Current sharing and the stability of compositeMgB2 superconductors

Abstract

I–V characteristicsof various MgB2 superconductors were analysed. The transition between the superconducting and normal states ofan MgB2 composite conductor is accompanied by a rapid current redistribution betweenMgB2 filaments and the metallic sheath. It was clarified why the nature of the transition isdifferent at low and at high critical currents. The heat flux and current density inMgB2 and those in the metal sheath at the transition were determined. The transitionof the filaments into a normal state is caused mainly by the heat generated inMgB2 at high critical currents. On the other side, at low critical currents, mainly the heatgenerated in the sheath material is responsible for the transition of a filament.Based on the current redistribution in the matrix, the consequent heat generationand the critical current versus magnetic field dependence, various compositeMgB2 conductors were compared and discussed for their stability.