MINIMIZING THE PACMAN EFFECT ON THE CLOSED ORBIT

Pacman bunches, in storage rings, experience two deleterious effects: anomalous tune shifts and orbit displacements. The anomalous tune shif ts result in larger effective tune spreads which, as is known, can be compensated by arranging crossing planes 90 degrees relative to each o ther at successive paired interaction points (IPs) separated by half t he ring circumference. This paper evaluates the associated anomalous P acman orbit displacements for such paired interaction points. The anom alous orbit displacements can in turn be minimized by setting the phas e advance between the paired IPs to half the overall phase around the machine. Numerical results are evaluated for the LHC design parameters . The resultant displacements are small and should not significantly a ffect the LHC performance.