Beam-beam effects in the strong-strong regime at the CERN-SPS

The authors report observations on beam-beam effects at injection and during store in the strong-strong regime of the SPS (Super Proton Synchrotron) and compare them with earlier observabilities. It is shown that, for the operation with six bunches per beam and a linear tune shift of about 0.005 per collision, a small fraction of the particles is lost during injection and acceleration due to the beam-beam interaction. In particular, losses are caused by the seventh-order resonance. Resonances of odd orders are created by the insufficient separation of the beams at some of the crossing points. An upgrade of the separation scheme will reduce the losses. During store the beam-beam force creates resonances of high order. If the emittances of both beams are similar, resonances up to tenth order limit the lifetime to very low values and therefore have to be avoided. If the emittance of one beam is substantially larger than the emittance of the other beam, particles with large amplitudes in the larger beam are sensitive to resonances of much higher order, in the SPS at least to order 16. This leads to a reduced lifetime and to unacceptable particle losses in the experimental areas