A Variable Composition, High Field Superconducting Solenoid

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Abstract
In previous work we described the fabrication of cold-worked niobium plus 25% zirconium wire and the use of such wire to construct a solenoid in which a field of 58±1 kG was achieved under loss-free superconducting conditions. We have continued these experiments with other compositions and find that the critical current in short samples at 21 000 G and 4.2°K decreases with increasing zirconium content for the compositions investigated, namely, Nb+25% Zr, Nb+33% Zr, and Nb+50% Zr. Kunzler observed that the magnetic field required to destroy the supercurrent in these alloys increased with increasing zirconium concentration in the same range of compositions. This behavior led us to build a new solenoid composed of several concentric sections with the lowest composition (25% Zr) on the outside and the highest composition (50% Zr) on the inside. Experiments with this coil are discussed.