Nuclear Con-fusion

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I’ve been seeing a lot of headlines like this over the last few days:

Germany takes a major step towards nuclear fusion!

Nuclear Fusion could soon become reality in Germany!

And now

China’s nuclear fusion machine just smashed Germany’s hydrogen plasma record!

From the way the news is being reported, in the click-baiting headlines at least, you’d think that we’d all be switching to clean cheap nuclear energy in a matter of days. This is, of course, not the case.

So what has happened?

The German fusion experiment, Wendelstein 7X Stellarator, has not only won the Science Burrito award for coolest experiment name, it has also completed its second successful plasma generation experiment. In the first they made a helium plasma, in this second, a hydrogen plasma.

This is getting confusing already. Let’s explain this a bit. Cast you mind back to our first jaunt into science. You recall the atom? A bunch on negatively charged electrons orbiting a positively charged nucleus? Well, normally, the positive and negative charges in an atom balance each other out. What this makes is neutral atoms, atoms with no total charge. In a plasma, the electrons and nuclei separate and you end up with charged matter. The electrons separate and make negatively charged gas of electrons, and the nuclei a cloud of positive charge. When the electrons and nuclei come back together, or recombine, they produce light. This is essentially what a flame is.

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The problem with plasmas is, they don’t last. This particular plasma needs a lot of heat to be maintained (literally millions of degrees). The slightest loss of that heat and the plasma dies. So the scientists in Germany have to make sure the plasma is isolated from anything that might leech its heat, including the cold, hard walls of the reactor itself. Luckily, as you’ve just learned, the plasma is charged, and charged particles can be pushed around by magnetic fields. So they use giant supermagnets to hold the plasma in place.

In a normal bar magnet, the fields goes from North to South, as we have all seen with the classic iron filings experiment.

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This is great! But it doesn’t really contain anything. All the field lines run alone the outside of the magnet (I suppose you could say that only the magnet itself is ‘inside’ the field). But, if you take a lot of these magnets and arrange them in a circle, like so:

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Now we have a donut shape (also known as a toroid), with an inside and an outside. It still doesn’t work very well as a cage though. It’s not closed off. So what we do is, we take a whole bunch of these rings and we make another, bigger ring (in the Stellarator, we also add a bit of a twist, like a Möbius strip, or you can just make another plain ring, to make a tokomak reactor). And voila!

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We now have a suitable cage for our plasma. The magnetic fields twist and turn back on each other making a cavity for the plasma. You can think of it as like making a big, invisible, spiralling, circling track around which the plasma can flow.

Ok. Great. Why? Well, once matter is in this plasma form, it is free to collide and recombine into new forms, new atoms, with larger nuclei and more electrons. So, the lightest element possible, hydrogen, which contains one electron and one proton, can become helium, which has two protons and two electrons (and two neutrons, which is cool, as the positive proton and the negative electron need to fuse together to make neutral neutrons). Making these new atoms produces energy, and that’s what makes it a reactor, the production of energy, which we can turn into useful power.

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But here’s the catch. It takes a lot of energy to get one of these plasmas up and running. And I mean A LOT. In fact, a 1.8 megawatt laser pulse was required (that’s about as much energy as output by over 2000 microwave ovens) and this plasma lasted only a few thousandths of a second.

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Clearly, that’s not long enough for a useful power station to function. And the reactor takes a lot more power to make the plasma than the plasma gives out. It’s like having a machine to chop fire wood, but you have burn more fire wood to run it than it could ever chop. Pretty useless, ultimately. In fact, this particular experiment was never designed to tip the balance and produce more energy than was put into it. It was only ever meant to prove that this particular design of reactor can indeed create plasmas. And in this, it has succeeded beautifully, which is fantastic.

I want to stress that at this point. What they have achieved in brilliant, and very, very important. If we can crack nuclear fusion, get a net output of energy (more energy out than in) over sustained periods, it would be the greatest scientific achievement of our lifetimes, possibly of all time. And we are getting closer all the time. The National Ignition Facility in the US has just about tipped the energy output balance, so it can be done! And eventually the French might finish their own reactor, ITER.

So here’s what to be excited about: Any of this is possible at all, and the idea of a working nuclear fusion reactor is not just science-fiction, but has a very good chance of one day becoming science-fact.

And here’s what to be aware of: This isn’t happening any time soon, no matter what the click bait articles say. Fusion has been said to be a decade or two away since the 1920s (it is actually a joke in the physics community that fusion will always be 20 years away, it has been predicted so often). But it really, really could happen. Who knows, perhaps in around 20 years or so?

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