Parasitic beam crossings

The minimum bunch-to-bunch spacing is a critical parameter in determining the attainable luminosity. As this spacing decreases, the first parasitic crossing moves closer to the interaction point. The effects of one beam on the other at the parasitic crossings must be minimized. It is known that separation distance, bunch current, function, and beam size all influence the beam-beam interaction at the parasitic crossing points. In this design study, the long range beam-beam tune shift (calculated for the first parasitic crossing with bunches spaced by 14 ns) was used as the criterion for choice of optics. With 14 ns spacing, the first parasitic crossing point occurs 2.1 m from the interaction point.