Experimental study of the current redistribution in pulsed operation inside the Nb3SnCICC of an ITER relevant magnet

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