Stability experimental results of cable-in-conduit superconductor for fusion

In case of the forced-flow cooling, the design basis should be established regarding the stability, the static pressure drop and the transient pressure rise during quench which are more serious than that of the pool-boiling cooling coils by liquid helium. For this purpose, JAERI constructed a 15-kA cable-in-conduit conductor whose major parameters is based on a real conductor of FER and measured the stability, the pressure drop, and the pressure rise characteristics by using the Superconducting Engineering Test Facility (SETF). The following conclusions are obtained by this experiment in which a disturbance is applied to a part of the conductor by an inductive heater for a heating time duration of 6 msec. Two types of quench, which are quench at the heated zone and at the down stream region, are observed and the down stream quench is serious for the forced-flow cooling coils because the down stream quench is caused by a lesser disturbance than the heated zone. The heated zone conductor is cooled by a transient heat transfer and an induced flow which give a higher cooling capability than the steady flow in the down stream region. The calculated stability characteristics by an analysis code ALPHE-II are in good agreement with the measured value. The down stream quench is caused by hot helium flowing from the heated zone to the down stream and the stability margin measured is in good agreement with the calculated value by a simple energy balance based on the quasi-static process. The friction factor of a cable-in-conduit conductor has a smooth slope and is in good agreement with the equation for turbulent flow. In addition, the friction factor is roughly twice that of a smooth tube. The pressure rise obtained in a full quench condition is in good agreement with the calculated value by the ALPHE-II and linearly increases as the heating energy to the helium is increased.