PAC09 - List of Authors (Weathersby, S.P.)

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Weathersby, S.P.

Paper	Title	Page
TH5PFP088	HOM Sensitivity in the PEP-II HER Vacuum Chamber	3413
	S.P. Weathersby, A. Novokhatski, M.K. Sullivan SLAC, Menlo Park, California
	Funding: Work supported by Department of Energy Contract DE-AC02-76SF00515 Synchrotron radiation is the main source of vacuum chamber heating in the PEP-II storage ring collider. This heating is reduced substantially as lattice energy is lowered. Energy scans over Υ energy states were performed by varying the high energy ring (HER) lattice energy at constant gap voltage and frequency. We observed unexpected temperature rise at particular locations when HER lattice energy was lowered from 8.6 GeV (Υ(3S)) to 8.0 GeV (Υ(2S)) while most other temperatures decreased. Bunch length measurements reveal a shorter bunch at the lower energy. The shortened bunch overheated a beam position monitoring electrode causing a vacuum breach. We explain the unexpected heating as a consequence of increased higher order mode (HOM) power generated by a shortened bunch. In this case, temperature rise helps to identify HOM sources and HOM sensitive vacuum chamber elements. Reduction of gap voltage helps to reduce this unexpected heating.

Paper

Title

Page

TH5PFP088

HOM Sensitivity in the PEP-II HER Vacuum Chamber

3413

S.P. Weathersby, A. Novokhatski, M.K. Sullivan
SLAC, Menlo Park, California

Funding: Work supported by Department of Energy Contract DE-AC02-76SF00515

Synchrotron radiation is the main source of vacuum chamber heating in the PEP-II storage ring collider. This heating is reduced substantially as lattice energy is lowered. Energy scans over Υ energy states were performed by varying the high energy ring (HER) lattice energy at constant gap voltage and frequency. We observed unexpected temperature rise at particular locations when HER lattice energy was lowered from 8.6 GeV (Υ(3S)) to 8.0 GeV (Υ(2S)) while most other temperatures decreased. Bunch length measurements reveal a shorter bunch at the lower energy. The shortened bunch overheated a beam position monitoring electrode causing a vacuum breach. We explain the unexpected heating as a consequence of increased higher order mode (HOM) power generated by a shortened bunch. In this case, temperature rise helps to identify HOM sources and HOM sensitive vacuum chamber elements. Reduction of gap voltage helps to reduce this unexpected heating.