Recovering the performance of irradiated high-temperature superconductors for use in fusion magnets

Abstract

Magnets confining the plasma in future fusion devices will be exposed to a significant destructive flux of fast neutrons. In particular, in cost-efficient compact reactor designs, the degradation of the superconductor becomes an issue and directly impacts the commercial viability. We report on the influence of neutron radiation on the superconducting transition temperature, Tc, and the critical current density, jc, and discuss possibilities to counteract the degradation using thermal treatments. We found that the degradation in Tc and jc are closely related to each other, likely due to the expected loss of superfluid density; thus, Tc is a very useful indicator for the magnets' degradation. It increases linearly with the annealing temperature, and around 25% of the decrease can be recovered by annealing at 150 a C and about 60% at 400 a C, which would more than double the magnet's lifetime. However, a loss of oxygen has to be impeded in the latter case.