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Comment by mikeyouse | Hacker News Reader

Here's a related article explaining the most recent test;

https://phys.org/news/2023-02-power-plasma-gigajoule-energy-...

Fusion reactor R&D generally avoids actually starting a fusion reaction unless they're ready to trash the reactor: current reactor designs can only manage D+T fusion, which generates a shitload of neutrons and leaves the reactor interior structures highly radioactive, making modification for further experiments problematic. (No-one is anywhere near achieving the energies needed for aneutronic fusion.)

For example, the JET (Joint European Torus) Tokamak at Culham began operation in 1983 but experiments with tritium only started in 1991; maintenance and upgrades after 1998 relied on a remote handling system as it was no longer safe for human technicians to work inside the reactor containment in shutdown.

https://en.wikipedia.org/wiki/Joint_European_Torus

D-T definitely trashes the reactor, but D-D generates fewer neutrons, so human maintenance is generally OK afterwards. C-Mod at MIT ran this way for a while. You just needed to wear a dose meter.

Small nit if you've never seen it written down, they're 'dosimeters'.

Polywell reactors have been doing D-D fusion since 2005, and measuring very few neutrons produced.

Is polywell dead? So little news.

Seems they concluded that it doesn't scale up. Can't find the source now.

Lots of R&D uses deuterium, the neutron output is lower-energy and a handy diagnostic. Even hobbyists with fusors run on deuterium. Getting net power with deuterium is harder than D-T, but just fusing some deuterium isn't hard.

The same goes for aneutronic fuels, as long as you reach the necessary temperature. Helion for example claims to have achieved a significant amount of D-He3 reactions. LPPFusion has published research saying they've achieved boron fusion temperatures, though not with boron fuel, or the triple product needed for net power from boron. (They're using deuterium though, and getting neutrons.)

ONe of the issues with Fusion: those neutrons mean it isn't the infinite clean energy source: using the reactor makes nuclear waste from the reactor vessel.

Also, even if a viable fusion reaction is produced, it has the same problem as fission reactors: you have to be price competitive with grid storage and load levelling reactors. I can almost guarantee that fusion will never beat solar/wind. Maybe they'd get away with not being NIMBY'd like the fission reactors and overregulated, but if they don't, costs go up.

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