Conductor design for superfluid Helium II

This paper derives some design formulas and charts for a high-field (12 Tesla) application using Nb43Ti25Ta alloy superconductor. This material is selected because of its large critical current (Jc= 71,000 A/cm²) at 12 Tesla and 1.8K. Its ductility is beneficial to manufacturing processes and accommodating of the operating condition under stress. A coil packing factor of 70% and an insulation void fraction of 35% are assumed. These are nominal values which, after analysis, leave adequate turn-to-turn space for insulation bearing area, Helium II volume, and voltage standoff. The stabilizer is oxygen-free, high-purity copper in the full-hard condition, ρ = 7.17 × 10^-8ohm.cm, wherein the magnetoresistivity at 12 Tesla accounts for 69% of the total. Basing a trial conductor on these assumptions will produce a design very close to optimum. Further refinement would be an iterative process whereby one checks the design against all constraints using the fundamental engineering formulas and makes parametric adjustments as necessary.