Flux jump stability in Nb/sub 3/Sn tape

Abstract

GE manufactured Nb/sub 3/Sn tape was examined to determine the influence of critical temperature, both conductor and coil current density (J/sub c/), and tape width on flux jump stability. The onset of flux jump instability was measured in 3 mm wide, copper stabilized tapes reacted to a range of critical currents (I/sub c/) above and below the normal I/sub c/ in production tape. These tapes were stacked in approximations of coil cross sections with and without Insulating interlayer glass cloth. Production tape, 3 mm wide, was found to be stable above 9 Kelvin (K) with normal quantities of interlayer glass when reacted to yield an I/sub c/ no greater than 482 amps at 5 Tesla (T) and 4.2 K. To evaluate low temperature operation in the range of 4-5 K, consistent with cryocooler advances, narrower width tapes were studied as decreasing tape width will decrease the flux jump stability temperature. Flux jump stability was measured in identically reacted tapes slit to 3.0, 2.5, 2.0 and 1.5 mm. The 1.5 mm tape was found to be stable above 6.5 K. Slitting edge damage in the narrow widths was found to be similar for all widths of tape. The I/sub c/ of the narrower tapes were predictably reduced. Decreasing coil current density also decreased the flux jump stability temperature. Nb/sub 3/Sn tape, 3 mm wide, cowound with copper into a solenoid was tested to evaluate lower temperature operation. The coil was stable during both ramping and operation near the short sample I/sub c/ of the tape at 4.2 K.