Comparing powder magnetization and transport critical current of Bi,Pb(2223) tapes

The magnetic field dependence of the critical current in (Bi,Pb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10+x/ tapes is compared with the magnetization response of isolated grains extracted from the tapes. Special attention is paid to the low-field behavior. The goal of the experiment is to test the widely-used hypothesis that current paths in these tapes contain both weak- and strong- linked branches, which in low field act in parallel. The data agree with this hypothesis; at temperatures above 50 K the powder magnetization drops off exponentially from the self-field to the irreversibility field, while the transport and magnetization currents in the intact tapes show an extra low-field component. Below 50 K the powder behavior becomes less straightforward, but the parallel-path picture in the tapes still holds

Normal zone initiation and propagation in Y-Ba-Cu-O coated conductors with Cu stabilizer

In the ongoing effort to investigate the normal zone behavior of coated conductors, the effects of a localized, pulsed heat disturbance on a YBa2Cu3Ox Ni-alloy conductor with Cu stabilizer was investigated. The sample was conduction cooled by a GM cryocooler in a vacuum environment, establishing nearly adiabatic conditions. A NiCr wire heater mounted on the sample was used to provide the heat pulse that initiated the normal zone. Consecutive voltage taps along the length of both sides of the sample monitored the propagation of the normal zone. Several thermocouples were glued on both sides of the sample to measure the temperature profile of the conductor. The minimum quench energies and normal zone propagation velocities were measured at ambient temperatures from 58 K to 79 K and transport current ranging from 30% to 90% of c. The voltage and temperature profiles are presented and discussed

HTS conductor characterization at 27 K

A Ne-liquefaction system and cryostat has been developed and built to characterize the electrical and mechanical properties of HTS conductors at elevated temperatures. The device makes use of a coil type condenser inside the experiment dewar, which is fed by LHe. Ne-gas entering the dewar at room temperature, liquefies on the coil windings and drips to the bottom of the dewar, where the experiment is located. He-gas and Ne-gas are recovered. Approximately 1.5 l of LNe was condensed into the dewar in about 1 h after precooling of the dewar. The device has been used successfully to measure zero-field and in-field transport properties of Bi-2223 and YBCO high-temperature superconductors at 27 K