Experiment and Simulation for Normal Zone Propagation of Multifilament MgB₂ Superconducting Wire Cooled by Liquid Hydrogen

摘要

Developing applications of liquid-hydrogen (LH2)cooled superconducting devices is a challenging issue. Since the boiling point of LH2 is 20.4 K, MgB2, whose critical temperature is 39 K, can be cooled with a sufficient temperature margin. Furthermore, MgB2 wire is expected to be used for superconducting equipment due to the low production and material cost. Therefore, in order to design MgB2 superconducting equipment, the knowledge of normal zone propagation phenomena is important for the thermal stability and the quench protection. In this study, normal zone propagation and minimum quench energy (MQE) with a multi-filamentary MgB2 superconducting wire produced by Hitachi, Ltd. were observed under immersed in LH2. In the experiment, heat pulse, which initiates a normal zone, was injected to the center area of 200 cm long MgB2 wire. Then, the MQE and the normal zone propagation velocity (NZPV) were measured under specific conditions. NZPV was in the order of several cm/s and MQE was in the order of a few J at 30 K under LH2 cooling. In order to clarify temperature distribution along the wire during the normal zone propagating phenomena, the simulation model of MgB2 wire cooled by LH2 was created and analyzed using a finite element method simulation software.