Hc2(4.2 K) of High-Temperature Superconducting Alloys

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Abstract
Previous measurements of Hc2 versus T in selected Nb3Al1−xGex and Nb3Al alloys for dc magnetic fields to 200 kG and for 14 K ≤ T ≤ Tc have now been extended to 4.2 K by means of pulsed magnetic fields and rf measurements. Long pulse (10 msec) multipalyer coils producing fields to 450 kG were employed for the measurements. At 4.2 K, Hc2≃410 kG and Hc2≃320 kG for the highest Tc, Nb3Al1−xGex and Nb3Al alloys, respectively. These values of Hc2 are the highest measured for any superconductor. Measurements of Hc2 in several related alloys with somewhat lower values of Tc and Hc2 will also be presented. The large values of Hc2 (4.2 K) for all of these alloys permit great latitude of engineering design for practical wire materials. A summary of the physical properties of these high‐temperature superconductors, measurement techniques, present limits of high Hc2 materials, and a current appraisal of technical possibilities will be presented. A summary of some of the measurements has appeared.1