Electron cloud studies for KEKB

Electron-cloud build up, incoherent tune spread and electron-induced beam instability are likely to be responsible for the vertical beam-size increase observed at the KEKB Low Energy Ring (LER). We report on recent simulations and analytical estimates, addressing the electron-cloud evolution for various magnet configurations, comparing the beam size blow up predicted by three different simulation models (micro-bunches, multi-particle tracking with soft Gaussian approximation, particle-in-cell), and finally discussing analytical expressions for the instability threshold.