Ultra high vacuum conditions are not necessary in the cavities baking process to improve the Q-slope at high accelerating fields. Easier to perform, baking in the air at atmospheric pressure can be carried out with the same efficiency. Furthermore, the cavity surface treatment by oxygen plasma shows similar results as baking treatment.
These experiments show that the thickness of oxide layers is not involved in the Q-slope phenomenon, but preserve the possible role played by oxygen towards the Q-slope removal.
Analysis of experimental results obtained with buffered chemical polished (BCP) and electropolished (EP) superconducting niobium cavities, show similar behaviours before and after baking. These experiments demonstrate that surface roughness and magnetic field enhancement at grain boundaries cannot explain the origin of Q-slope.
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