Ramp-rate limitation experiments in support of the TPX magnets

Fast magnetic field change is required for full-size tokamak reactors. The poloidal field magnets are usually ramped to full field at 1.2 T/s, and see pulsed fields of up to 20 T/s during plasma initiation. A new facility has been constructed at M.I.T. that simulates the expected operating conditions of the Tokamak Physics Experiment (TPX) magnets. New features in this facility include (1) a superconducting pulse coil that can superimpose high ramp-down rates, up to 25 T/s, (2 T in 80 msec) on a background field up to 5 T, (2) new power supplies that can supply high rates of dI/dt and dB/dt to the sample under test and the pulse coil, and (3) a forced-flow supercritical helium system that can simulate cooling conditions within the winding pack. The first sample tested in the facility is a 27-strand sub-cable, using 3.1:1 copper/non-copper ratio Nb₃Sn superconductor, typical of the strands to be used in ten of the poloidal field system magnets. This paper presents the first experimental results on the ramp rate limitation of the sub-size cable sample of TPX PF coil conductor. The transient stability at high ramp rate fields will be discussed