New low-impedance vacuum chambers were installed in the SLC damping rings for the 1994 run after finding a single bunch instability with the old chamber. Although the threshold is lower with the new vacuum chamber, the instability is less severe, and we are now routinely operating at intensities of 4.5× 10 10 particles per bunch (ppb) compared to 3× 10 10 ppb in 1993. The vacuum chamber upgrade is described, and measurements of the bunch length, energy spread, and frequency and time domain signatures of the instability are presented.
Using normalized one-turn resonance-basis Lie genera tors in conjunction with an action-angle tracking algorithm (nPB tracking), we have been able to better understand the relationship between the dynamic aperture and lattice nonlinearities. Tunes, tune shifts with amplitude and/or energy, and resonance strengths may be freely changed to probe their individual impact on the dynamic aperture. Fast beam-beam simulations can be performed with the in clusion of nonlinear lattice effects. Examples from studies of the PEP-II lattices are given.
With a newly developed algorithm using resonance ba sis Lie generators and their evaluation with action-angle Poisson bracket maps (nPB tracking) we have been able Lo perform fasl tracking for dynamic aperture studies of PEP-II lattices as well as incorporate lattice n on linearities in beam-beam studies [l]. We have been able to better un derstand the relationship between dynamic apertures and the tune shift and resonance coefficients in the generators of the one-turn rr»aps [2]. To obtain swamp plots (dynamic aperture vs. working point) of the PEP-II lattices, we firsL compute a one-turn resonance basis map for a nominal working point and then perform nPB tracking by switch ing the working point while holding fixed all other terms in the map. Results have been spot-checked by comparing with element-by-element tracking.
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