A probe for investigating the effects of temperature, strain, and magnetic field on transport critical currents in superconducting wires and tapes

Abstract

A probe for investigating the eects of temperature, strain, and magnetic eld on transport critical currents in superconducting wires and tapes.', Review of scientic instruments., 71 (12). pp. 4521-4530.

Reversible and irreversible effects of strain on the critical current density of a niobium–tin superconducting wire

“…Measurements were made on a 0.6 mm diameter jellyroll Nb 3 Sn wire using the Durham J c ðB; T ; eÞ probe [8]. The wire was heat-treated in an argon atmosphere on a stainless steel mandrel and then transferred, copperplated and soldered to a copper-beryllium alloy spring sample-holder using a procedure well documented elsewhere [8,9].…”

“…The wire was heat-treated in an argon atmosphere on a stainless steel mandrel and then transferred, copperplated and soldered to a copper-beryllium alloy spring sample-holder using a procedure well documented elsewhere [8,9]. The strain was applied by twisting one end of the spring with respect to the other, where the magnitude of the strain had been previously calibrated using standard cryogenic strain gauges [8]. The spring material has an elastic limit of $1% at 4.2 K, and a similar thermal contraction to multifilamentary Nb 3 Sn wires [8].…”

Final Technical Report

“…The new apparatus allows us to measure the strand in compression and tension to cover a range of applied strain typically from −1 % to +1 %, based on Cheggour's original design [18,19] ("Durham probe" using a "Walter's spring" technique [20]). The variable temperature design utilizes our high-rate helium gas flow and gas temperature pre-regulation approach that was developed at NIST.…”

“…The magnetic field was swept from 0 to 16 T, and then back to 0 T again. We used fixed temperatures of 4, 4.5, 5,6,7,8,9,10,11,12,14,16,18,20,25,30,35, 40 and 76 K. Measurements at 4, 4.5, and 5 K were done in liquid helium and those at 76 K were done in liquid nitrogen. Our re-entrant Dewar can be filled with a liquid cryogen, pressurized, and heated to change the temperature of the cryogen.…”

Critical current measurement with spatial periodic bending imposed by electromagnetic force on a standard test barrel with slots

“…Influence of the axial strain can be studied with having a force applied on a free suspended sample, 1,4 a sample mounted on a spiraled substrate, 5,6 ͑so-called Walters spring͒, and a method based on a straight beam section that is part of a U-shaped bending spring 7 or alternatively to an initially curved beam 8 ͑so-called pacman͒. For applied transverse strain, we can distinguish between homogeneously distributed loads on a wire, being, for example, sandwiched between flat surfaces, 9,10 spatial periodically applied stress by using crossing strands, 11,12 and finally bending strain.…”