Updated Impedance Estimate of the Pep-ii Rf Cavity

This paper presents an updated estimate of the higher-order mode impedance spectrum of the RF cavities for the PEP-II B-factory. The cavity is designed for continuous operation at 476 MHz with up to 150 kW wall dissipation and heavy beam loading. To reduce the growth rates of coupled-bunch instabilities the cavity higher-order modes are damped by three rectangular waveguides and broad-band loads. The results of detailed measurements on the first high-power cavity with all absorbers in place are presented and the damping effect due to the high-power coupler is discussed. Results are compared with earlier measurements of a cold-test model. Implications for the design of the broad-band bunch-by-bunch feedback systems and high-power HOM loads are discussed. Contributed to the 5th European Particle Accelerator Conference (EPAC 96) Sitges, Barcelona , Spain June 10-14, 1996 * Work supported by Department of Energy contract DE–AC03–76SF00515 (SLAC), DE-AC03-76SF00098 (LBNL). 2 UPDATED IMPEDANCE ESTIMATE OF THE PEP-II RF CAVITY* R.A. Rimmer, J. Byrd, M. Irwin, D.A. Goldberg, LBNL, Berkeley, CA, USA