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Title |
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| THPLT155 |
Development and Testing of a Low Group-delay Woofer Channel for PEP-II
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2819 |
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- J.D. Fox, L. Beckman, D. Teytelman, D. Van Winkle, A. Young
SLAC, Menlo Park, California
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The PEP-II HER and LER require active longitudinal feedback to control coupled-bunch instabilities. The PEP-II RF systems use direct and comb loop feedback to reduce the cavity fundamental impedance, though the remaining low-mode impedance is providing the fastest growing unstable modes in both rings. Since commissioning the longitudinal feedback systems have used a dedicated "woofer" channel to apply the low-frequency correction kick via the RF system. The performance of this original controller is limited by the maximum gain that can be supported due to the processing delay (group delay), as well as the difficulty in configuring a common correction controller that acts via two correction paths. A dedicated low-mode signal processing system has been developed to allow higher damping rates. It is a digital processing channel, operating at a 10 MHz sampling rate, and implementing flexible 5 to 10 tap FIR control filters. The design of the channel and initial control filters is presented, as are initial machine experiments quantifying the damping and noise floor of this low group delay woofer system.
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