Experimental study of the current redistribution in pulsed operation inside the Nb/sub 3/Sn CICC of an ITER relevant magnet

It is believed that critical current reduction in multistrand superconducting cables at nonsteady state conditions is caused by a nonuniform current distribution among strands. This was experimentally proven for small model cables, but is still not verified for large cables. In the ENEA Frascati Laboratory, an ITER relevant, large superconducting magnet has been tested at different field ramp rates. By means of numerous local miniature field sensors (Hall probes and pickup coils) located in a few positions along the conductor, current redistribution phenomena inside the cable have been studied. Fast and slow local field changes have been studied to quantify the current nonuniformity. It has been shown that severe current nonuniformity does exist in the cable and that induced current loops are generated, which decay with very long time constants (up to 10/sup 4/-10/sup 5/ s).