Alternating Current Instability of Conduction-Cooled High-Tc Superconductors and Superconducting Tapes
V. R. Romanovskii *
NBIKS-Center, National Research Center “Kurchatov Institute”, Moscow 123182, Russia
K. Watanabe
High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
A. M. Arkharov
Moscow State Bauman Technical University, Moscow 107005, Russia
S. Awaji
High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
N. A. Lavrov
Moscow State Bauman Technical University, Moscow 107005, Russia
V. K. Ozhogina
NBIKS-Center, National Research Center “Kurchatov Institute”, Moscow 123182, Russia
*Author to whom correspondence should be addressed.
Abstract
The AC current instability mechanisms are investigated in high-Tc superconductor and superconducting tape at conduction-cooled conditions when the electric field and applied current may essentially exceed the critical values of a superconductor. It is shown that there exist the characteristic times defining the corresponding time windows that are the basis of the existence of the stable AC regimes despite the high values of the induced electric field and the temperature of a superconductor. It is proved that these values are higher than the corresponding values of the electric field and the temperature before the thermal runaway. These states may be defined as stable overloaded regimes. Therefore, high-Tc superconducting magnets are possible to operate stably at AC overloaded regimes and the conduction-cooled conditions, which will be characterized by very high AC losses.
Keywords: High-temperature superconductor, voltage-current characteristic, current instability, overheating, flux creep