Measurement and Simulation of Electron Cloud Induced Emittance Growth at Cesrta

This paper presents recent observations obtained on the study of electron cloud induced instabilities and emittance growth on positron beams at the Cornell Electron-Positron Storage Ring Test Acceleartor (CesrTA), and the simulation of these phenomena under similar beam conditions using the program CMAD. Results show that the transition to large bunch oscillations ocurrs at similar electron cloud densities in experiments as well as simulations. Beam size measurements were carried out using an x-ray beam size monitor (xBSM). The spectrum of the motion of the bunches were recorded using beam position monitors. The experiment consisted of using a train of positron bunches to generate the electron cloud, and observation of a “witness bunch" at different positions behind the train. Motion of the bunches in the train were controlled using feedback, thus suppressing multi-bunch effects. This experimental set up was suitable for comparison with simulations because the simulations were carried out only to study single bunch effects.