Insight to the Duration of 120 degrees C Baking on the Performance of SRF Niobium Cavities

Low-temperature baking at 100( ?)C-140 C-? in ultrahigh vacuum for several hours is the final cavity processing technique to achieve the highest accelerating gradient cavity by eliminating the high field Q-slope, typically on cavities made of high purity fine grain niobium and subjected to electropolishing. The temperature and duration of baking control the onset of the high field Q-slope and overall quality factor over the baseline measurements. The increase in quality factor is generally related to the reduction in the temperature-dependent surface resistance, which refers to BCS surface resistance due to the reduction in the electronic mean free path and elimination of high field Q-slope is still being actively investigated. Here, we present the results of a series of measurements on 1.3 GHz TESLA shape single-cell cavities with successive low-temperature baking at 120 C-? up to 96 h. The rf loss related to the trapping of residual magnetic field refers to flux trapping sensitivity measured with respect to the duration of 120(?)C bake.