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Piston-Powered Nuclear Fusion
katarn writes "General Fusion is a startup proposing they can create commercially viable fusion using acoustic shock waves, triggered by 220 precisely controlled pneumatic pistons. Their approach is based on a US Naval research concept called 'Linus' and old research done by General Atomics. They feel we now have the high-speed, digital processing capable of pulling off this feat, where decades ago the technology was not available. I think we can hold off on the 'vaporware' claims for a bit; everyone is aware of the horrible track record for turning fusion concepts into reality, but they don't claim to be the first with the idea or that there are not substantial challenges in the way. If nothing else, it is a fascinating concept."
Los Alamos National Laboratory has further details on this type of fusion, and longtime LANL researcher Ronald Kirkpatrick did an external assessment (PDF) of General Fusion's plans. Popular Science had a lengthy story about the company a while back. The reason they're back in the headlines now is that they've secured enough funding to begin work on a prototype reactor.
There's been some modest interest in actively stabilized fusion for a while, but this is the first mechanical scheme.
The basic problem with fusion reactors is that the plasmas aren't stable. Most work to date involves trying to come up with some geometry that produces an inherently stable plasma. So far, nothing works, although some geometries almost work. But it's not that hard to build a small machine that has an unstable plasma. The original Stellerator, in 1951, did that.
The instabilities occur on the order of milliseconds, not microseconds or nanoseconds. That's slow enough that some kind of active stabilization scheme to nudge the instabilities back in line might work. Something with a large number of sensors and actuators. But I'd been expecting electrostatic deflection plates or magnets, not physical pistons.
Perhaps if the D-T reactor does really well they can redesign it to handle a fuel composed of hydrogen ions (protons, in other words) and Boron-11 ions. The products of this reaction are helium-4 ions, which are not radioactive and do not induce radioactivity in their containment vessel if they are captured electrically. Electrical capture also avoids the losses associated with converting heat to electricity.
I really hope General Fusion gets this to work, but if I had any money, my money would be on EMC2 Corp, which is working on inertial electrostatic fusion. This or this should get you started on a search for more information.
They're not going to stabilize the plasma at all, if I understand this right (IANANP). It's a pulse fusion model: put your hydrogen in the middle, surround with a working fluid that they refer to as "liquid metal" (made of lead + lithium), fire off pistons to make a pressure wave in the liquid metal and make a burst of fusion in the middle, generating heat. This makes the molten lead even hotter, and it's circulated through a heat exchanger. The cool part, I thought, was that the lead also absorbs radiation so the casing and equipment doesn't fall apart after a few months because the neutron flux made it brittle. That's a neat trick.
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As someone who works for a startup, I cannot empathize how WRONG you are. Almost every aspect of what we do to bring our particular product to market is new and needs to be thoughtfully researched and developed. It isn't easy but the potential rewards make it worthwhile. We spend a lot of time 'proving' our ideas with prototypes to provide proof that we know what we are doing and that the risk for investors is reduced.
The huge yield of Castle Bravo was more due to the unexpected reactions with lithium-7. It wasn't expected to react, but it does capture neutrons, then decays into tritium + a neutron. The tritium quickly fuses with deuterium and releases yet more neutrons. Much of the yield was from the uranium casing, but the reason was the extra high energy neutron flux from the lithium-7. And the secondary in a TU design has the fusion squeezed from both the spark plug detonation (plus a lot of neutrons) and the ablative pressure, on the tamper, from the primary. I'm going to guess that they used a larger amount of the lithium-deuteride because it was only partially enriched. Which meant a lots of unexpected extra energy and neutrons from the lithium-7.
Mr. Burns: [over the hotline] Oh, meltdown. It's one of these annoying buzzwords. We prefer to call it an unrequested fission surplus.