Recent Results From Nb₃Sn Single Cell Cavities Coated at Jefferson Lab

Because of superior superconducting properties (Tc ~ 18.3K, Hs h ~ 425 mT and ∆ ~ 3.1 meV) compared to niobium, Nb3Sn promise better RF performance (Q0 and Eacc) and/or higher operating temperature (2 K Vs 4.2 K) for SRF cavities. Nb3Sn-coated SRF cavities are produced routinely by depositing a few micron-thick Nb3Sn films on the interior surface of Nb cavities via tin vapor diffusion technique. Early results from Nb3Sn cavities coated with this technique exhibited precipitous low field Q-slope, also known as Wuppertal slope. Several Nb3Sn single cell cavities coated at JLab appeared to exhibit similar Q-slope. RF testing of cavities and materials study of witness samples were continuously used to modify the coating protocol. At best condition, we were able to produce Nb3Sn cavity with Q0 in excess of ≥ 5×1010 at 2 K and ≥ 2×1010 at 4 K up the accelerating gradient of ~15 MV/m, without any significant Q-slope. In this presentation, we will discuss recent results from several Nb3Sn coated single-cell cavities linked with material studies of witness samples, coating process modifications and the possible causative factors to Wuppertal slope.