Elimination of Current Dissipation in High Transition Temperature Superconductors

Abstract

The relaxation of the shielding current-induced magnetic moment in YBa₂Cu₃O₇ thin films, which were grown in situ, is studied as a function of temperature. Although typical relaxations cause a large amount of decay in the magnetic shielding current (on the order of 10 to 20 percent for the first 1000 seconds), it is shown that this is not necessarily a serious problem for applications such as magnets operating in persistent-current modes. This is because the decay of the magnetic shielding current depends sensitively on how far away the operating current density is from the critical current density J_c. By using a quenching process the shielding current is reduced slightly below J_c and the relaxation is dramatically reduced. A general relation between the relaxation rate at J_c and the reduction of the relaxation rate upon lowering of the operating current is obtained and is shown to be consistent with experimental data.