A PROBE FOR THE MEASUREMENT OF THE TRANSPORT CRITICAL-CURRENT DENSITY OF SUPERCONDUCTORS IN HIGH MAGNETIC-FIELDS AND AT TEMPERATURES BETWEEN 2-K AND 150-K

A new probe has been designed for the measurement of the critical current density (J(c)(B, T)) of both high- and low-temperature superconductors as a function of field and temperature. With this probe, voltage-current characteristics can be measured in small bore high-field magnets in the temperature range from 2-150 K with noise levels of typically 350 nV RMS. Excellent temperature accuracy and control in high magnetic fields is achieved such that at 4.2 K, for currents up to 300 A, the critical currents measured are accurate to the equivalent of +/-50 mK; at 20 K, up to 30 A, the accuracy is +/-70 mK and at 80 K up to at least 50 A the accuracy is +/-100 mK. The material under study can be short sections of superconducting cables, wires, tapes or thin films. The important design features of the probe are described. The probe's capabilities are demonstrated by presenting J(c)(B, T) data obtained from a commercial multi-filamentary Nb46.5% wtTi wire and a high-temperature Bi2Sr2Ca2Cu3Ox silver-clad tape in magnetic fields up to 15 T.