Research On Hybrid Superconductor Based On Combination Of LTS With HTS Coated Conductor

Hybrid superconductor was mainly suggested based on the difference of n value between low temperature superconductor (LTS) and high temperature superconductor (HTS), in which HTS coated conductor has both functions of a stabilizer in part place of metal substrate and current by-pass in LTS conductor. When applied in the production of superconducting magnet, LTS/HTS hybrid superconductor can not only effectively increase the superconducting fill factor and engineering current density, but also improve the cryogenic stability of superconducting magnet against thermal disturbance.In this thesis, the production process of LTS/HTS hybrid superconductor is studied firstly. A HTS cladding layer is produced and its critical current experiment under liquid nitrogen temperature and self-field is performed. Experimental results show that the critical current of the HTS cladding layer does not degrade comparing with its original state, which indicates that it can be combined with LTS conductor to form hybrid superconductor.Since the YBCO CC consists of oxide ceramic and Ni-W alloy which is used as matrix, its flexible properties are not strong enough. Additionally, side-bending characteristic is also important for the application of the hybrid superconductor. Side-bending experiment shows that the critical current of YBCO HTS tapes decreases、with the decrease of side-bending radius. Therefore when the hybrid superconductor is used to wound superconducting magnet, side-bending radius should be larger than its critical radius to ensure its good enough current carrying capacity.According to the structure of the hybrid superconductor and both power-law n value models of NbTi and YBCO CC, current distribution in the hybrid superconductor is numerically analyzed. Due to the different n value in LTS and HTS, the transport current flows initially through the LTS in the hybrid superconductor. If there is a normal-transition in the LTS due to some disturbances, the transport current will immediately transfer to the HTS, then the heat generation can be greatly suppressed and full quench may be avoided. When the temperature exceeds the critical temperature of HTS, the current completely transfers to the metal substrate.Finally, the stability of hybrid superconductor is theoretically analyzed and experimentally tested, respectively. Results show that the minimum quench energy (MQE) of the hybrid superconductor is bigger and the quench propagation velocity (QPV) is smaller than that of the LTS conductor. With the same disturbance, the ability against disturbance and quench recovery of the hybrid superconductor is superior to that of LTS conductor, which indicates that the stability of the hybrid superconductor is significantly improved.