Abstracts Brochure - CERN

MOPLS — Poster Session 26-Jun-06 16:00 - 18:00
2.2A in the low and high energy rings, respectively. Using the beam-beam code BBI, we systematically optimized the
luminosity and showed that a luminosity of over 2x10 34 cm-2s-1 is achievable within the limits of machine parameters.
Anomalous High Radiation Beam Aborts in the PEP-II B-factory
The PEP-II B-factory at SLAC has recently
experienced unexpected beam losses due
to anomalously high radiation levels at the
BaBar detector. The problem was finally
traced to the occurrence of very high pres-
M.K. Sullivan, S. Debarger, F.-J. Decker, S. Ecklund, A.S. Fisher,
S.M. Gierman, A. Kulikov, A. Novokhatski, J. Seeman, D. Teytelman,
U. Wienands (SLAC)
sure (>100 nTorr) spikes that have a very short duration (few seconds). We describe the events and show analysis
predicting where in the vacuum system the events originated and describe what was discovered in the vacuum
system.
Combined Phase Space Characterization at the PEP-II IP using Single-beam and Luminous-region
Measurements
We present a novel method to characterize
the e ± phase space at the IP of the SLAC Bfactory,
that combines single-beam measurements
with a detailed mapping of luminousregion
observables. Transverse spot sizes are
A. J. Bevan (Queen Mary University of London) A.S. Fisher, C.
O’Grady, J.M. Thompson, M. Weaver (SLAC) W. Kozanecki (CEA)
B.F. Viaud (Montreal University)
determined in the two rings with synchrotron-light monitors & extrapolated to the IP using measured lattice functions.
The 3-D luminosity distribution, as well as the spatial dependence of the transverse-boost distribution of the colliding
beams, are measured using e + e − –> mu+ mu- events reconstructed in the BaBar tracking detectors; they provide
information on the luminous spot size, the e − angular divergence & the vertical emittance. The specific luminosity,
which is proportional to the inverse product of the overlap IP beam sizes, is continuously monitored using Bhabhascattering
events. The combination of these measurements provide constraints on the horizontal & vertical spot sizes,
angular divergences, emittances & beta functions of both beams at the IP during routine high-luminosity operation.
Preliminary results of this combined-spot size analysis are confronted with measurements of IP beta-functions &
overlap IP beam sizes at low beam current.
Tracking Down a Fast Instability in the PEP-II LER
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 ampli-
U. Wienands, R. Akre, S.C. Curry, 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)
tude 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 nus 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
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