Theoretical Analysis And Experimental Measurement On AC Loss Of HTS Tapes

The AC loss of HTS will increase the burden of the cooling system and affect the stability of the superconducting devices, and the AC susceptibility has important effect on the study of the critical current and magnetic flux pinning. So it is significant to study the AC loss and AC susceptibility of HTS. The two most important electromagnetic characteristics of HTS are studied by theoretical analysis and experimental measurement.Firstly, the calculation model of AC loss of HTS tapes has been established, and the AC losses of two different HTS tapes with different n values and frequencies have been calculated. To solve the problem that the AC losses obtained by different researchers setting different n values and frequencies have no comparability, the scaling law for the transport AC loss of elliptical HTS tapes has been derived. By using this scaling law, the AC loss under any circumstances can be obtained directly. So that the results with different conditions, different calculation methods can be compared with each other, and the correctness of the scaling law has been verified. The AC loss has been calculated by using scaling law in elliptic strip for the first time.Secondly, two calculation models of AC susceptibility of HTS tapes have been established. The AC susceptibility with different frequencies and magnetic field amplitudes are calculated by using the Brandt method, at the same time, the scaling law of AC susceptibility under the applied magnetic field has been derived, and the results have been compared with the results of the Brandt method. The correctness of the AC susceptibility scaling law has been verified in the end. The AC susceptibility considering magnetic field dependence (Jc) with the change of magnetic field has been calculated. This study has important implications for the theoretical calculation of AC susceptibility of HTS tapes.Thirdly, the simulation models of current density and magnetic field of two kinds of HTS tapes have been built by using COMSOL Multiphysics finite element software; and the H formula is combined with the Power Law E-J relation of HTS materials. AC loss has been calculated by the model which is based on the solution of the magnetic field H.Finally, the measurement system for measuring the AC loss of high temperature superconducting tapes have been established. And the AC losses of two generations of HTS tape and BSCCO with different width to thickness ratios have been measured by lock-in amplifier method based on control of the LabVIEW. The measured results have been compared with the computed results and then the correctness of the theoretical model has been verified once again; The integral method of AC loss has been introduced, by using high precision data acquisition card to collect the signal, and using the integral formula to obtain the AC loss.The results obtained by the two methods have been compared, the causes of error have been analyzed.