Carregamento indutivo de corrente em laços supercondutores

Abstract

Low critical temperature superconductors can conduct persistent currents almost without losses, because the technique to make the joints is well developed and the resistive losses are negligible. The replacement of these superconductors by hightemperature superconductors can greatly reduce refrigeration costs. However, the resistive losses related to the joints are relevant. Coils made with loops of high temperature superconducting tape have no joints, and therefore can conduct current in persistent mode. Since there are no terminals, its current must be induced through loading techniques. In this thesis, are investigate the mechanisms that cause induction of persistent current in the superconducting loops in the absence of external field and the results showed that there are lower and higher limits for persistent current induction, and that the appearance of hot spots can impair the charging. Transient models are proposed for the electric field in the loop which take into account the variations of current and power dissipated in the tape, which were validated by a nonlinear adjustment tool from Matlab software. The adjustments results showed good agreement with the experimental data, demonstrating the validity of the models. It is proposed a new method for measuring of the critical current in superconducting loops, and a new coil geometry with loops is presented that not only require a less robust induction system, but can also facilitate charging in the presence of magnetic field.