Critical current density of coated conductors determined from rescaled magnetic moment at temperatures close to 77 K

The possibility of rescaling (or calibrating) of the magnetization results to predict the transport critical current density (Jc) of commercial coated conductors (REBCO tapes) is discussed from both the experimental and theoretical point of view. For this purpose the critical current density in tapes from three different producers was investigated by means of transport and magnetization measurements, in perpendicular magnetic fields of 0.25 T - 2 T at temperatures 65 K - 77 K. Two kinds of samples were tested in the magnetization measurements - square samples 2 × 2 mm2 cut from the central parts of the tapes and elongated rectangular samples of the full tape width (4 mm nominally) and 8 mm length. The transport measurements were performed on full-width samples in a subcooled liquid nitrogen bath. The presented results show that it is possible to empirically rescale the measured magnetization data on the basis of a single transport measurement, achieving the overall accuracy of the transport Jc prediction between 4% and 10% for different tested tapes. Simple theoretical justification and analysis of the empirical scaling is presented, based on the critical state model with the power law current-voltage relation considered to account for different level of electric field in the transport and magnetization measurements.