Superconducting Mo0.75Re0.25cavities at X-band

RF properties of superconducting Mo0.75Re0.25were studied by performing rf measurements on three TE011mode X-band cavities of the alloy. Cavity surfaces were prepared for testing by means of either electrolytic polishing or uhv anneal. From the temperature-dependent unloaded Q(Qo) of the cavities, the surface resistance of the alloy as a function of temperature, R(T), in the temperature range 4.2K to 1.4K was determined. From the R(T) plots, the residual surface resistance, Ro, and the superconducting energy gap parameter, Δ(0), were obtainable. The highest Qomeasured was 1.4 × 10⁹, corresponding to a Roof 5.7 × 10^-7Ω. The average value of the energy gap parameter, Δ(0), was (1.78 ± 0.04)kBTC. Magnetic breakdown fields, Hcrf, were also determined by measuring Qoas a function of peak surface magnetic field. The highest value of Hcrffound for the alloy was 176G. We discuss cavity performance as a function of surface preparation, aging and atmospheric exposure.