Comment by willis936 | Hacker News Reader

Comment by willis936 | Hacker News Reader

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27 comments and not one hit of the word “inertial”! The line about not being thermonuclear and the description of the device in question (a sphere with lasers) points towards an inertial confinement fusion (ICF) device. Most of the fusion research eggs are in the thermonuclear basket, specifically magnetic confinement fusion. It is good to research a diverse set of approaches, but there are more engineering challenges to ICF reactors than there are to MCF reactors. Pulses on the order of 1-2 Hz requires a mechanical system that can cycle out the exhaust and replace the pellet in that time. Going to reactor scales also requires high load thermal cycles. MCF ain’t easy, and brings it’s own engineering challenges. The ones I always hear are things like wall materials and fuel recycling, but these are largely solved or in the process of being solved. The engineering challenge I see as the most difficult for MCF are related to steady state operation. Tokamaks have no way of being steady state. Stellarators do, but now the next problem is wall conditioning. Wall materials outgas in hot plasma. A lot. Like more than the fuel puffed in. The way this is handled in science machines is with glow discharges of various species: plasma just below the temperature to cause wall sputtering, coating the wall with carbon and boron for their absorptive properties, etc. No one’s run a steady state hot plasma before, so no one knows if these will be a non issue in reactors. Keeping the plasma clean may be a challenge to keep the plasma from terminating. Aside from that MCF is ready for prime time. It needs a big reactor for scaling laws to make it energy profitable (and potentially money profitable). We just need some very expensive test reactors to smooth out these issues.

One reason you might not find ‘inertial’ is because the only thing they have in common is a laser.

For ICF, a long-pulse laser is used like a hammer to heat and compress the material to fusion conditions.

This scheme, as far as I can tell, uses the large EM fields of a short-pulse laser to accelerate a ‘beam’ of ions into cold material to induce fusion.

It seems easy to conflate any or all approaches as fringe when no one's done it yet, and especially if there are political and program-$ecurity concerns overriding doing what's best, but some approaches scream magical thinking with unexplained reasoning more than others (like one or more cold fusion proposals in the early 1980's). OTOH, it seems like ICF and tokamak are the officially-sanctioned dogma and all other approaches are discounted automatically.

Q0: Without bias from my opinion, how fringe or potentially legitimate does IEC seem?

Q1: Props to the article's team that they invented some awesome lasers. Is there enough experimental data yet on their novel approach to backup their claims to justify funding a prototype? Would such a team be able to test this on a shoestring budget without spending millions?

IEC is a different fusion scheme.

"Millions" is pretty much a shoestring budget for fusion projects. There is some experimental data, but without actual fusion since the lasers weren't powerful enough yet.

This team didn't invent the lasers. They've been waiting for the lasers to get sufficiently powerful to attempt fusion with them. Those lasers are finally becoming available for researchers to use, so it should be quite inexpensive to test this idea. Worst case, they have to build one for tens of millions, which is comparable to other private fusion projects, but hopefully they can run the experiment on other people's lasers.

Personally, without drawing from rigorous empirical proof that doesn’t exit, I don’t think things like unique IEC approaches are based in fairy tales. Fusion science used to be very tribal and dogma was important. That era has largely passed. Tokamak, stellarator, ps laser, steam machine, whatever. If you can find the money to make it and do the science to show its performance, great. Everyone wants you to do that. This idea of pulling resources away is tricky to navigate, because there is finite resources spent on research and getting any one design to work takes significant effort. That’s why so much is being poured into ITER instead of other promising leads. Humans are ready to see a machine work. It’s painful to get there. It’s not my first pick on a machine. But in order to keep progress moving a real reactor needs to be made of some kind.

The 2015 paper cites 3 other groups with experimental results supporting their claims though.

You misinterpreted what I said. I said that I don't have evidence that inertial electrostatic confinement is not based in fairy tales. As in, they are a reasonable route to explore.

Double negatives are tricky! Now you seem to be saying they probably are based in fairy tales, or at least have no reason to think otherwise. The first time around, you seemed to mean the opposite, which is what you say you actually meant.

There’s been a lot of promising work done on IEC by a startup called EMC2. Their reactor/fusor design is called Polywell.

* https://en.m.wikipedia.org/wiki/Polywell

Not promising at all. Basically, the idea cannot work. EMC2 is defunct, btw.

https://www.reddit.com/r/fusion/comments/dmqgd5/is_the_polyw...

Just a writing critique. I think your post could use paragraph breaks, it's hard to discern the logical structure without breaks.

As an absolute dummie I had to think of ASML where they repeatedly hit molten tin droplets in flight with CO2-lasers, to produce some plasma, to get extreme ultraviolet light out of it. 50.000 times per second. So the part to hit something very small in flight, in a vacuum, precisely and repeatedly exists on an industrial scale already. Though not simple, small and cheap. Should ask Cymer or Trumpf who do this. And forget about all that unnecessary light generating stuff, just ripping out the necessary parts and adapt for their application. And of course harden it against the FUSION happening. Simple, isn't it?

(stupid grin)

Complete layman to this, but are these approaches fundamentally incompatible with one-another, or is it just that each one on its own seems to be “enough” to get a reactor to work? Could you have a reactor that just combines all these confinement approaches at once?

They're not incompatible in the sense that they assume different physics, but they are very different strategies.

The fusion triple product is the go to figure of merit for napkin calculations, it's temperature X confinement time X ion density

MCF strategies go in on maximizing confinement time, while ICF jack up temperature and ion density. This particular ICF approach, (if I'm understanding their paper correctly) is going so high on both that they're leaving the thermal regime behind and doing an honest to glob nuclear chain reaction with having the alpha products prompt other boron nuclei to accelerate up to fusion speed causing more reactions, which is pretty exciting.

Laser inertial confinement causing a nonthermal chain reaction has been making headlines since 2015. I don't think that aspect of this approach is the exciting part. It's how promising their simulated performance improvement is from the use of a laser that causes additional magnetic confinement (I'm a little iffy on how that exactly happens).

In a way, this new design does combine the approaches, since it combines a laser that hits the fuel directly with an extreme magnetic field.

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