Numerical Analysis Of AC Losses And Quench Behaviors In HTS Composite Tapes

As the superconductors are exposed to an alternating electromagnetic field, AC losses are an key issue to the practical application of superconductors. At the low temperature environment, AC losses is a direct source of heat for a superconducting device, which will not only increase the burden of the refrigeration system and increase the cost of superconductivity application, but also result in the instability of superconducting devices. In a superconducting magnet, the quench triggered by a local temperature rise and the spreading of the normal zone is the threats for its practical application. Due to running with strong current, the quench even results in a destructive damage for superconducting magnet.Based on the finite elment numerical method, the AC losses and quench behavior in high temperature superconducting(HTS) composite tapes are investigated, respectively. Firstly, we analyze the AC losses of single superconducting tape and a stack of tapes. The modeling of superconductor is based on the E-J power law and H-formulation. We compute the AC losses of HTS tapes in different electromagnetic field conditions, such as, thechanges of amplitudes, frequency and phase difference of alternating current and/or magnetic field. Comparing the AC losses of HTS tape and superconductor/ferromagnetic substrate(SC/FM) composite tape, we analyze the effect of magnetic ferromagnetic substrate on the AC losses of HTS tapes in different electromagnetic fields. It is found that the magnetic substrate can increase the AC losses of superconducting tapes at low magnetic field, but at high magnetic field, the magnetic substrate can decrease the AC losses. The AC losses of SC/FM composite tape will decrease with increasing frequency at low magnetic field, however the losses will increase firstly and then decrease with increasing frequency at high magnetic field. The AC losses has a minimum value, as the phase difference is equal to 90 degree; when the magnetic field and current are inphase and antiphase, the AC losses are equal. The effects of magnetic ferromagnetic substrate on multi-layer stacked superconducting tapes are every similar to the effects on single tape.Secondly, the quench process in a stack of composite superconducting tapes is investigaed. The temperature-dependent material parameters of composite superconducting tape is considered in low temperature environment. The thermally coupled H-formulation is used to analyse the magneto-thermal coupled behavior of superconducting tapes. As the superconductor is subjected to a thermal disturbance, the current capacity of superconducting will decrease due to the local temperature rise. The transport current is shared by copper stabilizers in composite superconducting tape, which generates joule heat. Under the adiabatic condition, while the joule heat generated in copper stabilizers is lager than the conductive heat, the temperature will rapidly rise in superconductor. As the temperature in superconducting layer is larger than critical temperature, superconductor turns into nomal state, i.e., superconductor quenches. The joule heat generated in copper stabilizers leads to the quench propagate until the conductor is quenched. By comparing the computational results for the composite superconducting tapes without a defect in superconducting layer and with a defect in superconducting layer. It is found that, the critical current of superconducting conductor with defect decreases, the quench propagation velocity, between the local external heat source and the defect, obviously increases, and the quenching propagates more rapidly in whole superconducting conductor.