Development of internally stabilized RHQT Nb3Al superconductors

Recent progress in the internally stabilized rapid-heating, quenching and transformation (RHQT) processed Nb3Al superconductors is described and their various features are compared to those of the externally stabilized Cu clad conductor. Based on the favourable feature that Ag is almost non-reactive to Nb during joule heating, we have succeeded in thinning a diffusion barrier of Nb to less than 5 µm in the finished cross section by adopting an Ag rod jacketed with Nb as a stabilizer module when stacking the subelements. The Ag/non-Ag ratio could be increased to as much as 0.345 by additionally replacing the Nb-centre rod of a jelly roll (JR) with Ag. The superconducting properties of the critical current density, the residual resistance ratio, the magnetoresistance and the n-index in the voltage–current characteristic were studied for both as-quenched and subsequently deformed conductors, finally transformed at 800 °C for 10 h. A loading test of a small coil wound with a 30 m length of internally stabilized RHQT JR conductor has shown the uniformity of the internally stabilized conductor used.