Speaker
Description
Recent developments in the high Q and high gradient frontier of SRF cavities have focused on altering the surface impurity profile through in-situ baking, furnace baking, and doping to introduce and diffuse impurities such as O, N and C. However, the precise role of each impurity in improving performance is not fully understood. We take a materials-focused approach to identifying the efficiency of O and N impurities. Niobium cavity cutouts are baked at temperatures from 120-800$^\circ$C with and without nitrogen injection as well as subjected to varying amounts of EP removal. Time-of-flight secondary ion mass spectrometry is used to quantify the absolute concentration of each impurity, and these material studies are correlated to the BCS surface resistance measured through cavity tests. These results are compared with BCS theory as well as with first principle calculations. We find that the same reduction in BCS resistance can be realized with either O or N. Furthermore, the concentration of N required is ten times less than that of O to achieve the same improvement in performance.
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