Single Bunch Stability in Pep-ii Ler

Preliminary estimates[?] indicate that single bunch in the LER of the PEP-II B-factory has to be stable, both longitudinally and transversely, at the maximum design bunch current 1.8 mA (beam current 3A). However, realistic wakes of the machine has been constructed only recently using results of the extensive numerical simulations of the vacuum components of the ring[?]. Additional to that, the code TRISIM[?], a simulation program for single-bunch collective effects written by one of the authors (G. S.), became recently available. This allows us to study beam stability in a more reliable way than it is possible analytically. In the beginning, we discuss shortly how the wake fields responsible for the effects under consideration have been constructed. Then we present results on the PWD and, later, results on the beam stability obtained with the code TRISIM. The input parameters are based on the nominal parameters of the LER: energy 3.105 GeV, revolution period 7.336 μs, rf voltage 5.1 MeV, RF frequency 476 MHz, SR energy loss 0.75 MEV/turn, momentum compaction α = 1.23× 10−3, average beta function βy = 14.5 m, betatron tune νy = 36.642, horizontal emittance x = 65.58 nm, coupling y/ x = 0.03, damping times τE = 30.2 ms, τy = 61.1 ms. The nominal bunch length of 33.1 ps and the rms energy spread of 2.394 MeV were used to generate the initial distribution of a bunch.