Research On Electromagnetic Characteristics And Stability Of LTS/HTS Hybrid Superconductors

Electromagnetic characteristics and stability of LTS/HTS hybrid superconductor are researched in this. The theoretical model of LTS/HTS hybrid superconductors is established. Then current distribution, current transfer characteristics, AC losses and stability of LTS/HTS hybrid superconductors are both theoretically and experimentally studied.Research results of current distribution show the following. Below the critical temperature(Tc) of LTS, the operating current is mainly in LTS. Above Tc of LTS, LTS quenching, the current transfers from LTS to HTS, and the operating current is mainly in HTS. When the temperature is higher than Tc of HTS, HTS quenching too, the current transfers from HTS to the metal matrix, so the operating current is mainly borne by the metal matrix. The stronger external magnet field, the greater current in HTS.Research results of current transfer characteristics show that at the case of small operating current, the current sharing temperature of LTS/HTS hybrid superconductors is close to that of LTS and at the case of large operating current, the current sharing temperature of LTS/HTS hybrid superconductors is close to that of HTS. The greater the current ratio in HTS is, the higher the current sharing temperature is. The current sharing length of NbTi/Bi2223 hybrid superconductors measured experimentally is in accordance with the result of numerical simulation.Based on Bean critical model, numerical simulation on AC loss characteristics of a thin superconducting tube is presented. The results are in good agreement with experiments. This numerical simulation method is perhaps applicable for coated superconductors. According to AC loss characteristics of superconducting strip, superconducting cylinder and superconducting tube, AC loss characteristics of LTS/HTS hybrid superconductors are discussed. The results of simulation and experiments show the following. Below Tc of LTS, AC losses are generated almost entirely by LTS. When the temperature is between critical temperatures of LTS and HTS, AC losses are mainly generated by HTS. Simultaneously, experimental results indicate AC losses are linear with the frequency of the operating current.Based on n power-law model, the quench propagation velocity(QPV) and the minimum quench energy(MQE) are numerically analyzed by finite element method(FEM). Simulation results show that MQE of the hybrid conductor is much higher than that of LTS but smaller than that of HTS. QPV is between LTS and HTS. The stability of LTS/HTS hybrid superconductors is also experimentally studied. The experimental results indicate:MQE of the hybrid conductor is greater than that of LTS, QPV and QRT are both less than those of LTS. So the stability of the hybrid superconductor is better than LTS.With advantages of greater engineering current density and better stability, the hybrid superconductor is expected to have potential application in large scale magnet and conducting-cooled magnet particularly.