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Comment by guimarin | Hacker News Reader

The problem with Fusion has always been that R&D associated with it has no bearing on any first order weapons technology. Sure you might be able to put a reactor on an aircraft carrier, but studying powergeneration from fusion reactions does not yield higher yield!

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The advantages from getting it to work are sufficient on their own merits to not require massive military application. Practical fusion is worth trillions of dollars in the decades after its development. If we get it, all the billions we've poured into it, even down a blind alley, will seem like an underinvestment.

and yet the US has defunded and underfunded new Fusion research related to power generation at every turn for the past 20 years. Pinning our hopes on the ITER boondoggle.

>The problem with Fusion has always been that R&D associated with it has no bearing on any first order weapons technology.

actually i think it is quite opposite - the inertial confinement approaches have from the start been the most promising, and they are relatively easy to miniaturize - thus paving the way for the neutron weapons without fission primary. No first-rate power - who already has nuclear weapons and thus has no real need for new types of neutron weapons - is interested in second-grade players obtaining such weapons bypassing the need for fission primary, as all the hurdles related to fission primary is what provides for non-proliferation.

Thus all the government funded research has been only in non-miniaturizable (as seen decades back) Tokamak and laser confinement. Sandia Z-machine (great inertial confinement approach) could have been burning DT targets at the end of 199x, yet they started to do it only 15 years later (at least officially) - somebody definitely wasn't in a rush :) With tremendous progress in solid state lasers i kind of curious what fate (ie. government funding) is waiting for NIF as upgrading its warehouse size 3% efficient lasers to container size 20-50% efficient solid state would obviously be in order. Yet it doesn't seems it is going to happen - the last monthly NIF's status update was in May 2014 and officially it has stopped ignition experiments and back to material research (simulating plutonium compression in the nukes)

Nit-pick: the problem with the Z-machine fusing D-T is that the D-T reaction kicks out a ton of neutrons. Once you turn a plasma research experiment over to actual fusion, you end up with secondary activation of the machine's core components, thereby turning them into high-level radioactive waste. This stops you tearing it down and poking around inside and reconfiguring it.

This was the fate of the UK's JET experiment at Culham (the Joint European Torus, predecessor to ITER): once they finally bit the bullet and went to actual fusion containment experiments, the "hot" reactor became a lot less accessible for tinkering and reconfiguration. So you don't take that step until you're real sure you don't want to play with your plasma containment experiment any more.

It's hard to blame anyone for that. I don't know how the world would deal with hydrogen bombs that didn't take a huge industrial effort to produce. Probably by blowing each other up until no one could build them anymore.

> and they are relatively easy to miniaturize

Wait, really? How?

while it is obviously a sarcasm, it suggests that there is need to point obvious difference between energy and power and its density. Inertial confinement schemas don't require large energy, they require huge power and power density though. I.e. a few joules in a femtosecond impulse concentrated in a few cubic millimeters volume. Reaching that power and density is just a pure engineering task, there is no hard physical limits preventing it as there are for example on the minimal size of tokamak.

Ok, and I thought I was cynical :-) I'd challenge your assessment that there isn't a weapon here. Look no further than the rail gun which consumes copious amounts of electrical charge, which a fusion reactor could replace rapidly. There are also the laser weapons which have demonstrated that chemical lasers are too fragile for battle. Large arrays of semiconductor lasers though, collimated into a single beam get you there. Also a consumer of lots and lots of electricity.

So one day your cruiser class naval ship starts boiling the ocean around it while it fires of its lasers and rapid fire rail gun.

Since these fusion reactors generate heat, you still need the steam turbine and generator. So the capital cost ($/watt) can't be noticeably less than oil burners. For weapons, fuel cost hardly matters because it's operating for such short periods. So thermal fusion reactors don't enable rail guns.

Not necessarily. See [1] although there are better sources out there. But one of the things that makes fusion much more interesting is that it is theoretically practical to do direct energy conversion. This is much much harder in fission systems as the only thing fission generates is massive amounts of heat, whereas fusion can generate massive amounts of magnetic flux.

[1] https://en.wikipedia.org/wiki/Direct_energy_conversion

The Navy already is investing in fusion research through the Polywell design. Nuclear reactors on ships are big, heavy maintenance intensive, relatively fragile, and require a rather involved port call for refuelling. Any sort of fusion-powered craft would be quite literally floating on its own fuel supply, making it cheaper to operate, safer, and cleaner, which makes the end of life costs for a ship lower.

Or some say the opposite: that the practical development of fusion energy at the NIF and Sandia played a secondary role to weapons research. So they made engineering decisions to probe the limits of fusion physics, rather than making something that works.

I think it's a stretch to ever think there was practical development for energy occurring at those facilities. When you think for 10s about the efficacy of dropping a deuterium pellet every 100ms into a laser chamber that literally needs the lasers to fire 3X orders of magnitude faster than currently possible to sustain a fusion reaction you come to the realization that this was always and only about weapons research.

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