Study of the Voltage Behavior of Jointless Superconducting 2G Loops During Pulse Magnetization

Low critical temperature superconducting coils can conduct persistent currents with almost no losses, as the technique to make joints is well developed and the resistive losses are negligible. The replacement of these superconductors by high-temperature superconductors may greatly reduce refrigeration costs. However, even though the technique for making these joints has greatly developed over the last years, there are still inherent difficulties associated to that process. Coils made with partially slit 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 magnetization techniques, for instance, by the means of a transformer. The occurrence of persistent current is related to the voltage in the sample, making it interesting to study the voltage behavior for different regions of operation. In this work, a jointless 2G loop was magnetized with pulse magnetization from which the curves of voltage and current as functions of time were obtained. After several tests, it was possible to divide the superconductor behavior into three different stages of operation, depending on the current levels reached: for low current values, the material behaves as a perfect inductor; for current values near the critical current, it behaves as an RL circuit; and for higher values, resistance dependent on the temperature has to be taken into account. A direct relation between persistent current and the arise of a dissipative state was noted and the highest values of persistent current were observed when the pulse was intense enough to produce significant temperature variations in the sample.