Studies on several factors in the critical current measurement of HTS tapes relating to the VAMAS intercomparison

The recent VAMAS intercomparison on critical current, Ic, measurement in Bi-based oxide tapes revealed that Ic of the tapes was quite sensitive to the heat cycle between room temperature and cryogen temperature. Then, the effect of several factors on Ic of high-Tc tapes with respect to the heat cycle has been studied. Ag-sheathed monocore Bi-2212 and Bi-2223 tapes, and 55 multicore Bi-2223 tapes were prepared by PIT method. The Ic measurement was performed at 4.2 K and 77 K following the guide line of VAMAS intercomparison. The degradation in Ic of the tapes seems to be caused by the waving of those fixed between current terminals. Furthermore, the Ic is drastically degraded by the bubbling in tapes, although the frequency of bubbling is small. Smaller Ag ratio of monocore tapes produces more significant drop in Ic by the heat cycle. The 55 multicore Bi-2223 tapes scarcely show the waving, and the Ic of the tapes is much less sensitive to the heat cycle than that of monocore tapes. The dimension of the core seems to be a key parameter against the Ic degradation in the heat cycle.