Electron cloud effects on beam evolution in a circular accelerator

The interaction between a low-density electron cloud in a circular particle accelerator with a circulating charged particle beam is considered. The particle beam's space charge attracts the cloud, enhancing the cloud density near the beam axis. It is shown that this enhanced charge and the image charges associated with the cloud charge and the conducting wall of the accelerator may have important consequences for the dynamics of the beam propagation. The tune shift due to the electron cloud is obtained analytically and compared to a new numerical method (QUICKPIC) that is described here. Sample numerical results are presented and their significance for current and planned experiments is discussed. (23 refs).