Flux jumps in high-Jc MgB2 bulks during pulsed field magnetization

Abstract

Pulsed field magnetization (PFM) of a high-Jc MgB2 bulk disk has been investigated at 20 K, in which flux jumps frequently occur for high pulsed fields. Using a numerical simulation of the PFM procedure, we estimated the time dependence of the local magnetic field and temperature during PFM. We analyzed the electromagnetic and thermal instability of the high-Jc MgB2 bulk to avoid flux jumps using the time dependence of the critical thickness, dc(t), which shows the upper safety thickness to stabilize the superconductor magnetically, and the minimum propagation zone length, lm(t), to obtain dynamical stability. The values of dc(t) and lm(t) change along the thermally-stabilized direction with increasing temperature below the critical temperature, Tc. However, the flux jump can be qualitatively understood by the local temperature, T(t), which exceeds Tc in the bulk. Finally, possible solutions to avoid flux jumps in high-Jc MgB2 bulks are discussed.