Performance of a Correlator Filter in Betatron Tune Measurements and Damping on the NSLS Booster

A "compensated correlator filter", described by Kramer, et al.[1] has been used for measurement and damping of betatron oscillations in the NSLS booster. The filter consists of a zero-degree power splitter, a 180-degree splitter, a length of 7/8" air dielectric coaxial cable, and a short length of RG-58 cable. Connected to a beam position monitor, the output of the filter is proportional to the difference in transverse position of each bunch on subsequent turns. The useful bandwidth of the filter for damping rigid bunch oscillations extends from 10 MHz to 250 MHz, in contrast with the gigahertz bandwidth requirements for stochastic cooling, for which the filter was originally proposed. Attenuation of all rotation harmonics in this bandwidth is 40-60 dB.