High Critical-Current Measurements in Liquid and Gaseous Helium
We compared variable-temperature critical-current, Ic(T), measurements up to 200 A on samples immersed in liquid helium to those on samples in flowing helium gas. Multifilamentary Nb-Ti and Nb3Sn samples were used in this study. Ic(T) measurements above 5 K are difficult because these measurements need to be done in helium gas and the heat generated during the measurement and conducted down high-current leads can raise the sample temperature significantly. This creates a large uncertainty and perhaps a sample dependent bias in the sample temperature that occurs even if the measurements are made meticulously. Ic(T) measurements at a constant magnetic field are needed to determine the temperature margin of magnet applications and performance data for cryogen-free applications. The comparison of Ic(T) data in liquid helium to data in gaseous helium, over the temperature range of 4 to 5 K, allows for the inference of sample temperature uncertainty and biases. Agreement to within 30 mK was obtained.
KeywordsCritical Current Density Settling Time Pulse Method Liquid Data Current Contact
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