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Roger Arnold's picture
Director Silverthorn Institute

Roger Arnold is a former software engineer and systems architect. He studied physics, math, and chemistry at Michigan State University's Honors College. After graduation, he worked in...

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  • Jul 27, 2021

I wouldn't normally post a shared link to an article about fusion energy. I see little chance that fusion will become a practical energy resource anytime soon, and articles about it are distracting.  But I'm making an exception in this case. The approach that Helion Energy is taking is different than anything I've seen before. I think it has genuine potential.

An interesting side note -- and another reason for posting this -- is that Helion is expecting production 3He on Earth. I.e., they're not expecting it to be mined on the moon from lunar regolith.

A lot of articles about lunar mining for 3He have been showing up lately. I don't want to discount that possibility altogether. The solar wind has deposited a lot of 3He in the lunar regolith, and its value to a nascent fusion energy industry would run to $millions per kg. That's high enough to justify importing it from the moon -- once Musk's reusable Starships begin flying. But importing it from the moon is not the only option. 3He is the stable decay product of 3H (tritium). Tritium can be produced via neutron activation of 6Li. It has a radioactive half-life of 12 years; half of any store of tritium will decay to 3He in 12 years. Neutron activation of 6Li, however, is only practical at scale inside fission reactors.

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Roger Arnold's picture
Roger Arnold on Jul 27, 2021

Oops. A not-so-minor clarification / correction. The PNAS article I linked to was not specifically about Helion Energy. It was a more general article about the field-reversed configuration (FRC) for dense plasma confinement, as explored by a group led by Samuel Cohen at the Princeton Plasma Physics Laboratory. The article does go on to talk about Helion Energy. Helion is working to commercialize a fusion reactor using the same principles of FRC plasmas studied by Cohen's group. Here's a paragraph I should have included:

If and when Cohen does reach his fusion energy milestone, he will likely have company. His device is just one of a family of small, alternative reactor projects designed to exploit a phenomenon known as the field-reversed configuration (FRC): a dense mass of ionized plasma that holds itself together something like a smoke ring and that could allow researchers to achieve fusion conditions with comparatively little effort. Among the members of this family are some of the best-known fusion upstarts: firms such as TAE Technologies (formerly TriAlpha Energy) in Foothill Ranch, California, and Helion Energy in Redmond, Washington.

Cohen's group is apparently more focused on use of D-3He fusion for high performance interplanetary spacecraft, not for large-scale terrestrial power. They're not planning to produce 3He.

And speaking of production of 3He, I should have read the FAQs on Helion's web site before I posted. There's another way to produce 3He besides neutron activation of 6Li. At the plasma conditions required for D-3He fusion, there will also be a degree D-D fusion. D-D fusion events produce, with equal probability, either a tritium nucleus + high energy proton, or a 3He nucleus + high energy neutron. If plasma temperature and density are sustained for any appreciable length of time, the tritium and 3He products of D-D fusion events will be consumed in subsequent D-T or D-3He events. But if the plasma is expanded and cooled very quickly, some of the residue of D-D fusion will remain. That's partly how Helion is aiming to produce helium-3 fuel. I'm sure neutron activation of 6Li will still be part of it, since that's the most effective way to capture the high energy neutron radiation produced by half of the D-D fusion events.

Matt Chester's picture
Matt Chester on Jul 27, 2021

Thanks for the article and for the follow up comment, Roger. I'm grateful for your insights on where fusion is / isn't a major topic of focus, but also I can't help but smile at how we've long been looking at metaphorical space races to perhaps see which country would come up with the type of moonshot energy technologies that would change the industry, only to see that perhaps it's a literal space race that will unlock that door!

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