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.

Actively stabilized fusion

[Animats]

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.

p11B

[pitterpatter]

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 [blogspot.com] or this [emc2fusion.org] should get you started on a search for more information.

Interesting...

[kabz]

I wonder if this is related to the suspected fusion that occurs during ultrasound induced cavitation.

Pulse fusion, it looks like...

[FooAtWFU]

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.

Re:p11B

[FooAtWFU]

If you read the site, you'd see one of the tricks they have up their sleeve to deal with the radioactivity problem: they surround the actual fusion process with a working fluid of molten lead (and lithium) which not only transmits the shockwave from the pistons, but also absorbs neutrons. If the reactor does well, they shouldn't have to change the fuel at all.

Re:p11B

[WalksOnDirt]

Oops, the half life of 205Pb is long enough to make it a problem. There won't be a lot of it, though, as 204Pb is only 1.4% of natural lead.

Re:If the government did research that proved

[jpmorgan]

The vast majority of fusion research funds from US government flow through the Department of Energy. The senior guys at the DoE have a few pet approaches to fusion, and 99.9% of the funding goes into those. Innovative, small scale, low cost approaches like this, or IEC polywell fusion are left begging to the Navy for funds, but the Navy has far less money to spend on nuclear research than the DoE.

Re:There is reason to be concerned.

[j.boulton]

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.

Re:Fantastic Fiction

[amRadioHed]

Was real? My office is just down the street from them. Sure they aren't doing that cool Project Orion stuff anymore but they're still here.

Re:Pulse fusion, it looks like...

[dkf]

So it's a perpetual motion machine?

What on earth gave you that impression? Converting lithium to tritium leaves less lithium behind, and the energy would be coming from rearranging nucleons. No perpetual motion there at all.

Re:Why why why...

[maxume]

Because it works.

Re:So its a hydrogen bomb

[Anonymous Coward]

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.

Re:Why why why...

[michael_cain]

Because it works.

To expand on that point, because it's inexpensive, it uses common materials, and it scales. The problem of "I have an object here that produces lots of heat energy, I'd like to convert that heat to useful work, please" is harder than it sounds.

Re:Actively stabilized fusion

[Animats]

The TOTAL confinement time looks like it'll be measured in microseconds at most on this thing, no way is there time for active control of the plasma during a shot like that.

I see that. So what do they want all the compute power for? I'd assumed I was reading an oversimplified version, and all the compute power was to actively stabilize something. If they just need a simultaneous push, they don't need compute power. I'm missing something.

There's work on active stabilization. See "Active-Feedback Control of the Magnetic Boundary for Magnetohydrodynamic Stabilization of a Fusion Plasma" [aip.org]. That's a 2006 paper on a scheme involving 192 active feedback coils to stabilize a plasma. There's other work like that, and hope that one of the designs that's almost stable might be nudged into stability with active control.

Re:Actively stabilized fusion

[deglr6328]

I don't understand why they need the computing power either.

here's work on active stabilization. See "Active-Feedback Control of the Magnetic Boundary for Magnetohydrodynamic Stabilization of a Fusion Plasma" [aip.org]. That's a 2006 paper on a scheme involving 192 active feedback coils to stabilize a plasma. There's other work like that, and hope that one of the designs that's almost stable might be nudged into stability with active control.

Yes but that work was done on the reverse field pinch device called RFX-mod ( http://www.igi.cnr.it/rfxmod2009/ [igi.cnr.it] ). It's a tokamak-like magnetic confinement device so it probably has shot times measured in the multi-second range. Plenty of time for active stabilization but way different from this new MTF approach.