2018 年 59 巻 8 号 p. 1380-1388
The effects of crack size distribution and voltage probe spacing on the variation of critical current and n-value along the longitudinal direction in heterogeneously cracked superconducting tape were studied using a Monte Carlo simulation combined with a model of crack-induced current shunting. The simulation results were as follows. The variation of the critical current along the longitudinal direction of the tape increases with increasing crack size distribution width, whereas it decreases when the voltage probe spacing is larger. The variation of n-value along the longitudinal direction is larger than that of critical current. The largest crack contributes most to the synthesis of the voltage-current curve, and this contribution increases with the crack size distribution width. Next, a model to predict the upper and lower bounds of distributed critical current and n-values was applied to the simulation results. It was confirmed that the critical current and n-values are within the upper and lower bounds in any crack size distribution width. In addition, it was revealed that the critical current value shifts from the lower to upper bound and the n-value shifts from the upper to lower bound with the increase in the crack size distribution width. Furthermore, an equivalent crack-current shunting model was applied to the simulation results. The multiple n-values for a critical current value and the correlation diagram between the n-value and critical current could be described with this model.
