Transient stability of large aluminum stabilized superconductors

Very large current composite superconductors have been considered and adopt ed to use in SMES coils and fusion applications, such as the Large Helical Device (LHD), These superconductors have large cross-sectional area of high purity aluminum stabilizer to improve their stability and to enhance the o verall current density. Once a normal-zone is initiated in such a composite superconductor, the current transfers to the aluminum stabilizer according to the temperature distribution. The time constant of current diffusion in the stabilizer, however, is very long due to the low electrical resistivit y of aluminum and the large conductor size. Therefore, an excess joule heat is generated in a small area near superconducting filaments and the temper ature increases locally. In this paper, to evaluate this peculiar property we carry out some simulations with regard to quench process in the supercon ductor applied to the helical coil of LHD in National Institute for Fusion Science, The simulations by using a newly developed computer code are compa red with the experimental results of the stability tests on the short sampl es of LHD conductor. Furthermore, we focus on the influence of the CuNi all oy clad adopted to the LHD conductor on the normal transition and normal-zo ne propagation properties.