A Criterion for Determining Stabilizer Thickness of YBCO Coated Conductors Based on Coil Protection

Abstract

The purpose of this study is to propose a criterion for determining stabilizer thickness of YBCO coated conductors. The permissible disturbance energy density in high-temperature superconductors (HTSs) is two or three orders of magnitude greater than that in low-temperature superconductors (LTSs). On the other hand, to enhance the reliability and safety of HTS coils, an establishment of a protection scheme assuming a quench caused by a failure in power supply, cooling system or similar problem is also required for HTS coil systems. Quenching produces excessive temperature or voltage in the coil winding; overheating may cause the conductor to meltdown, or high voltage may punch a hole in the winding. To avoid these types of damages in YBCO coils, a suitable stabilizer thickness must be determined for the sophisticated structure of YBCO coated conductors, which are composed of highly textured thin-film on a flat flexible substrate. Therefore, we investigate the appropriate structure for YBCO coated conductors from the perspective of energy dumping (i.e., quench protection). Based on the protection scheme that the stored magnetic energy in the coils is dumped by an external dump resistance prepared as a quench protection, we derive a function that examines the heat balance of a quenching YBCO coil in an adiabatic condition and propose a criterion using the function to determine an appropriate stabilizer thickness for YBCO coated conductors.