Beam-Beam Interaction and Pacman Effects in the SSC (Superconducting Super Collider) with Random Nonlinear Multipoles.

摘要

In order to find the combined effects of beam-beam interaction (head-on and long-range) and random nonlinear multipoles in dipole magnets, transverse tunes and smears have been calculated as a function of oscillation amplitudes. Two types of particles, ''regular'' and ''pacman,'' have been investigated using a modified version of the tracking code TEAPOT. Regular particles experience beam-beam interactions in all four interaction regions (IR's), both head-on and long-range, while pacman particles interact with bunches of the other beam in one medium-beta and one low-beta IR's only. The model for the beam-beam interaction is of weak-strong type and the strong beam is assumed to have a round Gaussian charge distribution. Furthermore, it is assumed that the vertical closed orbit deviation arising from the finite crossing angle of 70 mu rad is perfectly compensated for regular particles. The same compensation applied to pacman particles creates a closed orbit distortion. Linear tunes are adjusted for regular particles to the design values but there are no nonlinear corrections except for chromaticity correcting sextupoles in two families. Results obtained in this study do not show any reduction of dynamic or linear apertures for pacman particles when the oscillation amplitude is less than approximately 10 sigma. However, smears often exhibit a strong dependence on tunes, casting some doubts on the validity of defining the linear aperture from the smear alone. 10 refs., 16 figs., 3 tabs.