Design of the Cryopumping Vacuum System for ESCAR

ESCAR is an experimental superconducting accelerating and storage ring for protons. Scattering collisions with residual gas degrades the quality of proton beams that are stored for long time periods. The loss of quality will be small if the average gas density in the path of the beam is kept less than about 106 molecules per cm3, depending upon the gas species. This density corresponds to a room temperature pressure for nitrogen-like gases of 3×10-ll Torr. We plan to achieve this vacuum goal in the ESCAR ring by distributed cryopumping at 4.5°K, the operating temperature of the superconducting magnets. In the magnet sections the cold bore of the magnet will provide the condensing surface. In the straight sections, 4.5°K beam tube or distributed cryopumps will be provided consistent with the function of the particular section. The large cryosurface area provides effective pumping capacity for H2 by utilizing sub-monolayer adsorption. The surfaces can be degassed of H2 by a temperature rise to 15°K. The cycle can be accomplished during routine maintenance periods. We expect the interval between the degassing of the magnet quadrants to be of the order of months. Because of the experimental nature of ESCAR, sector valves will be provided to permit the isolation of each straight section from the ring to allow ready accessibility for equipment testing and modification. Each section will have a roughing and conditioning pumping station.