Numerical modeling of beam-environment interactions in the PEP-II B-Factory

The PEP-II B-Factory is designed to operate at high currents with many bunches (1658) to achieve the luminosity required for physics studies. Interactions of a beam with its environment in a storage ring raise various issues of concern for accelerator physics, mechanical design and device performance. First, for accelerator physics, wakefields generated by interactions of a beam with beamline components, if not properly controlled, will drive single-bunch and coupled-bunch instabilities. The total broad-band impedance of the ring cannot exceed a budget limited by single-bunch effects. The growth rate of a coupled-bunch mode contributed from narrow-band impedance should be smaller than the damping rate due to synchrotron radiation; otherwise, suppression by feedback control will be necessary. Second, the energy loss by a beam at a beamline component in the form of higher-order-mode (HOM) power leads to additional heating on the component, and to TE mode radiation through openings on vacuum chamber walls. Last, calculations of transfer and beam impedances of pickup and kicker devices are essential for improving their performance and for identifying trapped modes. To address these issues quantitatively requires numerical simulations of each beamline component which include the realistic geometry and the relevant physics involved in the particular beam-environment interactions.