A TRAPPED PHOTOELECTRON INSTABILITY IN ELECTRON AND POSITRON STORAGE-RINGS

An anomalous growth of the horizontal coupled bunch modes of the bunch ed beam is observed in the Cornell Electron Storage Ring. In contrast with instabilities caused by electromagnetic wake fields, the growth r ate is a highly nonlinear function of the bunch charge. We show that t his effect is due to photoelectrons produced by synchrotron radiation which are trapped in the beam chamber by the bending magnet field and a quadrupole electrostatic field. We have developed a numerical simula tion and an analytical model of this process. [S0031-9007(97)04354-8].