Turbulent bunch lengthening and the microwave instability

Presents an analysis of single-bunch oscillations which leads to instability above a certain threshold current. It is essentially caused by the coupling of positive and negative mode numbers of the same bunch-shape oscillation. It can be driven by resonant impedances such as the fundamental mode of the RF cavities or the broad band impedance due to a larger number of resonances in the RF cavities and the vacuum chamber. These exist in every storage ring or accelerator, and no unphysical impedances are thus required to provide coupling. (14 refs).