Submitted by jarome on Thu, 04/17/2014 - 08:09

In reply to by John Sheffield

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Glen has done a detailed study of the issue of handling disruption power on the wall in ITER, and basically just a few disruptions will put a hole in the vacuum vessel. ITER also will have a huge amount (~10 MA) of runaway electrons (produced by the loop voltage) that will have to be handled in a disruption. There are no wall materials that are good enough to handle a disruption, which probably will not deposit its energy uniformly.

John is right about the issue of particle/power-handling in a running steady-state tokamak or stellarator. It is certainly an area of needed research for both confinement types. But you could design a stellarator to have more than one divertor region per period to increase the area. I disagree about the "weird orbits." The whole idea of the quasi configurations is that you get a third quasi-constant of the motion, which confines the energetic ions better than in a conventional stellarator. That being said, the orbits (which conserve J*) certainly have a larger radial extent than banana orbits in a tokamak.

ITER does not have a self-consistent design, let alone a self-consistent burning operational scenario. It is unclear whether either a tokamak or a stellarator could be an economic power reactor. If the wall problem cannot be solved, perhaps a liquid metal wall will be required (immune to neutron damage). In this case, toroidal configurations cannot be used at all. These are all good reasons to stop ITER and to continue research on materials and alternatives to tokamaks.

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