Solvents and pumpdown characteristics of SRF Nb cavities

High-performance superconducting radio frequency (SRF) cavities are placed under UHV and low particulate conditions when they go through the surface treatment process, and are kept under these conditions permanently thereafter, both before and during use in the accelerator. The outgassing of the gasket material in the gate valves and the outgassing of the solvents that come in contact with the gasket and the cavity surfaces determine the ultimate pressure that can be obtained in the cavity. A systematic study of gaskets and various solvents was undertaken in order to understand the conditions that lead to a low ultimate pressure in a short period of time. The results with Kalrez, Viton O-rings and solvents like methanol, acetone, isopropyl and freon will be presented. Also, we discuss the effect of a slow or fast initial pumpdown in order to prevent the settlement of particulates due to condensation.<
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