IMPROVEMENT OF CAVITY PERFORMANCE BY ELECTRO- POLISHING IN THE 1.3 GHZ NB SUPERCONDUCTING CAVITIES

A steep drop of the cavity quality factor (Qo) at high electric field has been observed frequently in chemically-polished and high-pressure-rinsed Saclay cavities, even in the absence of field emission. Three single-cell cavities from Saclay were tested at KEK following electropolishing and high pressure rinsing. This treatment eliminated the steep Qo drop, the quench field increased to an accelerating gradient of more than 30 MV/m with a quality factor above 2x1010. No dependence of the quench field on the niobium RRR was observed between RRR = 200 and 320 in electropolished cavities.