Prepare yourselves everybody, I’m about to quote the greatest superhero movie ever made: “The power of the Sun… in the palm of my hand.” Unfortunately for Otto Octavius, and spoiler alert anyone who hasn’t seen Spider-Man 2, his invention wound up at the bottom of the Hudson River.

But two decades later, scientists are still chasing  the nuclear fusion dream. They’re not building machines that house a miniature Sun, though.

Oh no. Real fusion reactors are way more complicated. And if you want something that can supply a steady stream of nuclear energy to the masses, you have to make it big.

This is ITER, the largest nuclear fusion reactor in the world. Or at least it will be when  engineers finish building it, and scientists finally turn it on. But here’s another spoiler alert: it’s going to be about as useless as Doc Ock’s creation.

And that’s okay. [intro jingle] As the name implies, nuclear fusion happens when two atoms get so close they wind up fusing together. And for atoms lighter than iron, this winds up releasing a ton of energy.. It’s kind of the opposite of fission, which is what people are usually talking about when the phrase “nuclear energy” comes up.

That’s what all of Earth’s current nuclear plants are doing… cracking atoms that are heavier than iron into smaller bits in order to release energy.. And sure, fission can provide a ton of power… But kilo for kilo, it’s peanuts compared to what you can get with fusion. Hence the allure to both real scientists trying to save the world’s energy needs… and supervillians with robot arms.

But there’s a reason this  kind of nuclear technology seems stuck in science fiction. Getting atoms to fuse together is, like, really hard, which means you need to pump a lot of energy into the system. And there’s no point in having a fusion power plant that can’t get more energy out than you put in.

But scientists are slowly making headway, especially in the past few years. Back in 2022, researchers at the National Ignition Facility, or NIF, managed to achieve what’s known as ignition. That means their fusion reaction produced at least as much energy as they put in for the fusion to happen in the first place.

I do have to put an asterisk on that, though, which I’ll get to, later. Now, these NIF researchers hadn’t quite harnessed “the power of the Sun,” because they didn’t use the  same kind of nuclear fuel that the Sun does. Instead of your standard just-one-proton-in-a-nucleus hydrogen, they used a mix of deuterium and tritium.

These are both heavy forms of hydrogen. Each deuterium nucleus has a proton and a neutron, and each tritium has a proton and two neutrons. And together, they’re the most commonly used fuel for modern fusion research.

That’s because fusing  deuterium and tritium together requires the lowest temperature, so it’s the easiest one to get popping off. But the fuel source isn’t the only way NIF’s reactor isn’t like a mini Sun. Humanity doesn’t have the mass of an entire star to gravitationally smush hydrogen nuclei close enough to get fusion going, so we have to get our extreme pressures and temperatures elsewhere.

In NIF’s case, we use a technique called inertial confinement fusion, or ICF. As the name implies, you want to create a situation where your nuclear fuel gets  confined by its own inertia. And to do that, the NIF team puts a little capsule filled with deuterium and tritium into the middle of a very large chamber, and then fires 192 laser beams at it until the fuel reaches star-like temperatures.

The capsule violently implodes, triggering a fusion reaction that races through the capsule faster than the atoms inside it can get out of the way. That’s the inertia part. The deuterium and tritium atoms are, roughly speaking, at rest before the implosion, so they want to stay at rest.

Ultimately, that means you get a bunch of teeny-tiny nuclear explosions, which everyone crosses their fingers to see if they can collectively release more energy than was put in. And in 2022, that was the story you may have heard in the news. Maybe you even heard more than one kind of jargon being used: NIF hadn’t just “achieved ignition”, it had also “achieved a Q greater than one!” That’s because in the nuclear world, Q is basically the ratio of the energy you get out of reaction to the energy that was put into it… asterisk.

But what a lot of those news sites didn’t clarify was that Q doesn’t account for all of the energy involved in a fusion reaction. In NIF’s case, it’s just the energy directly provided by the lasers to kickstart the reaction. And when you account for the energy NIF had to pull from the grid to power the lasers… the amount of energy the team got out was only like 1% of the energy they put in.

But not only is NIF nowhere near producing net positive energy, it’s also nowhere near producing enough energy to power, well, anything. I mean, that’ll happen when your fuel cell is the size of a pencil eraser… So across the world, other scientists are investigating an entirely different technique to achieve a self-sustaining fusion reaction… one capable of powering itself so you don’t have to keep pumping energy into it, but can keep getting energy out. Thanks to EnergySage, the online home energy marketplace, for supporting this SciShow video!

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So you can go solar with confidence, even if you rent your home. You can start powering the  planet with clean, affordable, and reliable energy at EnergySage.com or at the link in the description below. Now back to the show. to the other major form of fusion experimentation: magnetic confinement.

Instead of creating a bunch of little explosions, magnetic confinement creates a concentrated blob of super hot plasma. And by super, I mean something like 100 million Kelvin… ten times hotter than the core of the Sun. There’s no solid material on Earth that can hold something that hot.

But since all the particles in a plasma have an electric charge, you contain it without touching it by using very powerful magnets. And back in the 1950s, some incredibly whimsical Russians named one kind of magnetic confinement reactor a “toroidal chamber with magnetic coils.” Eventually, that got shortened to what everyone calls this kind of nuclear fusion tech: A tokamak. And here’s the kicker, building a bigger tokamak doesn’t just mean you can fill it with more nuclear fuel.

It also gets you more efficient fusion. In other words, it increases that aforementioned Q value… at least in theory. So the largest fusion reactor in the world is one of these tokamaks.

But I’m not talking about ITER. Remember, it’s still under construction. [optional: This episode is a road  trip through fusion reactor research,   and we’ll get there when we get there.] I’m talking about the JT-60SA , which was first activated in October of 2023. Located in Naka, Japan, this record-holding tokamak clocks in at 15.5 meters tall and 13.5 meters wide.

It was designed to constrain  140 cubic meters of plasma at a temperature of 200 million degrees Celsius for up to 100 seconds Now, unlike NIF’s reactor, the JT-60SA doesn’t fuse  deuterium and tritium together. Tritium is both expensive and radioactive. So even though your regular, run-of-the-mill hydrogen is way harder to fuse, that’s what these researchers  have started working with.

Eventually, they’ll do some tests with deuterium. But all of this research is really meant to be a stepping stone to more important projects… …Including, yes, the project that comes up when you search what the world’s largest fusion reactor is. ITER stands for International Thermonuclear Experimental Reactor.

It also means “journey” or “the way” in Latin… But I like to think it stands for drama. Because hoo boy has this project’s history been steeped in drama. ITER originated back in the ReaganGorbachëv days.

By which I mean then-General Secretary Gorbachëv proposed to President Reagan that the USSR and USA should collaborate on  developing fusion energy tech and not, you know, use it to blow each other up. But that agreement was made in 1985. Four decades and over 20 billion dollars ago.

And for all you space nerds out there, unfortunately, it seems the project is pulling from the James Webb Space Telescope playbook. Between 2006 and 2015, the start-up date was roughly a decade away. Then, ITER’s project managers finally settled on 2025 as the deadline.

But time crept forward… and forward... And while we were putting this episode together, ITER pushed the dates back once more. They hope to turn the reactor on for an initial round of plasma research in 2034, but won’t actually start fusing deuterium and tritium together until 2039.

But all you space nerds know that JWST was worth the wait. So the question is, will ITER be just as revolutionary? Well when it’s finished, it’ll be capable of holding about 840 cubic meters of plasma.

Or six times more plasma than  the current record holder. And with that much plasma, scientists are hoping ITER will become the first fusion reactor to be self-sustaining. See, whatever your fuel source, and however much you have of it, one of the main products you’re going to get out of a fusion reaction is heat.

And as much as it’s hard to deal with, heat is also a good thing. Because it’s what lets the reaction… react. So with 840 cubic meters of fuel, ITER should create enough heat to keep that fuel at that fusion-promoting 100 million Kelvin, without any outside boost.

Of course, scientists first have to turn the reactor on and see what Q can they get. The current record from NIF is about 1.54. But ITER’s rather lofty goal is a whopping 10.

That means researchers expect ITER to release 10 times more energy than what they put into the plasma. Whether or not they can get more energy out than what they need to fully power the reactor? Well, we’ll have to see.

But after ITER makes all that energy, what are we going to do with it? A whole lotta nothing, at least practically speaking. ITER is not being built to generate electricity.

The neutrons created as the deuterium and tritium fuse together will slam into the inner reactor shielding and heat things up… …and the excess heat will just be vented into  the environment instead of, oh I don’t know, boiling water and using the steam to turn a turbine like all of our  existing nuclear power plants. So as massive a project as ITER is… both in terms of physical scale and budget… it’s ultimately just an experiment to get things moving in the right direction. It’ll be up to the next  generation of fusion reactors to test how we can transition to generators that’ll power our homes and whatnot.

According to some proposals, one or more of these future reactors could be up to 50% larger than ITER. But anyone trying to one-up the world’s largest fusion reactor will quickly run into some  serious practical limits. For one, if you plan on sticking with deuteriumtritium reactions, you’ve got to worry about the whole  tritium-is-very-rare-and-expensive thing.

And for another, you have to account for the extra infrastructure it takes to operate not just a giant fusion reactor, but one hooked up to a power grid. The bigger they are, the more complicated and more  expensive that’s going to be. So ITER itself isn’t going to save the world.

But this isn’t the first time we’ve spent a bunch of time, money, and effort building a big, fancy machine that’s basically just meant to figure out how the universe works. Look at JWST. Look at the particle accelerators at CERN.

ITER will help us understand just how realistic a fusion-powered future is. But scientists? Maybe don’t build an experiment that you have to contain by plugging a set of artificially  intelligent metal tentacles into your brainstem. [ OUTRO ]