Self-consistent Orbits for Beam-beam Interactions in the LHC

In part of the straight sections of the LHC the two beams share acommon beam tube. Therefore the bunches cross each other not only at theinteraction point, but as well at many places on either side, with a typical transverse separation of 10 times the transverse beam size. These"parasitic" encounters lead to orbit distortions and tune shifts, in addition to higher order effects. Since the string of bunches from the injection machine contains gaps, not all possible 3564 "buckets"around the machine are filled, but only about 3000. This in turncauses some bunches to not always encounter bunches in the opposite beam at one or several parasitic collision points (so-called "pacman" bunches), or even at the head-on interaction points ("super-pacman" bunches). With a special program self-consistent orbits in the LHC have been calculated for thefirst time with the full beam-beam collision scheme resulting from two bunch filling scenarios. The offsets at the interaction points, and the tune shifts are shown to be small enough to be easily controlled.