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Skunkworks engineer stumps expert fusion scientists 

Lockheed Martin stirred up science and technology blogs this week with a press release from their "Skunkworks" R&D division. Lockheed-Martin engineer Thomas McGuire reckons his team at Skunkworks will have a full-scale working prototype of the Compact Fusion Reactor ("CFR") within five years, and a commercial product in ten.

McGuire and his team are working toward a 100MW reactor with a footprint of roughly 7 metres by 13 metres. It'll be a factory-built product that can be loaded onto a (somewhat over-width) truck. Aviation World magazine-blog waxed breathless after Lockheed-Martin gave them an exclusive at a big shiny thing that could have been a test rig for the plasma containment system. Their article captures most of the risks and benefits of fusion technology, although they missed what is probably the most exciting bit: If the product lives up to Macguire's claims, it would facilitate a practically unlimited supply of carbon-neutral petrol and diesel at about half the cost of solar fuels.

Daniel Clery at Science magazine scratched under the hood, tracked down McGuire's patents here, here, and here, and then described the plasma containment field in more detail. Clery points out that the structure of McGuire's fusion reactor has some similarity with structures first proposed in the the 1950s.

For me the most interesting aspect of all this is how critics try to naysay McGuire's concept. Several blog-comments worry that McGuire's concept puts superconducting magnets inside the reactor vessel, where the magnets will be bombarded with neutron radiation.

Actually, that's the whole point. Scientists for decades have been putting big thick shielding walls between the magnets and the plasma. McGuire's innovation is to flip the structure inside out. His first patent application describes a cooling system built right into the superconducting magnet. What he's trying to do is transfer energy from the neutron radiation into the coolant, and then pump that energy out where it can be harnessed, for example, by heating water to drive a steam turbine. Interestingly, his patent lists three coolants: liquid helium, liquid nitrogen, and FLiBe. The first two operate at very low temperatures. Liquid liquid nitrogen is cold enough to keep cuprate ("high-temperature") superconductors superconducting. Liquid helium is so cold it is routinely used for cooling conventional superconductors. On the other hand, FLiBe is a molten salt coolant that operates above 500 degrees Celsius! This patent makes it quite clear that at least some of the CFR's superconducting magnets will be fully exposed to neutron radiation. A diagram published with the Aviation Week article backs this up.

Obviously McGuire has convinced the honchos at Lockheed Martin that his idea is worth trying out. It sounds totally crazy to put a cryogenic superconducting magnet that operates at minus 180 degrees Celsius right next to a plasma bubbling away at several hundred million degrees. But it's no more crazy than any other fusion reactor design. When you're talking about temperatures of hundreds of millions of degrees, what's a few hundred one way or the other? There is no way for heat to cross the vacuum between the plasma and the superconducting magnet, except by radiation. Engineers must design the cooling system to get the heat out of the coil fast enough to maintain its operating temperature. Assuming McGuire's 100MW refers to the output of a turbine, and assume each coil cops five percent of the total energy flowing out of the fusion reaction, the cooling system has to handle perhaps 15 MW per coil. That's well within the range of practical cooling systems.

Some commenters worry about what would happen if the superconducting coils "quench", which is basically a kind of melt-down phenomenon. What that tells me is that they don't understand cuprate superconductors - because cuprate superconductors do not quench. If the cooling system fails, they shut down gracefully. Actually, based on what Daniel Clery wrote about McGuire's design, the entire reactor will probably shut itself down with very little trouble.

The CFR concept may not have been possible without the cuprate superconductor technology, with was invented in 1986. Cuprates are easier to keep cool than conventional superconductors, which, I suspect, is important for McGuire's reactor.

The interesting question is how the superconducting coils will cope with neutron radiation. On some materials neutron radiation causes embrittlement and/or transmogrification. I have no idea how this might affect the reactor. It is a good reason for running an extended life test on a small fleet of test reactors before large-scale rollout.

We'll know in about five years if there's anything in the Skunkworks concept. It's competing with another concept dreamed up by University of Washington researchers, and of course, by the gonad-crushingly expensive ITER.

If it works, it will be yet another example of how a simple idea can totally blindside the experts. Scientists are so convinced fusion reactor magnets have to be protected from neutron radiation they reckon McGuire's reactor will actually be the size of a football field. They can't imagine he'd be crazy enough to put the magnets right in there with the plasma. But when you put numbers on it, it doesn't look crazy at all. Just innovative.

Ironically, the CFR appears to depend on cuprate superconductor technology, which itself has the scientists stumped. Almost thirty years after cuprates were invented, scientists have no idea why cuprates superconduct. They just do.

Practical fusion power has been fifty years away for the past seventy years. We'll find out in five years if McGuire's idea can short-circuit the timescale.

 

Kevin Cudby is a Wellington-based Freelance Writer and Parametric Modelling Consultant who loves writing about cool new technology. Email him to discuss your requirements: hello {a} kevincudby.com

Skunkworks engineer stumps expert fusion scientists

 
 
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