To Be Hurled Into

Rendering of SPARC, a compact, high-field, DT burning tokamak, currently under design by a team from the Massachusetts Institute of Technology and Commonwealth Fusion Systems. Its mission is to create and confine a plasma that produces net fusion energy.
Illustration: T. Henderson, CFS/MIT-PSFC/Wikimedia Commons

Scientists at the Plasma Science and Fusion Center at the Massachusetts Institute of Technology are working on a project called SPARC, which if they are successful could deliver the world’s first fully operational thermonuclear fusion reactor. Using massive superconducting magnets, a cocktail of hydrogen isotopes, and various other complex-sounding science things, what they’ll be producing at the core of a tennis-court-sized, donut-like device called a tokamak is a compact cloud of unfathomably hot plasma, suspended in a vacuum, fusing atoms and pumping out incredible energy. They will have made a little star.

As a right-thinking person isolated on the miserable crust of our ruined, dystopian world, my wish, upon learning of this and similar projects—which scale established tokamak science to vastly more powerful and potentially commercially viable levels—was to one day present myself at the doorway of the SPARC reactor and be physically thrown into the God Cloud at its core, so that I may be destroyed. In order to assess the feasibility of this wish, and perhaps to schedule an appointment, I made contact with two brilliant fusion-knowers currently working at MIT on plasma science-type stuff. Though they could not speak for the SPARC project in any official capacity, they were happy to share their knowledge of plasma science and fusion, and to brainstorm some ideas for how man-made plasma clouds may be used to zap me into the afterlife.

Sara Ferry is a postdoctoral associate at the Plasma Science and Fusion Center, where she develops nuclear materials for advanced reactor concepts. She is also a fan of the various dreaded New England sports teams. Erica Salazar is a fourth-year PhD student and doctoral candidate in the nuclear science engineering department at MIT, where her research involves superconducting magnets in fusion energy applications. Their confidence in their combined ability to lift me from the floor and heave me in any direction, much less into the radiant plasma core of a mighty tokamak, is not super high, but they do know a lot about plasma and fusion, and are remarkably good at talking about these things so that mere idiot bloggers can follow along. We spoke Friday morning. The interview has been lightly edited for brevity and clarity.

I was reading that plasma may be one of the most abundant forms of matter in the universe. But where is it? Where is the plasma?

Sara Ferry: So, stars are an obvious answer. There are entire divisions in plasma science that focus not at all on fusion energy and just focus on the astrophysical side of things. Nebulae contain plasma, and stars obviously use fusion as their power source. But when we look at our world, at Earth, we’re not really seeing plasmas much, except for lightning bolts, which would be an example of like a natural plasma that you would see.

Erica Salazar: Fluorescent lightbulbs, too, have plasma inside. That’s a fun thing we don’t really think of much.

SF: Right. Our everyday sensory experience is not really encountering plasmas. But if you were to total up all of the matter types in the universe, it would actually be mostly that.

But I can’t, like, make plasma from the comfort of my kitchen, right?

SF: You can put a fork in the microwave.

Wait! And that would be making plasma?

SF: Or the grapes thing?

ES: Yeah, that’s absolutely right. Imagine a lightning bolt, like Sara mentioned, there’s plasma involved with that. So if you have any sort of arcing, you have plasmas.

Wait, what was this about grapes?

[several seconds of silence]

SF: Erica, do you remember this thing from the internet?

ES: I do. I think what it is is if you cut a grape in half and then put the two halves close together, you can form a little arc between them.

SF: All plasma is is ionization. In this case, it’s ionizing air molecules. Instead of having just neutral particles, you’re stripping some of the electrons off of them and giving them a charge. And then you start to see that really interesting electric behavior. When things are charged, they’re going to interact differently than they would if they’re just sort of neutral. So yeah, you can make your own little tokamak research center in your kitchen, I guess, if you want to get really ambitious and kill some grapes.

[Ed. note: It is not a great idea to use your microwave for plasma creation experiments. It can be dangerous, and you should not do it, even though it looks pretty bitchin’.]

ES: I think Sara did make a really interesting point about how, because you’re stripping electrons away, you can kind of control and play with the plasma, with magnetic fields. That’s kind of a fun, really neat aspect about plasmas in general.

And that’s what these reactors really are, right? It’s playing with plasma using some really big magnets.

SF: Exactly. And because inside the reactor the plasma is so hot, there’s really no material that would just be able to contain it. The magnets also let you kind of keep the plasma away from components and might give you a chance to actually build something, like a structure, that would be able to contain something this insanely hot and energetic.

You will note that I have not actually used the word yet. How are we pronouncing the ah, the thing…

SF: Tokamak! [TOE-ka-mack]

Ah, good, I wasn’t that far off. So, hey, has anyone considered throwing some grapes in there and seeing if that helps?

SF: I mean, there was one point where I was trying to figure out how many electric eels you would need from the New England aquarium to generate a sufficiently strong magnetic field. We do stupid thought experiments frequently, because it’s funny. But, no, we haven’t done it with the grapes yet. But we will keep it in mind for future experiments.

I was reading that for fusion you need the right cocktail of hydrogen isotopes. What does that mean? What’s going on there?

SF: Yeah, so there’s a few different ways that you can get a fusion reaction that produces energy. The lighter isotopes, when they fuse together, that reaction … I’m trying to think of a good way to explain this. That is a more stable form, for them to be fused together, and it releases energy. It’s sort of the opposite of what happens in a fission reaction, when a heavier, unstable element splits apart, and then those split-apart forms are more stable, and then that releases energy. Both fusion and fission are just ways of releasing energy. And then we can capture that energy and do useful things with it. In fusion, you’re doing it with these lighter elements. And then there are certain different reactions. The one that we kind of focus on, when it comes to energy applications, is the deuterium-tritium reaction. The reason for that is just that that is the reaction that is the easiest to make happen. 

There are other fusion reactions that will release energy, but they require a lot more energy to get the fusion reaction happening, which means they’re just that much more difficult to create. And if your ultimate goal is to work for something that can be an energy source, you want to give yourself an easier starting point. You don’t want to make it 100 times more difficult at the beginning. So that’s why most of the reactor concepts that you’ll see when you read about people pursuing fusion energy will be focused on deuterium-tritium.

ES: One thing that helps and is kind of fun to think about is that deuterium is a heavy hydrogen isotope that is abundant in seawater. Or at least you can find it in seawater, a lot. It’s fun to think that a fuel source for this is just seawater. And you can create tritium via the processes of a fusion power plant.

Cool, so with seawater and grapes you’re most of the way there.

SF: Yeah, we went down to the ocean and chucked a bunch of grapes into the seawater and nothing happened, so now we’ve moved on to this other research.

ES: Hey, gotta start somewhere.

There’s this Joint European Torus (JET), I read they produced 16 megawatts of fusion energy using 24 megawatts of thermal power, which is the closest to breakeven of any tokamak so far. I assume SPARC is going to kick the shit out of JET, yeah?

SF: No, we don’t want to think about it like that! These are all super important experiments. There’s all different fusion research happening all over the world. The community as a whole is very tied into what everybody else is doing, because you’re all pursuing a common goal. But like with any type of technology, first of all, you’re going to want to be pursuing multiple different approaches. JET is also a research device. So, they’re not trying to just prototype some sort of power-producing device, but what they’re doing there is they’re learning more about how do we control the process, how do you get a more efficient reactor design. Like with any of these devices, their goal is not necessarily to achieve a huge amount of power so much as it is that they have these other really, really important scientific missions that help further what we know about fusion and plasma and magnets and all manner of things. There’s a ton of these experiments throughout the world.

ES: JET is a really neat device, and a lot of what we’ve learned about plasmas and fusion energy comes from that, in addition to many other fusion devices.

This non-competitive attitude will not go over well on a sports website, guys.

SF: [laughing] Maybe we would be that way if we were decades into making fusion power and having it on the grid, then maybe we’d be doing that. It’s a big technical challenge, we have a vested interest—everybody in the community has a vested interest in having as many people working on it as possible, regardless of where they’re working, or what reactor they’re working on.

ES: Maybe our “opponent” isn’t other projects, we’re trying to beat nature itself. It’s never been done before! Let’s just break that.

SF: It’s gonna take more than just, you know, one set of people, and everything builds on everything else. It’s really expensive. It’s very difficult research. It’s a win-win for everybody when other groups are doing well and are doing important work. And we publish our work and spend a lot of time interacting with other scientists. There’s nothing to really be gained from being overly insular. Like, it’s not a huge community. It’s not like every other person you meet on the street is a fusion engineer. These other devices have accomplished absolutely huge and really important things in the field. And there’s also a lot of crossover, like people have worked on one experiment and then moved to another. It’s a relatively open community, not like little islands.

This is maybe a dumb question, but it is important to my desire to be hurled into a tokamak.

SF: [lying] There are no dumb questions!

Well, I was in Arizona years ago, and I stayed at this mountaintop place run by this guy, a former astronaut. He had a humongous telescope and one night he gave us a tour of the skies and it was amazing, the stars individually are really incredible to just stare at. Anyway, it occurred to me today that you’re gonna have a beautiful little star inside your tokamak, but you will not be able to look at it! Or will you be able to look at it?

SF: Well, we have really sophisticated diagnostics. And this is also its whole own area of research. It’s not my area of research. Erica, you might have more experience on this. But there are entire teams at every fusion research center that specifically work on novel ways to understand and measure what’s going on in the plasma when it’s on. And you also need to control it, you want to have a lot of good information about how it’s performing. There’s all sorts of ways to measure things other than just by looking at them. And also, like, really, what would looking at it tell you? You’d be like, Wow, bright, cool.

Yes, that is what I would say.

ES: I would also add, too, that when you look at the stars, you’re not even seeing everything! We can only see what’s in the visible light spectrum. There’s so much more, you know, stuff that’s going on, and we can’t even see it. So, to see or not see the visible spectrum of what’s going on inside the tokamak itself, there’s a lot of stuff that we can still see using other instrumentation and diagnostics. The same way telescopes can help us see what we don’t see with the naked eye up in space, too. 

But won’t you be heartbroken to not see the little star with your own eyes? I would be.

SF: I may be wrong about this, but I think if you look up videos of people doing plasma shots at tokamaks, you can see the inside of the torus lighting up. [Ed. note: The torus is the donut-like body of the tokamak.] You’d get that visual impact of being like, “yeah, it’s happening!” But really what most of the technicians are going to be looking at is the numbers on the screen that might look kind of boring but are really a lot more exciting and interesting.

So, uhh, if you aligned the magnets on the tokamak just so, could you make a giant lightsaber out of the tokamak? And smite the moon with it?

[a very, very long period of silence]

SF: Well it wouldn’t be a tokamak, right? Because the tokamak is a closed donut shape.

So we’d have to come up with a different name for it?

SF: We’d need to build a really long tube, I guess? 

ES: It won’t look like a lightsaber, but you could make something that, in a sense, is a lightsaber-type shape. It would look sort of like a lightsaber?

SF: The better option would probably be to make a tokamak that could create a huge amount of power that would then power your lightsaber situation.

Hmm. I had envisioned using the plasma itself for the striking surface. So that’s tough to pull off, huh?

SF: You would need really, really big magnets. Like, I think more volume than we even have in the Earth as a whole. I don’t know, I’m sure someone could do this calculation. One of the intrepid commenters on the Defector website can probably figure it out.

Nah, they’re mostly lawyers, I don’t think they’d be much help.

SF: They’ll have opinions.

Yeah! I mentioned in my tokamak blog the whole breakeven problem in my own dumb way and I had this commenter guy say, “What about such-and-such law of physics.”

SF: And you’re like, whatever.

Knock it off, lawyer! But, like, what is the deal with the breakeven thing, so that I can explain it better next time?

ES: Yeah, sure. So, basically, there’s different ways to have a look at it, but first I’m going to look at the thing that I really care about, the thing that drives the energy, the plasma itself. It does take some energy to actually get the plasma going, and to make sure it remains stable. But then we can also extract energy out of it, or measure the power density of the plasma. So you want to be able to see, is the plasma itself producing in a sense more energy than the amount of energy it takes for us to maintain or control it? That’s when we say we’re having a net energy gain, in essence.

You’re refining the isotope cocktail, the mechanical structure of the tokamak, and the power sources that you’re pumping into the plasma? Is that daunting, trying to gain a watt of fusion energy here and knock off a watt of energy usage there?

SF: It is daunting. It’s a big engineering challenge. A key breakthrough that has come up is much more powerful magnets that can be more powerful in a smaller amount of space with less auxiliary equipment around them, supporting the magnets. That’s made it a lot more achievable. The cost of these large experiments tends to scale with just the plain old size of the machine. So by just being able to make it smaller, right away, you’ve now decreased your cost and the amount of time it takes to build it.

ES: Something I want to add is, yes, we’re able to make it smaller. But the thing, too, is we’re using much higher magnetic fields with new types of magnets and that higher field can make a big change in your power density. It’s very complex, there’s a lot of things going on: plasma density, plasma temperature, and then confinement time. It’s a very complex system, where the plasma itself also has its own mechanisms. There’s a lot of instabilities that plasmas can have, and that’s what many of the different devices help us to understand. What are the best conditions? Or what type of plasmas do we want, to avoid certain issues? It’s not just “let’s get higher fields,” but that is a very big factor in where we are.

SF: You’ll have these big huge teams and these expensive devices that are looking at these really complex things in an experimental way. And so I think that gives some insight into why we haven’t had fusion power reactors. Just because it is a really, really complicated problem. Erica and I each work on our own little segments, so we can speak sort of generally about things, but that’s also why I always say, there really aren’t dumb questions. Like, this is a complex problem. There are plenty of things that we are effectively like lay people when it comes to certain aspects of the machine, and then vice versa for those other teams. It’s really a big team effort to get these things working and then to learn as much as you can from them while you’re building them, and in communication with other research teams around the world.

So, what kinds of things are you gonna fire into the plasma to make it hot?

SF: Erica?

ES: Hmm. I don’t 100 percent know what the plans are for SPARC. I think some papers have just come out recently.

SF: There’s different ways to do it, like some people are using certain radio frequency waves that are, you know, energizing. This is so not my field, I don’t want to say something wrong and have a million people coming after me on Twitter.

ES: Something I do know about is one of the magnets acts as something that helps heat up the plasma, in a way. So you’re not physically injecting anything but the reason why you’re doing that is usually to help, you know, energize the plasma. There’s a certain type of magnet that drives a current in the plasma. It acts as a transformer, essentially. It’s the same thing as a typical transformer, if anyone is familiar with that. You have a magnet, or solenoid, on the inside, that varies its current and magnetic field, which drives a current through the plasma and helps heat it up.

SF: Erica, neutral particle beams, is that also a heating mechanism?

ES: I think it helps with the momentum, is my understanding.

SF: That’s what I think, too. There’s a lot of really interesting techniques that people are pursuing. Some of them are really well-established, and some of them are cutting-edge research. There’s, again, another reason why all these devices are so important, because you need experimental facilities to test and learn about these things. But there’s all sorts of research into, for example, maintaining the plasma’s temperature, or improving its stability, being able to control its performance and make it do what you want to do. This is not a dumb question for us, this is really spot-on with the type of stuff that people are working on. Not so much me and Erica, but other people.

I want the answer to that question to just be lasers. I picture someone firing a laser gun into the cloud and it going “woom woom woom.”

SF: You could propose it! It could be on Chris Thompson’s Science Blog, a little sub-blog on Defector.

[Ed. note: Per a followup email from Sara: “We are in fact going to fire lasers into the plasma cloud! But it will be for diagnostics, not for heating up the plasma. As an example, we can use lasers to study and measure the plasma temperature.”]

OK. We will skip over the question of who would win in a lightsaber battle between the SPARC tokamak and the ITER tokamak.

SF: That sounds really fun! But it would be more like nerds nerding out instead of somebody wanting to win.

ES: I think you would have most of the teams down for a Star Wars lightsaber battle. Sign me up! 

SF: Believe it or not, we are pretty nerdy. I know that might be hard to believe.

Could a person who so desired be thrown into the tokamak? Alternately, could a person “accidentally” stumble into the tokamak, so that they are joined with the plasma? In a beautiful cosmic bonding?

SF: OK, that’s a good question. Um, I feel like the answer is no. Erica, don’t we have pictures of people climbing into the Alcator C-MOD? [Ed. note: This was an experimental tokamak built at MIT that is no longer in use.] Because you needed to get inside there to clean it, and they did research on the inside. So you can fit inside the torus of a larger tokamak.

ES: My answer to your question is, like, unfortunately … so the thing is, fusion energy and plasmas are really hard to maintain. Which is kind of an issue. As soon as you do anything, like open a door—it’s a vacuum in there. As soon as you let the vacuum out the plasma will just fizzle out. In that sense it’s inherently really stable and safe, in the sense that you can’t really melt anything.

So there will not be a super dark five-part miniseries on HBO a few years from now, about the Chernobyl-like disaster at SPARC?

SF: No, no.

ES: I don’t think you’ll be able to mesh with the plasma. But you could hang out! There’s some pretty cool images of people going in and out, cleaning.

SF: The torus is very cool looking, on the inside, but they’re not super comfortable. But if you want to merge with star juice, you’re not really looking for comfort, you’re looking for instant annihilation.

Let’s say someone was in there doing some cleaning and you fired the tokamak up. Would they be in appropriate range for instant annihilation?

ES: I don’t think it would work at all with a human in there. Honestly, if you have too much dust, or dirt, it won’t work.

SF: We’d have to sterilize you to the point that you’re just a cluster of totally neutral … I feel like the process of making it so you could be injected into the plasma would already achieve the annihilation.

But probably a lot less instantaneous and glorious. Like, being scrubbed to the point of annihilation does not sound very wonderful.

SF: We’re getting a business idea. Instead of cremation, we could make people into a few neutral particles that could be shot into a plasma, and help the momentum. We’ll just file that one away.

So we’re probably at least a few years away from figuring out a way to conquer our enemies with tokamak weaponry, but I don’t suppose it could be configured for a short time in such a way that it could be fired into my chest?

SF: You can’t really fire it. Because once the plasma leaves the tokamak, once it’s no longer contained it will just be quenched. So you just sort of wouldn’t have anything, and it would be really sad.

ES: It’s not even at high pressure. So.

What if you lifted the tokamak with a crane and just dropped it on me from a great height?

ES: The infrastructure of the device itself would smash things, sure.