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Comment by dnautics | Hacker News Reader

I still don't understand what the game plan is for laser-induced fusion. How do you collect the energy? By contrast: I have a vague idea of how one might do it for magnetic confinement, and I even remember one magnetically confined system where there was direct electrical potential generated and extracted from the system.

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As far as I know, this kind of system is most useful for simulating nuclear explosions while remaining compliant with the Nuclear Test Ban Treaty of 1963.

It's a Department of Energy project, and DoE is primarily focused on nuclear weapons. It is undoubtedly used for nuclear weapons research. Discussion of the technology for use in any kind of power plant is just PR.

There are higher-energy reactions, like p+B11, that generate very few neutrons (it's dubbed "aneutronic" for the main reaction, if you can get there cleanly), and instead yield high energy charged (alpha) particles and photons. These could maybe be directly converted to electrical energy by a number of proposed mechanisms[2].

Highly challenging, but if possible, a very nice energy source, and we're finally out of the steam age!

[1] https://en.wikipedia.org/wiki/Aneutronic_fusion#Boron

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

There is no such game plan. It is a giveaway to military contractors, corporate welfare.

Magnetically confined D-He3 or H-B fusion could, in principle, be viable, because there is no detour through collecting hot neutrons, but is harder to achieve.

It is research for nuclear stockpile maintenance, which depending on how you view nuclear weapons could be a bad thing but is absolutely not a giveaway to the MIC. You'll notice all the main authors of the paper work at national labs which are funded directly by the federal government.

You are aware, are you not, that the national labs in question are operated by military contractors, literally under contract? And that the people nominally working for these labs are actually, literally, employees of those contractors?

You propose a distinction where there is no difference.

Absolutely none. The laser itself is absurdly inefficient, and you can't really collect the energy efficiently. It will essentially never be efficient.

It's most realistic application would be for space travel.

It gets a lot of funding as a sort of backdoor for nuclear weapons testing.

In the U.S., nuclear weapons get a couple orders of magnitude more government money than fusion, and nobody blinks an eye. So it seems more likely that weapons work is a backdoor to get some fusion research done.

Hardly. This kind of plasma physics is nearly orthogonal to research that puts carbon-neutral electricity on the grid.

To the best of my knowledge, there is no design for a laser induced fusion power plant. However, at the current stage all fusion experiments are precisely that, experiments and laser induced fusion is currently the only way to generate a plasma similar to the ones that would exist in a future fusion plant, so this is to study plasma properties, not a prototype for a power plant.

(And of course, that is also similar to the plasmas in a H-bomb, so there is a weapons aspect, but it's not like that we don't already know that H-bombs work.)

Simple, heat something up and run a turbine. With D-T (the easiest fuel), the energy output is 80% neutron radiation so a heat cycle is your only option regardless of reactor design.

To avoid a turbine, you need a fuel whose output is mainly fast-moving charged particles.

For anything remotely resembling a practical reactor, the cooling system for the reactor vessel would have a boatload of heat to get rid of. So maybe the very hot coolant from there gets pumped through a steam generator, which then feeds a steam turbine, which drives a generator.

Or, you might leave a (carefully-shaped) hole in one side of your reactor, and call it a nuclear rocket.

I like the rocket idea.

There are overwhelmingly better fusion rocket ideas that take no detour through hot neutrons and heat.

Good old nuclear salt water rockets: https://www.npl.washington.edu/av/altvw56.html

Just don't point the exhaust at anything inhabited.

This was my "holy shit" read of the day.

There are two ways to do a nuclear rocket. The "clean" way, closed loop. And the "dirty" way. Open loop.

Closed loop is actually not all that different from using a reactor as a generator. But instead of using your cooling system to power a turbine via a head exchanger, you use it to heat a reaction mass such as H2.

Open loop is closer to what you describe. Instead of indirectly heating your reaction mass, you run it directly through the hot reactor. It's simpler and lighter but your exhaust is extremely radioactive. Your reaction mass essentially doubles as the cooling system. Another downside to this approach is you cant run the reactor without making thrust. So lights out if you are coasting I guess.

This is just fusion research. No one plans on using this as a practical way to set up stable fusion. Still you need to know what happens practically and not just on paper.

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