TRANSIENT ANALYSIS AND BURNOUT OF HIGH-TEMPERATURE SUPERCONDUCTING CURRENT LEADS

The transient behaviour of high-temperature superconductor (HTS) curre nt leads operated between liquid helium and liquid nitrogen temperatur es is analysed for burnout conditions upon transition of the HTS into the normal state. Leads composed of HTS only and of HTS sheathed by pu re silver or silver alloy are investigated numerically for temperature -dependent properties and analytically for temperature-independent pro perties. For lower values of shape factor (current density times lengt h), the lead can be operated indefinitely without burnout. At higher v alues of shape factor, the lead reaches burnout in a finite time. With high current densities, the leads heat adiabatically. For a fixed sha pe factor, low current densities are desired to achieve long burnout t imes. To achieve a low helium boil-off rate in the superconducting sta te without danger of burnout, there is a preferred temperature depende nce for thermal conductivity, and silver alloy sheaths are preferred t o pure silver sheaths. However, for a given current density, pure silv er sheaths take longer to burn out.