Commissioning experience from PEP-II HER longitudinal feedback
The DSP-based bunch-by-bunch feedback system installed in the PEP-II HER has been used to damp HOM-induced instabilities at beam currents up to 6-5 mA during commissioning. Beam pseudospectra calculated from feedback system data indicate the presence of coupled bunch modes that coincide with the 0-M-2 cavity HOM. 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*frev 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 time variation due to the cavity transient is shown to be large enough to result in Landau damping of coupled bunch modes.
- Research Organization:
- Stanford Univ., Stanford Linear Accelerator Center, CA (US)
- Sponsoring Organization:
- USDOE Office of Energy Research, Washington, DC (US)
- DOE Contract Number:
- AC03-76SF00515
- OSTI ID:
- 674792
- Report Number(s):
- SLAC-PUB--7849; CONF-980573--; ON: DE98059235
- Country of Publication:
- United States
- Language:
- English
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