The Critical Current of REBCO Coated Conductors and Experimental Observation of Delamination Due to the Screening Current at 4.2 K

In a measurement of the critical current of a rare-earth cuprate (RE-Ba-Cu-O) coated conductor in liquid helium, we found that the coated conductor delaminated under a magnetic field with angles of 10° and 20° relative to the tape surfaces. To explore causes of the delamination, strains in the direction of the tape widths were observed under an increase in the background magnetic field using two kinds of coated conductors: one had a copper stabilizer surrounding the superconducting layer, while the other had a copper stabilizer that was laminated on the tape surface. The former conductor did not delaminate, but the latter conductor delaminated by applying only a background magnetic field in liquid helium. For the above reason, we concluded that some mechanical support was required to prevent the latter coated conductor from delaminating. In fact, the delamination was preventable by a mechanical support born down to the tape surfaces. As a result, we succeeded to measure the critical current of the coated conductor in liquid helium under a background magnetic field. These results suggest that mechanical support for joints in REBCO coils needs careful consideration.