Stability Characteristics of the Aluminum Stabilized Superconductor for the LHD Helical Coils

Stability tests have been carried out on the aluminum stabilized composite-type superconductors developed and used for the pool-cooled helical coils of the Large Helical Device (LHD). The longitudinal voltage of a normal zone shows a short-time rise before reaching a final value, which seems to be explained by the rather slow diffusion process of transport current into the pure aluminum stabilizer and the copper housing. The propagation velocity has a finite value even below the recovery current, and it differs depending on the direction of transport current. A numerical analysis dealing with transient thermal and electromagnetic relaxation processes in the aluminum stabilizer well explains the experimentally observed results.