Beam interaction with elements of an accelerator can be a reason for instabilities, causing a limited beam performance. Improving the vacuum chamber design and reducing the impedance by orders of magnitude increases the intensity threshold for impedance instability; then the two-stream effects due to beam interaction with secondary plasma impose new limitations on beam intensity and brightness. Electron beams are perturbed by the accumulated positive ions. Proton and positron beams can be effected by the electrons or negative ions generated by the beam. These secondary particles can induce strong instabilities. The instabilities become more severe in high current operated accelerators and storage rings at small bunch spacing. Beam instabilities due to electrons were first observed for coasting proton beam or long proton bunches at the Novosibirsk INP, CERN ISR and Los Alamos PSR. Recently the two-stream instability was observed in almost all the storage rings at high beam intensity. Observations of the two-stream instability at different conditions will be reviewed. Beam performance limitation, diagnostics and possibilities to damp the two-stream instability will be discussed.


Talk Slides: slides