Using passive cavities for bunch shortening in CESR

Passive (beam-driven) superconducting cavities can be used in storage rings for bunch shortening when necessary high RF voltage can be achieved only by using multiple cavities, but the beam power consumption does not justify using all of them in the active mode, powered by klystrons. An example is the e/sup +/e/sup -/ collider CESR running with a beam energy below 2.5 GeV as a charm-tau factory (CESR-c). A short bunch length of about 10 mm is required for obtaining higher luminosity, while maximum beam power is only 160 kW. Theoretical and experimental studies are in progress at CESR to investigate the collider performance at low energy in preparation for its conversion to CESR-c. In the course of these studies we looked at possible impacts of using passive cavities on the accelerator performance. The results are presented.