Universal scaling law for quench development in HTSC devices

Full size HTSC magnets and other HTSC devices are becoming a reality. Current density in the HTSC tapes and wires is increasing, especially in the temperature range similar to 20 K. On the other hand, smooth voltage-current characteristics, relatively high operating temperature and low resistive Ag-matrix used in HT superconductors make it difficult to distinguish clearly its normal and superconducting parts. This demands the new approaches for HTSC devices' design to be developed. In many cases, quench in different superconducting devices develops as quasi-stationary overheating if the Joule heat exceeds the heat removal to ambient. For the relatively uniform samples, the quenching current and the quenching temperature at which quench occurs may be derived just from heat balance equations without any use of idea of superconductivity and normal zone propagation. We developed such an approach and showed that near the quench current the time dependencies of the temperature and the electric field obey the universal scaling laws different for the cases less and more than the quench current. The scaling parameters are quench temperature and current, parameters of voltage-current characteristics and cooling. The simple scaling law may be used as a first-step approach to HTSC devices' design. In this paper, scaling theory and its comparison with experiments are presented. The methods to evaluate quench parameters of HTSC devices important for quench protection are suggested. (C) 2000 Elsevier Science Ltd. All rights reserved.