Beam Separation at the CERN SPS Collider

The SPS proton-antiproton collider operates with a maximum beam-beam tune shift of about 3 × 10-3 per crossing. The allowable tune spread for acceptable lifetime is limited to less than 0.0251) in order to keep the beams clear of 10th order beam-beam induced resonances. Therefore in order for the machine to operate with more than 3 bunches per beam (6 crossing points), beam separation is required at the unwanted collision points. A prototype scheme2) using 4 electrostatic deflectors was used in the 1984 collider run in order to evaluate the feasibility of running the machine with separated beams. By reversing the polarity of one of the separators it was also possible to produce a small crossing angle (+ 175 µrad) at one of the experimental collision points whilst leaving the orbit around the rest of the machine unperturbed. This experiment is of some interest for the design of the large hadron colliders (SSC and LHC) under consideration at the present time.