The intrinsic quality factor of niobium superconducting cavities shows a strong degradation (Q0-slope) at high fields.
By means of a simple baking around 120°C the Q-slope is removed. This improvement seems easier to achieve when the cavity is electro-polished (EP) than when it is etched by using a standard “buffered chemical polishing” (BCP).
Many experiments have been carried out and different theoretical models developed to explain the Q-slope origin. Comparison between experiments and theories leads us to believe that Q-slope and baking phenomenon are still not explained.
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