Calculation of Impedance from Multibunch Synchronous Phases: Theory and Experimental Results [report]

Shyam Prabhakar
1998 unpublished
A novel beam-based method for measuring the longitudinal impedance spectrum is demonstrated using experimental data from the PEP-II High Energy Ring (HER). The method uses a digital longitudinal feedback system from which the charge and synchronous phase are measured for every bucket. Calculation of the transfer function from fill shape to synchronous phase yields the impedance seen by the beam at revolution harmonics. The experimentallyderived longitudinal impedance function and lab
more » ... s of the impedance of parked RF cavities are compared to suggest a mechanism for the occasional instability of low-order coupled bunch modes observed in the HER during commissioning in October 1997.
doi:10.2172/9945 fatcat:sjdnwk3txfdmdbyaqptusltisi