Estimations of Beam Lifetimes in the SIS18

Abstract

The present developments for high current operation with U28+ in the SIS focus on the efficient collimation of projectile stripping losses and on the subsequent pumping of the desorbed molecules. Beside the projectile ionization and beam loss, the desorption induced by residual gas (target) ionization could also play a role in the dynamic vacuum pressure at the typical SIS18 ion beam energies. We describe a simplified model for the dynamic pressure that is based on the estimated and expected desorption yields as well as on the known cross sections for projectile and target ionization. We integrate the model over realistic SIS acceleration ramps and predict the beam life time. From our model we obtain the fractional beam loss under stable (but dynamic) vacuum conditions for different beam ions.