Quench propagation in a cable-in-conduit force-cooled superconductor-preliminary results

A preliminary test was performed to measure quench propagation in a cable-in-conduit superconductor. Although the data are not extensive, the behavior of the sample was similar to that reported by T. Ando et al. (1989) for tests performed at the same current densities (though at 7-T field). The propagation increased with time, a phenomenon that can only be explained by thermal hydraulics of the coolant. The maximum propagation velocity was about 5 m/s at a current density of 100 A/mm/sup 2/. The propagation velocity (tens of meters per second) predicted by others was not observed. Based on the measured initial normal zone hot helium expansion velocity, the condition for use of the finish time formula of L. Dresner was not met in either the present experiment or in Ando's experiment. It is not clear whether the observed slightly higher power dependence of normal zone velocity on elapsed time is due to changes in helium expansion velocity or is a result of THQ (thermal hydraulic quenchback). Further studies, both analytical and experimental, are needed before the existence of THQ can be verified.