Abstracts Brochure - CERN

MOPLS — Poster Session 26-Jun-06 16:00 - 18:00
elements have been implemented in MAD-X to allow the full PTC description of the machine. It is discussed how
this real PTC model differs from the ’fake’ MAD-X model and how well PTC describes the real machine.
Longitudinal Beam Stability at the Cornell Electron-positron Storage Ring
The Cornell Electron-Positron Storage Ring
(CESR) is operated at high energy, 5.3 GeV
per beam, as a synchrotron source, and at
low energy, 1.9 GeV, for high energy physics.
R. Holtzapple, P.J.S. Stonaha (Alfred University) B. Cerio (Colgate
University)
The longitudinal beam dynamics at these two different operating energies is significant. Measurements of single and
multiple train longitudinal beam stability of the bunches have been performed using a dual sweep streak camera and
are presented in this paper.
Studies of the Long-range Beam-beam Interaction at CESR
The Cornell Electron Storage Ring facility
operates 2-GeV multi-bunch electron and
positron beams in a single beam-pipe. Electrostatic
separators are used to separate the
J.A. Crittenden (Cornell University, Department of Physics) M.G.
Billing (CESR-LEPP)
two counter-rotating beams at the parasitic crossings. When the beam energy was lowered from 5 GeV in 2003,
the strength of the beam-beam interaction became a more important factor in beam-current limitations, resulting in
extensive experimental and calculational studies of their characteristics. The CESR lattice design procedure has been
modified recently to account explicitly for their dynamic consequences. We describe our modelling of the beam-beam
interaction, experimental validation techniques, and investigations into compensation strategies.
Luminosity Variations along Bunch Trains in PEP-II
In spring of 2005 after a long shut-down,
the luminosity of the B-Factory PEP-II decreased
along the bunch trains by about 25-
30%. There were many reasons studied
F.-J. Decker, M. Boyes, W.S. Colocho, A. Novokhatski, M.K. Sullivan,
J.L. Turner, S.P. Weathersby, U. Wienands, G. Yocky (SLAC)
which could have caused this performance degradation, like a bigger phase transient due to an additional RF station
in the Low-Energy-Ring (LER), bad initial vacuum, electron cloud, chromaticity, steering, dispersion in cavities, beam
optics, etc. The initial specific luminosity of 4.2 sloped down to 3.2 and even 2.8 for a long train (typical: 130 of 144),
later in the run with higher currents and shorter trains (65 of 72) the numbers were more like 3.2 down to 2.6. Finally
after steering the interaction region for an unrelated reason (overheated BPM buttons) and the consequential lower
luminosity for two weeks, the luminosity slope problem was mysteriously gone. Several parameters got changed and
there is still some discussion about which one finally fixed the problem. Among others, likely candidates are: the
LER betatron function in x at the interaction point got reduced, making the LER x stronger, dispersion reduction in
the cavities, and finding and fixing a partially shorted magnet.
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