Novel methods for the measurement of the critical current of superconducting wires

Abstract

The critical current as a function of magnetic field of superconducting wires is commonly measured using about 60 mm short straight, or U-shaped samples, or about 1 m long samples on helical mandrels (so-called ITER barrels). The ITER barrel is designed for low to medium currents, but is commonly modified for high current wires. This often results in increased complexity, errors from reacted sample handling, preparation time, and cost. We have developed a method that retains the standard ITER barrel, but uses disposable, off the-shelf, plumbers, Cu tube fittings instead of machined end-rings, thereby resolving the aforementioned issues. The improved sample holder also solves a number of disadvantages of the original ITER barrel method. A second method involves the improvement of straight wire measurements. Current redistributions, resulting from the limited length in perpendicular magnetic field, reduce the achievable voltage resolution in short straight, or U-shaped samples. We have introduced "wiggles" in U-shaped short samples, which impose the appropriate current distribution far before the region of interest, thereby mitigating undesired redistributions around the voltage measurement region. Both improved methods allow for an increased throughput and reliability of critical current measurements on superconducting wires.