Asymmetry of normal zone propagation velocity with respect to current in a multifilamentary composite superconductor

We have observed the phenomenon of destruction of superconductivity by current in a high current multifilamentary composite superconductor. This bronze stabilized conductor had rectangular dimensions of 0.56 cm × 0.17 cm, contained 67,507 Nb3Sn filaments of about 5.8-μm diam and had a self-field critical current at 0 K of about 6.1 kA. The velocity of normal zone propagation was measured on a 56-cm-long sample of this conductor in a vacuum environment. Currents ranged from 200 A to 900 A and initial sample temperatures ranged from 14.5 K to 16 K. We observed a significant dependence of the velocity on the direction of the current. Because there is essentially zero heat transfer into a surrounding environment, the effect must relate to an asymmetry of the fundamental interactions between current and heat flow in the filaments.