Influence of irradiation temperature on REBCO tape degradation

Abstract Commercial rare earth barium copper oxide (REBCO) coated conductor tapes were irradiated at temperatures ranging from 20 to 300 K with 1.2 MeV protons up to fluences of 10 21 m −2 . With in situ transport current measurements, we found that self-field critical currents ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi mathvariant="italic">I</mml:mi> <mml:mtext>c</mml:mtext> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> ) and transition temperature ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi mathvariant="italic">T</mml:mi> <mml:mtext>c</mml:mtext> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> ) degrade in cold (20–200 K) irradiations by a factor of 1.6 faster than in 300 K irradiations. This warrants caution when basing the development of REBCO fusion magnets, which are operated at 20 K, on results from room-temperature irradiations. The degradation of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi mathvariant="italic">I</mml:mi> <mml:mtext>c</mml:mtext> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> , n-value and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi mathvariant="italic">T</mml:mi> <mml:mtext>c</mml:mtext> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> for irradiations in the range 20–200 K closely matched each other. However, small annealing effects can already be observed at 80 K, which is a lower threshold than previously thought. The observed <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi mathvariant="italic">I</mml:mi> <mml:mtext>c</mml:mtext> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> recovery increases with annealing temperature and is at 300 K four times higher than at 200 K. And finally, we compared the experimental data from this study with the calculated decrease of superfluid density, and find a surprisingly good correlation, supporting the Eisterer hypothesis for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi mathvariant="italic">I</mml:mi> <mml:mtext>c</mml:mtext> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> degradation.