Review of stability in high temperature superconductors with emphasis on flux jumping

Abstract

Stability predictions regarding cryostability, minimum propagating zones and quench protection are reviewed with respect to the possible use of high T c superconductors (SC) in current carrying devices. The stability behaviour at liquid nitrogen temperature should be comparable (or slightly superior) to that of conventional SC at liquid helium temperature, and the performance at liquid neon temperature (≈ 27 K) should be much better. No experimental results are available. With regard to flux jumping, rather high flux jump fields which increase approximately linearly with temperature to maxima of ≈ 10 T (compared to 0.4 T for conventional SC) at T/ T c ≈ 0.8 are calculated. Magnetization experiments confirm the theoretical expectations up to T ≈ 15 K. The experimental limit so far is set by the penetration field (given by specimen dimension × critical current density), which must be higher than the flux jump field. Flux jumps are also seen in experiments with shielding, magnetization of rings and torque magnetometers. Qualitatively these manifestations agree to a fair level with corresponding observations in conventional SC.