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Given the extremely high plasma temperatures that are required to sustain a nuclear fusion reaction in a device such as a tokamak reactor, how can such high temperatures be maintained in the presence of radiative heat transfer from the plasma to the walls of the reactor vessel?

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    $\begingroup$ Well, the walls get hot. Which rather limits the options on materials. ITER’s divertor will be either tungsten or graphite, with lots of cooling behind it. $\endgroup$
    – Jon Custer
    Dec 24, 2020 at 2:25

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This is a really big problem, for at least two reasons.

First, when trying to get the plasma energetic enough to support fusion, the plasma in response tries very strongly to radiate its heat away. That radiated heat has to be continuously replentished in order to hold the desired temperature.

Second, the plasma temperature is sufficient to rip apart anything you might want to build the containment vessel out of, which means the plasma has to be held away from the walls so they do not instantly vaporize. Magnetic fields are used for this purpose.

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  • $\begingroup$ Niels, I am aware that magnetic fields are used to confine the plasma, but those fields can't contain electromagnetic radiation. This fact makes me question whether or not net positive fusion energy production is possible on earth, because the radiative heat transfer out of the plasma must be huge. $\endgroup$ Dec 24, 2020 at 16:45
  • $\begingroup$ it is huge, and you are right that the magnetic field cannot contain the EM radiation, but I do not know enough about fusion physics to answer your question, sorry- NN $\endgroup$ Dec 24, 2020 at 18:31
  • $\begingroup$ It would be "convenient" if the walls of the tokamak were mirrored such that radiation was reflected back into the plasma, but I've never seen pictures that showed that, and I'm sure that the designers already thought of that. $\endgroup$ Dec 24, 2020 at 18:44
  • $\begingroup$ plus, at the energies typical of the fusion core, the departing photons would most likely penetrate the walls instead of bouncing off them. $\endgroup$ Dec 24, 2020 at 23:33

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