Effect of non-uniform proton irradiation on the critical current of REBCO tapes

Abstract

Generally, uniformly-distributed irradiation defects such as artificial pinning centers improve the critical current, I c, of REBCO tapes in strong external field. On the other hand, at self-field or low field, irradiation is not effective for improving I c. However, if non-uniform pinning center distribution similar to vortex profile is assumed, this would increase I c at selffield. Therefore, in this study, we experimentally investigated the effect of partial irradiation on I c based on the assumption. We prepared REBCO tapes irradiated with trihydrogen cations in the c-axis direction. Three different patterns of defects were examined; overall, edge-only and center-only irradiations. We measured I c at 77 K, 25 K and 15 K using the four terminal method. Results showed that, while I c was not improved after the irradiations for each pattern, I c behaviour depends on the patterns; edge-only-irradiated tapes showed the highest I c and overall irradiation caused the largest I c degradation at 77 K. However, center-only-irradiated tapes showed the lowest critical current at 25 K and 15 K which may be due to enhancement of flux pinning effect at lower temperature. Moreover, pinning centers in the edge region might be more effective to increase I c, though further investigation on the effect of non-uniform pinning centers is required.