Recovering the performance of irradiated high-temperature superconductors for use in fusion magnets
Raphael Unterrainer, David X Fischer, Alena Lorenz, M. Eisterer
Abstract
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, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>T</mml:mi> <mml:mrow> <mml:mtext>c</mml:mtext> </mml:mrow> </mml:msub> </mml:math> , and the critical current density, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>j</mml:mi> <mml:mrow> <mml:mtext>c</mml:mtext> </mml:mrow> </mml:msub> </mml:math> , and discuss possibilities to counteract the degradation using thermal treatments. We found that the degradation in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>T</mml:mi> <mml:mrow> <mml:mtext>c</mml:mtext> </mml:mrow> </mml:msub> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>j</mml:mi> <mml:mrow> <mml:mtext>c</mml:mtext> </mml:mrow> </mml:msub> </mml:math> are closely related to each other, likely due to the expected loss of superfluid density; thus, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>T</mml:mi> <mml:mrow> <mml:mtext>c</mml:mtext> </mml:mrow> </mml:msub> </mml:math> 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 ∘ C and about 60% at 400 ∘ C, which would more than double the magnet’s lifetime. However, a loss of oxygen has to be impeded in the latter case.