Coupled Bunch Instability Caused by an Electron Cloud

Coupled bunch instability caused by electron cloud has been observed in the KEKB-LER. Time evolution of the instabilities just after the turning-off the transverse bunch feedback have been recorded with several solenoid-field conditions to suppress the blowup due to electron cloud. The mode spectra of the coupled-bunch instabilities have been compaired with the simulations of electrons moving in drift space, weak solenoid field and strong bending field.