Development of High-J_c NbTi Multifilamentary Superconducting Wires for AC Use by Introducting Nb Artificial Pins

Abstract

To achieve a further increase in critical current densities of NbTi multifilamentary superconducting wires for AC use, several wires having the theoretically designed Nb island-type artificial pins introduced into NbTi superconducting filaments were fabricated. Oversaturation phenomena were observed whereby F_p increased in the wide range of magnetic field and the position of peak F_p shifted systematically from the low magnetic field side to the high-field side as the reduction rate of artificial pins increased. High critical current densities, such as 1.42×10¹⁰A/m² at 1T (obtained by wire with a filament diameter of the 0.1μm class) 8.7×10⁹A/m² at 2T and 6.1×10⁹A/m² at 3T (obtained by wire with a filament diameter of 0.4μm class) were achieved. Moreover, it was clarified that the field-position of peak F_p was decided by pin interval, d_s, if the correlation length I₆₆ was smaller than half of the fluxoid spacing, a_f. As a result, helpful guideline in designing critical current densities by introducing artificial pins was derived.