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A comment on DARPA wants to bypass the thermal middleman in nuclear power systems. Parent comment

Re:DARPA wants to bypass the thermal middleman in nuclear po... by sigmoid10 on Friday August 09, 2024 @06:35PM (#41205923)
Fusion is infinitely harder for this than fission. No company has demonstrated stable fusion with a positive net energy gain. Most of these startups are borderline scams for milking gullible VCs. Helion in particular has been around for more than a decade and was supposed to reach break even in 2023. They haven't even achieved a fully stable D-D reaction so far. The biggest thing it has achieved is siphoning tons of money from OpenAI's investors because of some questionable actions by Sam Altman.
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Re:DARPA wants to bypass the thermal middleman in nuclear po... by fallingknife on Friday August 09, 2024 @08:19PM (#41206468)
What do you know that all those investors don't that lets you so confidently call this a borderline scam?
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Re:DARPA wants to bypass the thermal middleman in nuclear po... by sigmoid10 on Tuesday August 13, 2024 @10:25AM (#41235794)
I have seen this whole scheme play out more than once by now. Helion is not the first fusion startup. Not by a long shot. It's just one of those who gathered media attention (and even that was not due to their science but to OpenAI's business practices). If you're an investor, you're welcome to hire me as an adviser and I'll tell you exactly where and how they are being delusional or outright dishonest. But most investors get hitched on nice pitch decks and certain keywords or names.
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Re:DARPA wants to bypass the thermal middleman in nuclear po... by Intralexical on Friday August 09, 2024 @07:20PM (#41206203)
Fusion overall is harder than fission.

Is the direct energy capture part also harder for glowy fusion gas than scary fission rocks?

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Re:DARPA wants to bypass the thermal middleman in nuclear po... by thayne on Friday August 09, 2024 @08:13PM (#41206449)
I think in a Deutritium-Tritium fusion reaction a lot the energy is in the neutron. And since neutrons are neutral you can't really directly convert that into electrical energy.
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Re:DARPA wants to bypass the thermal middleman in nuclear po... by DennisP on Friday August 09, 2024 @09:02PM (#41206622)
Yep, for D-T 80% of the energy is in neutrons. Helion is using D-D/D-He3, and for that it's about 5% in neutrons, and most of the rest in fast-moving charged particles.

So they have a simple way to extract electricity directly. They squeeze the plasma with a magnetic field from a copper coil, then there's an explosion of charged particles, which pushes back against the magnetic field and causes electricity to flow in the coil.

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Re:DARPA wants to bypass the thermal middleman in nuclear po... by sigmoid10 on Monday August 12, 2024 @02:41AM (#41221715)
D-D (which they are going for right now) is still 50% neutrons. D-He3 is the only aneutronic reaction, but it has tons of other issues.
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Re:DARPA wants to bypass the thermal middleman in nuclear po... by DennisP on Monday August 12, 2024 @06:30PM (#41230093)
As I said, the combined reaction generates 5% of its energy as neutron radiation. The reason it's only 5% is that D-He3 is a much more energetic reaction.

The main issue with D-He3 is that it's more difficult.

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Re:DARPA wants to bypass the thermal middleman in nuclear po... by sigmoid10 on Tuesday August 13, 2024 @10:23AM (#41235762)
That's what I said. But all things equal, D-D is definitely not the best path for direct energy production because of the vast amount of neutrons.
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Re:DARPA wants to bypass the thermal middleman in nuclear po... by selectodude on Friday August 09, 2024 @07:26PM (#41206237)
I think the concepts are the same but the execution (heat up water with plasma) is still a work in progress.
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Re:DARPA wants to bypass the thermal middleman in nuclear po... by Intralexical on Friday August 09, 2024 @07:30PM (#41206260)
That's the "thermal middleman" part they're trying to cut out.

By analogy, compare Concentrated Solar Power versus Photovoltaics.

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Re:DARPA wants to bypass the thermal middleman in nuclear po... by DennisP on Friday August 09, 2024 @08:26PM (#41206490)
It's a pulsed reactor by design, it's not supposed to create a "fully stable" reaction.

They're actually pretty much on schedule, once you account for the several years it took them to get the necessary funding.

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Re:DARPA wants to bypass the thermal middleman in nuclear po... by sigmoid10 on Monday August 12, 2024 @02:38AM (#41221694)
All of those experiments say they are "on schedule" for whatever schedule they made up for this year. If you have been following this for as long as I have, you'll know that these statements are worth nothing.
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Re:DARPA wants to bypass the thermal middleman in nuclear po... by DennisP on Tuesday August 13, 2024 @05:49AM (#41233883)
You're the one who referenced their earlier published schedule, which said they were "supposed to reach break even in 2023." They had a couple years of delay in funding after making that statement.
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Re:DARPA wants to bypass the thermal middleman in nuclear po... by sigmoid10 on Tuesday August 13, 2024 @10:21AM (#41235752)
All the more reason not to trust any schedule laid out by them this time.
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