Abstracts Brochure - CERN

MOPLS052
MOPLS053
MOPLS054
26-Jun-06 16:00 - 18:00 MOPLS — Poster Session
the measurements and data taken to isolate and locate the cause of the instability and, eventually, the discovery and
fix of the root cause.
Luminosity Improvement at PEP-II Based on Optics Model and Beam-beam Simulation
Y. Cai, F.-J. Decker, J. Seeman, K.G. Sonnad, U. Wienands, Y.T. Yan
(SLAC)
122
The model independent analysis (MIA) has
been successfully used at PEP-II to understand
machine optics and improve the luminosity.
However, the rate of success was lim-
ited because the improvement of optics does not necessarily lead to increase of luminosity. Recently, we were able to
reconstruct MIA model in a full optics code, LEGO, and used it to calculate complete lattice and beam parameters.
These parameters were fed to the beam-beam code, BBI, to understand the luminosity histories at PEP-II over the
past year. Using these tools, we optimized the luminosity by varying the beam parameters such as emittance. Finally,
we implemented an optimized solution with a set of asymmetric horizontal orbit bumps into the machines during a
delivery shift with a few percentage gain in luminosity. The solution was retained at PEP-II machines along with the
luminosity. Later, these asymmetric bumps also played a vital role in reaching 1x10 34 cm-2s-1 as the beam currents
increased.
Beta-beat Correction Using Strong Sextupole Bumps in PEP-II
A method for correcting lattice beta mis-
G. Yocky (SLAC)
matches has been developed for the PEP-
II collider using orbit offsets in strong sextupoles.
The solution is first predicted in the MAD program by modeling closed orbit bumps in the plane of
correction at the sextupoles strongest in that plane. The derived solution is then tested in the machine to confirm the
prediction and finally dialed into the machine under high-current conditions.
On Increasing the HERA Luminosity
The luminosity of the HERA lepton proton
Y.A. Kot (DESY)
collider is limited in part by the bunch length
of the protons of 20cm. This limitation is
expected to be removed by the installation of a new damper system which will control longitudinal coupled bunch
instabilities of the proton beam and avoid the bunch lengthening of a factor of two. This opens the possibility for
increasing the luminosity HERA since the beta functions at IP for both leptons and protons can be lowered by about
20% without noticeable reduction of the corresponding luminosity by the so-called hour-glass effect. The beam spot
size can be further reduced if the beam-beam focusing of the leptons (dynamic beta) at IP is increased by softening the
rigorous beam beam-beta beat compensation which is accomplished by proper phasing of the two IP’s. Unfortunately
the non-linear chromaticity compensation would be weakened as well, which will cause an enhancement of the
synchro-betatron resonances and may lead to poor lifetime and poor background conditions. Therefore, the nonlinear
chromaticity needs to be reduced by means of a more complex scheme of chromaticity compensating sextupole
magnets.