High field Q slope and the effect of low-temperature baking at 3 GHz

A strong degradation of the unloaded quality factor with field, called high field Q slope, is commonly observed above B-p congruent to 100 mT in elliptical superconducting niobium cavities at 1.3 and 1.5 GHz. In the present experiments several 3 GHz niobium cavities were measured up to and above B-p congruent to 100 mT. The measurements show that a high field Q slope phenomenon limits the field reach at this frequency, that the high field Q slope onset field depends weakly on the frequency, and that the high field Q slope can be removed by the typical empirical solution of electropolishing followed by heating to 120 degrees C for 48 hrs. In addition, one of the cavities reached a quench field of 174 mTand its field dependence of the quality factor was compared against global heating predicted by a thermal feedback model.