| Paper |
Title |
Page |
| MOPLS051 |
Tracking Down a Fast Instability in the PEP-II LER
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658 |
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- U. Wienands, R. Akre, S.C. Curry, S. DeBarger, F.-J. Decker, S. Ecklund, A.S. Fisher, S.A. Heifets, A. Krasnykh, A. Kulikov, A. Novokhatski, J. Seeman, M.K. Sullivan, D. Teytelman, D. Van Winkle, G. Yocky
SLAC, Menlo Park, California
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During Run 5, the beam in the PEP-II Low Energy Ring (LER) became affected by a predominantly vertical instability with very fast growth rate of 10…60/ms - much faster than seen in controlled grow-damp experiments - and varying threshold. The coherent amplitude of the oscillation was limited to approx. 1 mm pk-pk or less and would damp down over a few tens of turns; however, beam loss set in even as the measured amplitude damped, causing a beam abort. This led to the conclusion that the beam was actually blowing up. The presence of a 2 nu_s line in the spectrum suggested a possible head-tail nature of the instability, although chromaticity was not effective in raising the threshold. In this paper we will describe the measurements and data taken to isolate and locate the cause of the instability and, eventually, the discovery and fix of the root cause.
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| THPCH099 |
A Turn-by-turn, Bunch-by-bunch Diagnostics System for the PEP-II Transverse Feedback Systems
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3026 |
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- R. Akre, W.S. Colocho, A. Krasnykh, V. Pacak, R. Steele, U. Wienands
SLAC, Menlo Park, California
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A diagnostics system centered around commercial fast 8-bit digitizer boards has been implemented for the transverse feedback systems at PEP-II. The boards can accumulate bunch-by-bunch position data for 4800 turns (35 ms) in the x plane and the y plane. A dedicated trigger chassis allows to trigger the data acquisition on demand, or on an injection shot to diagnose injection problems, and provides gating signals for grow-damp measurements. Usually, the boards constantly acquire data and a beam abort stops data acquitision, thus preserving the last 4800 turns of position information before a beam abort. Software in a local PC reads out the boards and transfers data to a fileserver. Matlab-based data analysis software allows to present the raw data but also higher-level functions like spectra, modal analysis, spectrograms and other functions. The system has been instrumental in diagnosing beam instabilities in PEP. This paper will describe the architecture of the system and its applications.
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| THPCH103 |
Design and Testing of Gproto Bunch-by-bunch Signal Processor
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3038 |
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- D. Teytelman, R. Akre, J.D. Fox, A. Krasnykh, C.H. Rivetta, D. Van Winkle
SLAC, Menlo Park, California
- A. Drago
INFN/LNF, Frascati (Roma)
- J.W. Flanagan, T. Naito, M. Tobiyama
KEK, Ibaraki
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A prototype programmable bunch-by-bunch signal acquisition and processing channel with multiple applications in storage rings has been developed at SLAC. The processing channel supports up to 5120 bunches with bunch spacings as close as 1.9 ns. The prototype has been tested and operated in five storage rings: SPEAR-3, DAFNE, PEP-II, KEKB, and ATF damping ring. The testing included such applications as transverse and longitudinal coupled-bunch instability control, bunch-by-bunch luminosity monitoring, and injection diagnostic. In this contribution the prototype design will be described and its operation will be illustrated with the data measured at the abovementioned accelerators.
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