Mechanisms of Destruction of Superconducting Properties of High-Temperature Superconductors Cooled with Liquid Coolants under Input of AC

Possible macroscopic mechanisms for the destruction of the superconducting properties of a high-temperature YBa 2 Cu 3 O 7 -based superconductor cooled with liquid helium or nitrogen under input of AC are analyzed. It is shown that these mechanisms can be both of thermal and thermoelectrodynamic nature, which is based on the interrelated change in the electromagnetic field induced inside the superconductor and its temperature. Before the emergence of unstable states, intense stable energy dissipation can be observed, which is not taken into account in the current theory of losses. These mechanisms lead to stable supercritical values of the introduced current and the electric field induced inside the superconductor before the onset of instability and, consequently, high permissible overheating. The results discussed expand the scope of practical use of high-temperature superconductors.