An Investigation of the `Flip-Flop' Beam-Beam Effect in SPEAR

When colliding electron and positron bunches in SPEAR at high values of the beam-beam tune shift parameter Δν, it had been observed that sometimes one of the equal intensity beams would blow up in the vertical plane more than the other beam. It was subsequently found that a small adjustment to the phase difference between the RF accelerating cavities would make the beam `flip' the other way. The results of the investigation of this phenomenon are presented in this paper.