Superconducting properties with high-field peak effect in ohmically-heatedjelly-rolled Nb3Al wire

Jelly-rolled Nb3Al wires with a Nb matrix have been ohmically-heated at con trolled maximum temperatures ranging from 1600 to 2000 degrees C in vacuum, in order to investigate the properties of pinning force densities at high magnetic fields. The samples were 1.34 mm diameter and 50 mm long. To obtai n the stoichiometric composition of the A15 phase, each sample was quenched in vacuum after ohmic-heating. Critical currents have been measured up to 23 T by a four probe method. The critical temperature of the sample heated at 1940 degrees C was 18.3 K. In longitudinal cross-sections, the samples h eated at maximum temperatures less than 1940 degrees C have layer structure s consisting of Nb-rich regions and A15 phase regions. In the sample heated up to 1940 degrees C, which is the melting point of Nb3Al, these layers we re not observed. This sample showed a remarkable peak effect in the critica l current at high magnetic fields, over 20 T.