Relation of Size Distribution of Cracks in Superconducting Layer to Critical Current Distribution under Small Voltage Probe Spacing in REBCO-Superconducting Composite Tape

Abstract

The relation of distribution of crack size to that of critical current under small voltage probe spacing in RE(Y, Sm, Dy, Gd, ….)Ba₂Cu₃O_7−δ layer-coated superconducting tape with stress-induced cracks was studied with a Monte-Carlo simulation method in combination with a model of current shunting at cracks. First, it was shown that the experimentally observed feature that the critical current decreases with increase in distribution width of crack size and voltage probe spacing was reproduced by the present simulation. Then it was revealed that (i) the largest crack among all cracks in the region between the voltage probes plays a dominant role in determination of critical current, and, (ii) when the size of the largest crack is fixed, the large difference in crack size among all cracks acts to raise the critical current value and to reduce the n-value, and, in this phenomenon, the reduction of n-value with increasing difference in crack size is more dominant than the increase of critical current. Finally, it was shown that the distribution of critical current can be described using the Gumbel’s extreme value distribution function as a first approximation under small voltage probe spacing where the influence of the difference in crack size on critical current is relatively small.

The distribution of critical current of the superconducting tape with cracks of different sizes in the superconducting layer under small voltage probe spacing was described satisfactorily with the approach proposed in this work.