Transient stability of a NbTi cable-in-conduit superconductor: Experimental results

The transient stability of a NbTi, cable-in-conduit conductor cooled with supercritical helium was investigated experimentally by inductively heating the conductor for short-time durations. Data were gathered for zero and nonzero imposed flow rates. In addition, some of the zero-flow measurements were taken while the conduit was surrounded by an external vacuum as opposed to the situation where the exterior wall of the conduit was in contact with atmospheric pressure liquid helium. Analysis was carried out by deriving a heat transfer coefficient having both transient and quasi-steady-state components. Results indicate that the theoretical heat transfer coefficients used in most computational studies are inadequate and emphasis should be placed on the rate of cooling between the conductor and the helium rather than on the helium heat capacity; an imposed flow rate of limited magnitude has the greatest effect in the region of multiple stability; an increase in the conductor surface area brings about an increase in both the stability margin and the limiting current; the presence of liquid helium external to the conduit has little or no effect on transient stability.