Propagation of normal zones of finite size in large, composite superconductors

Very large, composite superconductors were proposed for use in energy storage magnets. A typical conductor, rated at 230 kA, was discussed by J. Waynert, Y. Eyssa, and X. Huang, namely, a 6-cm aluminum cylinder with superconducting filaments on its outer surface. Owing to its large size and nonuniform distribution of filaments, such a conductor can sustain normal zones of finite size that travel at a uniform velocity along the conductor. A simple, analytical model was presented that permits determination of the conditions under which such zones can exist and the size and velocity of such zones. It was shown that the transport current has a threshold value below which finite normal zones cannot exist and that the propagation velocity corresponding to this threshold current, though not zero, is the smallest possible.