Temperature dependence of critical current density of Nb 3Al multifilamentary wires fabricated by Nb-tube and its improved processes

Abstract

The superconducting critical current densities of Nb 3Al multifilamentary wires made by Nb-tube and its improved process have been measured as a function of temperature from 4 K to 16 K and of applied magnetic field up to 15 T. The critical current density of these wires decreases almost linearly with increasing temperature except the region near the critical temperature in the magnetic field. The upper critical field estimated on the basis of data on the critical current density for a Nb 3Al wire made by the improved process is higher than that for a Nb-tube processed one in the entire temperature range. The volume pinning force density of these wires obeys the temperature scaling law well. The critical current density vs. temperature curves can be well reproduced using this relation even in the region near the critical temperature in fields. It is indicated that the critical current density vs. temperature characteristics from OK to the critical temperature may be divided into three temperature regions and the features in each region are discussed within the flux pinning model of the temperature scaling law.