An Accurate Model of Beam Ion Instability with Nonlinear Space Charge, Realistic Beam Optics and Multiple Gas Species Vacuum

# Email address: wanglf@slac.stanford.edu An Accurate Model of Beam Ion Instability with Nonlinear Space Charge, Realistic Beam Optics and Multiple Gas Species Vacuum L. Wang # , M. Pivi, T. O. Raubenheimer and J. Safranek SLAC National Accelerator Laboratory, Menlo Park, CA, USA Abstract The previous analyses of beam ion instability have been performed for single gas species only. However, there are multiple gas species in the vacuum chambers of an accelerator. The superposition rule doesn’t apply in general and it overestimates the instability. Therefore, it is important to use multiple gas species model. On the other hand, the variation of beam size along the accelerator ring or linac provides Landau damping to the instability. In previous studies, the effect of beam optics has been represented by a frequency spread and a quality factor. In practice, it could be difficult to accurately estimate the frequency spread and quality factor for general beam optics because the variation of the beam size along the ring usually doesn’t have simple distribution. This paper provides a more accurate method to analyze beam ion instability with arbitrary vacuum component and arbitrary beam optics where the variation of the beam size along the accelerator ring or linac can be arbitrary. Meanwhile, the nonlinear space charge effect is also included and the general beam filling pattern can be easily modeled. Our analyses agree well with expensive simulations. PACS numbers: 29.27.Bd, 29.20.db