Summary of Pressure Rise Workshop*

This article summarizes the 13th ICFA Beam Dynamics Mini-Workshop Beam-Induced Pressure Rise in Rings (BNL, Dec. 9-12, 2003) [1]. BACKGROUND OF WORKSHOP Beam induced pressure rise was an intensity limit at CERN ISR during the early 1970's. The beam gas ionization created pressure rise caused more gas ionization, resulting in pressure run-away at high beam intensity. Extensive baking, chamber treatment, and perhaps more importantly, a lot of added pumps helped raise the intensity threshold. Due to the large charge exchange cross sections low energy heavy ion machines such as the AGS Booster, CERN LEAR, and GSI SIS require very high vacuum to obtain good beam lifetime. Nevertheless, the beam loss/gas ionization created pressure rise increases with beam intensity, limiting the maximum attainable intensity. Pressure rise can also be created by electron stimulated desorption if an electron cloud has been formed by the beam. For most machines, electron cloud induced beam instability and/or beam emittance growth limit the beam intensity before pressure rise does. A special case is the RHIC, where electron clouds occur only in part of the warm sections (the total warm section is less than 1/4 of the ring). The beam intensity can be increased without inducing beam instability and emittance growth until the pressure rise impacts operation. The beam induced pressure rise is of concern, therefore, for several machines in operation. These include the AGS Booster, the GSI SIS, and the RHIC heavy ion and proton operations. The beam induced pressure rise is also an important issue for machines under construction or being planning. These include the LHC, SNS, LEIR, GSI upgrade, RHICII, eRHIC, and heavy ion fusion accelerators. The Workshop focused on three aspects relevant to the beam induced pressure rise: electron and ion desorption, vacuum chamber coating and treatment, and electron