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Y Combinator And Mithril Invest In Helion, A Nuclear Fusion Startup

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Re: Y Combinator And Mithril Invest In Helion, A Nuclear Fusion Startup

#121

Post by aetherson »

sillysaurus3 wrote: post #109
aetherson wrote: post #103

Earlier quoted context omitted.

Regardless of everyone's feelings on whether weapons research is or isn't a good idea, this strikes me as a grossly unlikely application. The problem with direct-fire weapons is not something like "bullets don't do enough damage." It's aiming and range and so forth. A plasma weapon seems unlikely to have good range or good aiming, and if it does not come with a fusion reactor alongside it, it's also kind of hard to s…

Rather than a literal plasma gun, I think they were just saying the risk is that the team will pivot into weapons research. But no one has thus far explained why weapons research would be anything but a positive thing. Yes, using weapons is unfortunate. The decision to ever use a weapon should be made with the utmost discretion. But when it comes time to use a weapon, it seems hard to argue against having the most ef…

And what I'm saying is that regardless of the ethics of it, why should we regard it as in any way plausible that this company would pivot into weapons research?

By a huge margin, the most plausible military application of anything this company develops is "a fusion reactor on an aircraft carrier."

And I say that as someone who regards it as deeply unlikely that this company will create any major step towards a fusion reactor.

Re: Y Combinator And Mithril Invest In Helion, A Nuclear Fusion Startup

#122

Post by rdl »

Arnor wrote: post #82
sillysaurus3 wrote: post #59

Earlier quoted context omitted.

The risk of #3 is that they don't create fusion but they do develop a machine that can emit streams of hot plasma which is then turned into the Navy's weapon of choice for close weapons support on carrier battle groups. Why is that a risk? I'd like to live in a country with that technology, because otherwise other countries will have it and we won't.

It's a risk to the investment firms because it would deplete an upside they get from this investment: the halo effect.

Depending on the military application, it might still have a halo effect.

Great skill in manipulating magnetic fields would probably be useful for: MRI. Detecting landmines and UXO in a field from a UAV or otherwise safe distance. Detecting submarines, including those by terrorists or rogue states transporting NBC weapons.

While those are military applications, they're fairly unalloyedly positive.

Even the hypothetical plasma rifle isn't necessarily a bad thing; if a plasma rifle allows rich countries like US, Japan, etc. to overmatch poor countries and thus prevent war, that's kind of a plus.

Re: Y Combinator And Mithril Invest In Helion, A Nuclear Fusion Startup

#123

Post by omegant »

dkirtley wrote: post #31
iLoch wrote: post #13

Can someone with some knowledge on nuclear energy explain to me how this solution varies from say, General Fusion ( http://www.generalfusion.com )? They're a company more local to me, and while these companies are looking to accomplish the same thing, their approaches are wildly different.

Both GF and us (Helion) are attempting to dramatically shrink the size and cost of fusion reactors. We are doing that by compressing a fusion plasma repeatedly to generate energy, rather than trying to heat and confine it for long periods. The main difference is that Helion uses high field pulsed magnets to compress the plasma, GF uses pistons to generate liquid metal shocks.

Are you guys thinking in a crowdfounding campaign, I'll give money to help projects like yours.

Re: Y Combinator And Mithril Invest In Helion, A Nuclear Fusion Startup

#124

Post by GFK_of_xmaspast »

BugBrother wrote: post #89
soperj wrote: post #78

Earlier quoted context omitted.

I'll never understand being able to kill someone in a humane way(through acts of war). You're killing someone.

How about if we put it like this? When a democracy has a war with a dictatorship it is similar to when the police defends civilians from violence. (So this don't get into a shouting match: Check "democratic peace theory". I am aware of that the police can misuse their position. A democracy often also do cynical realpolitik when it isn't its voters that gets harmed.) Edit: You might want to do the distinction of a jun…

Go back to Ferguson.

Re: Y Combinator And Mithril Invest In Helion, A Nuclear Fusion Startup

#125

Post by scythe »

sbierwagen wrote: post #66
scythe wrote: post #63

Earlier quoted context omitted.

>D-He3 fusion produces less neutron flux than D-T, but it's hardly aneutronic-- otherwise they couldn't breed 3He from it. You can't "breed" 3He; you have to breed tritium, which decays to He3 with a half-life of 12 years. D-3He reactors do produce some neutrons, roughly 1% of the flux of D-T, and almost entirely from D-D side-reactions. Actually, a big problem with D-3He as of today is the lack of neutrons -- since…

You can't "breed" 3He; you have to breed tritium, which decays to He3 with a half-life of 12 years. Huh, I didn't know that. Helion directly claim they've "developed [a] complete self-supplied 3He fuel cycle", though. How did they manage that? Are they just massaging the truth, by saying that warehousing the tritium exhaust for a decade, then putting the 3He back in the reactor, still counts as a closed fuel cycle? I…

>Helion directly claim they've "developed [a] complete self-supplied 3He fuel cycle", though. How did they manage that?

I have no idea.

The D-3He reaction is: D + 3He >> p + 4He + 18 MeV. The D-D side-reaction is D + D >> n + 3He. Maybe they're recovering 3He from the side-reaction? But D-D is harder to ignite than D-3He.

This would hardly be aneutronic (you'd have one neutron per two nuclear collisions, instead of roughly per 100 with exogenous 3He), but it does provide a way of making 3He. I should stress that I am only guessing.

>Are there any running fusion experiments that use internal boron carbide cladding to shield the vacuum chamber walls?

Germany's new stellarator, Wendelstein 7-X: http://www.sciencedirect.com/science/article/pii/S0022311504...

[1] http://www.sciencedirect.com/science/article/pii/S0920379697...

Actually, ITER uses beryllium[1]. This has the same high cross-section and low propensity to create dangerous radionuclides as B4C, but is expensive and toxic. It is, however, much easier to make things out of, because it is just a metal. Older projects use tungsten, which does create dangerous radionuclides (181W and 185W). I was mostly aware of research re: B4C, but had been ignorant of beryllium.

So I should have said "modern fusion reactors generally use first-wall materials like boron carbide and beryllium, which do not become radioactive when irradiated". In practice, it's not worth holding up experiments on containment to make safe walls (ITER isn't built to last). In any case, the question of irradiated reactor walls is slowly becoming a solved problem.

http://en.wikipedia.org/wiki/Plasma-facing_material

http://en.wikipedia.org/wiki/International_Fusion_Materials_...

Re: Y Combinator And Mithril Invest In Helion, A Nuclear Fusion Startup

#126

Post by Htsthbjig »

marcell wrote: post #60

Can someone explain why this team is confident that they can build a commercially viable reactor in 3 years? Conventional wisdom is that nuclear fusion is "decades away". What does this team know that others don't?

Because it is so small that you could actually control most of the variables.

E.g they generate a magnetic field and they recover the energy from the same magnetic elements generating electricity instead of having to add a completely independent turbine generator with all the heat and radiation problems associated with it.

Even if they don't reach the goal, they could discover something useful.

Re: Y Combinator And Mithril Invest In Helion, A Nuclear Fusion Startup

#127

Post by cpihl »

curtis wrote: post #91
cpihl wrote: post #76

Earlier quoted context omitted.

Close but with some important differences. We've tried that approach and it has some interesting potential applications but, when it comes to building a power plant that has to last decades, we think the engineering is just too difficult. Instead of pushing on a liner that then pushes on the plasma, we directly push on the plasma with magnetic field. The engineering, while still difficult, is much easier to tackle.

Is this a purely magnetic approach? I recall recently reading about a MagLIF variant that used lasers for pre-heating.

It is. We use electromagnets to make the plasmas, move them, and finally compress them all without moving parts, just magnetic field.

Re: Y Combinator And Mithril Invest In Helion, A Nuclear Fusion Startup

#128

Post by todd8 »

This whole discussion about weapons seems strange. It's true that the words "nuclear fusion" appear in the article, but my reading of the article doesn't make me feel that this research will lead to some terrible, existential risk to mankind.

For comparison, consider robotics, drones, nanotechnology, and AI. I am fascinated by these subjects (and, apparently, so are many other HN readers), but I have some concerns that these non-nuclear technologies may end up having very negative consequences. Yet these high tech areas, with which I would guess the HN readers have a better understanding than fusion, don't engender such negative reactions here.

Re: Y Combinator And Mithril Invest In Helion, A Nuclear Fusion Startup

#129

Post by DennisP »

scythe wrote: post #125
sbierwagen wrote: post #66

Earlier quoted context omitted.

You can't "breed" 3He; you have to breed tritium, which decays to He3 with a half-life of 12 years. Huh, I didn't know that. Helion directly claim they've "developed [a] complete self-supplied 3He fuel cycle", though. How did they manage that? Are they just massaging the truth, by saying that warehousing the tritium exhaust for a decade, then putting the 3He back in the reactor, still counts as a closed fuel cycle? I…

>Helion directly claim they've "developed [a] complete self-supplied 3He fuel cycle", though. How did they manage that? I have no idea. The D-3He reaction is: D + 3He >> p + 4He + 18 MeV. The D-D side-reaction is D + D >> n + 3He. Maybe they're recovering 3He from the side-reaction? But D-D is harder to ignite than D-3He. This would hardly be aneutronic (you'd have one neutron per two nuclear collisions, instead of r…

According to wikipedia D-D is the second easiest reaction behind D-T. Half the reactions produce 3He directly. The other half produce a proton plus tritium, which decays to 3He with a 12-year half-life.

You'll get some D-T from the tritium you produced, but the pulsed reaction probably helps a lot.

"Assuming complete removal of tritium and recycling of 3He, only 6% of the fusion energy is carried by neutrons."

http://en.wikipedia.org/wiki/Fusion_power#Deuterium.2C_deute...

Re: Y Combinator And Mithril Invest In Helion, A Nuclear Fusion Startup

#130

Post by [deleted] »

sbierwagen wrote: post #81
dkirtley wrote: post #74

Earlier quoted context omitted.

Great reply. The wiki also has a long discussion about Helium 3. http://en.wikipedia.org/wiki/Helium-3 Fusion produces neutrons either in the first or secondary reactions, but there are ways to minimize the amount of them and their energy (and damage/radioactivity)to where you don't generate "nuclear waste". There is an interesting continuum of fusion reactions from pure D-D (which produces little energy, but lots of…

He3 is never added? How long can a reactor run without supplying He3? (This thread is having a hard time settling on a single isotope notation.)

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