A stability criterion for cryocooler-cooled HTS coils

The Magnet technology of a high-temperature superconductor (HTS) with a con duction cooling system by a GM cryocooler has been advanced. It is very imp ortant to understand the thermal and electromagnetic phenomena in HTS tapes for HTS coil design. We have measured the quench characteristics of HTS ta pes with a conduction cooling system of a GM cryocooler and developed a com puter program based on the finite element method (FEM) to investigate the t hermal and electromagnetic behaviors within HTS tapes, From these experimen tal and analytical results, the validity of the computer program has been c onfirmed. In this paper, we discuss a stability criterion for cryocooler-co oled HTS coils by using the computer program. The current at which "thermal runaway" occurs, which depends on the relationship between the cooling pow er of the GM cryocooler and the heat generation within HTS coils, is chosen as a stability criterion. We also investigate the transient thermal and el ectromagnetic behavior in HTS coils.