Calculation of pressure profiles in the CESR hardbend and IR regions

Abstract

In the ultrahigh vacuum system of a storage ring, it is very difficult to measure directly the pressure profiles, due to the limited number of vacuum gauges and the gas-conductance limited nature of the storage ring UHV system. A linear finite-element method was developed and employed to calculate the pressure profiles in the DIP-pumped hardbend region and the TiSP-pumped interaction region of CESR. The calculated pressure profiles were compared under controlled experimental conditions against the pressure measured by the gauges. In the experiment, a calibrated leak was used to introduce CO gas at a known flow-rate into the CESR vacuum chambers near the IR and a series of pressure distributions were measured with various ion pump on/off combinations. Very good agreement was observed between the measurements and the calculated profiles. The pressure profile in these regions is crucial in understanding the residual-gas related backgrounds in the detector. Furthermore, using synchrotron radiation profiles for beam-induced outgassing rates, the pressure profiles in the upgraded Phase 3 CESR interaction region are calculated in order to evaluate the UHV system design.