Enhanced Values of Hc2 in Nb-Ti Ternary and Quaternary Alloys
Recently the fusion community has been very interested in the design of toroidal field magnets for tokamak devices with peak conductor fields of up to 12 T. Such fields cannot be met by the use of Nb-Ti alloys at 4.2 K, since the upper critical field (H c2) is about 11 T at this temperature. However, 12-T operation may be feasible at reduced temperatures in Nb-Ti  or by appropriate alloying of the Nb-Ti, since it is known that the H c2 of Nb-Ti is depressed by its strong normal-state paramag-netism . Previous work, both theoretical  and experimental [5–6], has shown that high-atomic-number additions can reduce the paramagnetic limitation by encouraging spin-orbit scattering processes. Additional possibilities for raising H c2 come from the dependence of H c2 on the normal-state resistivity, p n. The present work reports progress on the fabrication and evaluation of some Nb-Ti, Nb-Ti-Hf, Nb-Ti-Ta, and Nb-Ti-Ta-Hf alloys, some of which have values of H c2 superior to those of standard Nb-Ti alloys.
KeywordsCritical Field Quaternary Alloy Toroidal Field Magnet Electronic Specific Heat Coefficient Tokamak Device
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