Stability of a cable in conduit conductor under fast magnetic field variations

Abstract

Under fast magnetic field variations, ac losses are deposited in a Cable in Conduit Conductor (CICC). The corresponding power losses are transferred to helium thanks to the high wetted perimeter of the conductor. The critical energy of the CICC can be expected to be proportional to the high volumetric heat capacity of helium and to the temperature margin. To confirm the expectations, stability tests under a transversal pulsed magnetic field were performed in the Sultan test facility on a prototype JT-60SA conductor sample. The shape of the magnetic field variation as a function of time is a truncated sinusoid. The experimental results are not totally in agreement with expected behavior on two particular points: - the deposited energy in the conductor as a function of the pulsed field amplitude, measured by calorimetry, deviates from the expected quadratic behavior for coupling losses. The deviation is also increasingly dependent on the transport current. - at a given Sultan background magnetic field, the critical energies at low temperature margins are reduced in comparison with expected values. An explanation based on the saturation of parts of the cable is proposed.