VACUUM PRESSURE RISE WITH INTENSE ION BEAMS IN RHIC∗

When RHIC is filled with bunches of intense ion beams a pressure rise is observed. The pressure rise exceeds the ac-ceptable limit for operation with the design intensities. Ob-servations of events leading to a pressure rise are summa-rized. Relevant parameters include ion species, charge per bunch, bunch spacing, and the location in the ring. Effects that contribute to a pressure rise are discussed, including beam gas ionization and ion desorption, loss-induced gas desorption, and electron desorption from electron clouds.