Simulation study of electron cloud multipacting in straight sections of PEP-II

Simulation studies of electron cloud multipacting were performed for the SLAC B-factory vacuum chamber for different bunch trains and solenoidal magnetic field. Results show that increasing the number of positron bunches by a factor of two and keeping the same current per bunch means that the solenoidal field needs to be doubled in order to keep the same electron cloud density. Fortunately there are regions that are "free of multipacting" at smaller values of field where the electron cloud density can not get very high. To build the electron cloud, positron bunches have to lose some amount of their kinetic energy through the longitudinal electric field. When the cloud is already established, this longitudinal field acts as an oscillating force. This action is similar to the action of RF fields in a cavity. As a result the positron bunches will have different lengths throughout the train.