Commissioning experience from PEP-II HER longitudinal feedback
- Stanford Linear Accelerator Center, Stanford University, Stanford, California 94309 (United States)
The DSP-based bunch-by-bunch feedback system installed in the PEP-II high-energy ring (HER) has been used to damp instabilities induced by unwanted higher-order modes (HOMs) at beam currents up to 605 mA during commissioning. Beam pseudospectra calculated from feedback system data indicate the presence of coupled-bunch modes that coincide with a previously observed cavity mode (0-M-2). Bunch current and synchronous phase measurements are also extracted from the data. These measurements reveal the impedance seen by the beam at revolution harmonics. The impedance peak at 3{times}f{sub rev} indicates incorrect parking of the idle cavities, and explains the observed instability of mode 3. Bunch synchrotron tunes are calculated from lorentzian fits to the data. Bunch-to-bunch tune variation due to the cavity transient is shown to be large enough to result in Landau damping of coupled-bunch modes. {copyright} {ital 1998 American Institute of Physics.}
- Research Organization:
- Stanford Linear Accelerator Center
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC03-76SF00515
- OSTI ID:
- 365950
- Report Number(s):
- CONF-980573--
- Journal Information:
- AIP Conference Proceedings, Journal Name: AIP Conference Proceedings Journal Issue: 1 Vol. 451; ISSN 0094-243X; ISSN APCPCS
- Country of Publication:
- United States
- Language:
- English
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