CURRENT TRANSFER CONDITIONS FROM A METALLIC CONDUCTOR TO A HIGH-TC SUPERCONDUCTOR

The quality of the electrical contact between a metal and a high T(c) superconductor is of primary importance for practical applications and may influence the result of transport J(c) measurements. In melt-textured growth (MTG) samples the current density in the contacts can be very high and dissipation may cause heating which can lead to faulty measurements or even to thermal runaway. The losses are determined by the resistance of the normal metal, the contact resistance and the transfer length in the Y-Ba-Cu-O. Methods to establish low resistivity contacts with a very low loss level at high current densities are currently being evaluated. Even when such low resistance contacts are realized, the sample often breaks under the Lorentz force or forces due to differential thermal contractions of the sample holder. To avoid this problem, a new sample holder has been developed which reinforces the sample and optimizes the geometry of the normal conducting part to achieve good heat exchange to the cryogenic liquid and to reduce the Joule heating. The influence of the sample holder on thermal stability is discussed and the J(c) values at different temperatures and fields are presented.