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Comment by ivanb | Hacker News Reader

Basic thermodynamics. Particle energy grows as T (because energy = 3/2 kT). Thermal radiation energy grows as T^4. At fusion temperature up to 80% of energy is in radiation. Energy density of radiation in this case is close to energy density of metals. It's impossible to contain such radiation.

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The SPARC design uses a combination of extremely high strength magnetic fields to contain charged particles inside the vacuum chamber and a molten-salt blanket (FLiBe) for neutron capture and cooling. They believe this will be a viable containment system.

And what do they do with gamma radiation? As I said at thermonuclear temperatures it contains majority of the energy of the system.

It is absorbed by the FLiBe salt blanket in the ARC design and converted to heat. The hot salt is circulated out and the heat is used for power generation before the salt is recirculated.

Thanks for explaining. Good luck with removing all this gamma radiation from the system before it vaporizes the chamber but not fast enough as to cool the plasma and stop the reaction. I doubt that this sweet spot exists. Thermonuclear bombs exist only because plasma is surrounded by a thick layer of uranium which absorbs and re-emits gamma radiation thus not letting the plasma to cool. And this layer doesn't have to exist for too long. Less than a millisecond is fine to make a big enough bang.

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