CRITICAL-CURRENT RECOVERY IN AG-SHEATHED BI(2223) TAPES AFTER BENDINGAND STRAIGHTENING

We observed an interesting time-dependent recovery of critical current in an unsymmetrical Ag-sheathed Bi(2223) multicore tape. The cores we re arranged unsymmetrically relative to the neutral axis of the tape. The phenomenon was observable after the tape had been bent on the side containing more Bi(2223) cores to a certain diameter in a distinct in terval and then straightened at room temperature and immersed in liqui d nitrogen. We explain the observed behaviour as follows: (i) on bendi ng, the Bi(2223) grains are wedged together and then, on straightening , they are drawn away and (ii) after immersion in liquid nitrogen the grains slowly glide together again under the compressive action of the Ag sheath.