Eur. Phys. J. B (2014) 87: 176
https://doi.org/10.1140/epjb/e2014-50157-6

Regular Article

Limiting stable states of high-T_c superconductors in the alternating current modes

¹ Department of Superconducting Magnets, Division of Superconductivity, NBIKS-Center, National Research Center ‘Kurchatov Institute’, Kurchatov’s sq., 1, 123182 Moscow, Russia
² High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan

^a e-mail: vromanovskii@netscape.net

Received: 9 March 2014
Published online: 1 August 2014

Abstract

The limiting current-carrying capacity of high-T_c superconductor and superconducting tape has been studied in the alternating current states. The features that are responsible for their stable formation have been investigated under the conduction-cooled conditions when the operating peak values of the electric field and the current may essentially exceed the corresponding critical values of superconductor. Besides, it has been proved that these peak values are higher than the values of the electric field and the current, which lead to the thermal runaway phenomenon when the current instability onset occurs in the operating modes with direct current. As a result, the stable extremely high heat generation exists in these operating states, which can be called as overloaded states. The limiting stable peak values of charged currents and stability conditions have been determined taking into account the flux creep states of superconductors. The analysis performed has revealed that there exist characteristic times defining the corresponding time windows in the stable development of overloaded states of the alternating current. In order to explain their existence, the basic thermo-electrodynamics mechanisms have been formulated, which have allowed to explain the high stable values of the temperature and the induced electric field before the onset of alternating current instability. In general, it has been shown that the high-T_c superconductors may stably operate in the overloaded alternating current states even under the not intensive cooling conditions at a very high level of heat generation, which is not considered in the existing theory of losses.