Paper  Title  Page 

TPAP057  BeamBeam Simulations for the eRHIC Electron Ring  3399 


Funding: Work performed under the auspices of the U.S. Department of Energy. To study collisions between polarized electrons and heavy ions or polarized protons at high energy, adding a 10 GeV electron storage ring to the existing RHIC facility is currently under consideration. To achieve high luminosities, vertical beambeam tuneshift parameters of 0.08 are required for the electron beam. Simulation studies are being performed to study the feasibility of these high tuneshift parameters and to explore the potential for even higher tuneshifts. Recent results of these studies are presented. 

TPAP058  BeamBeam Simulations for DoubleGaussian Beams  3405 


Funding: Work performed under the auspices of the U.S. Department of Energy. Electron cooling together with intrabeam scattering results in a transverse distribution that can best be described by a sum of two Gaussians, one for the highdensity core and one for the tails of the distribution. Simulation studies are being performed to understand the beambeam interaction of these doubleGaussian beams. Here we report the effect of lowfrequency random tune modulations on diffusion in doubleGaussian beams and compare the effects to those in beambeam interactions with regular Gaussian beams and identical tuneshift parameters. 

TPAT076  Measurement of the LuminousRegion Profile at the PEPII IP, and Application to e± BunchLength Determination  3973 


The threedimensional luminosity distribution at the interaction point (IP) of the SLAC BFactory is measured continuously, using e^{+}e^{} –> e^{+}e^{} and e+e –> mu+mu events reconstructed online in the silicon tracker of the BaBar detector. The centroid of the transverse luminosity profile provides a very precise and reliable monitor of medium and longterm orbit drifts at the IP. The longitudinal centroid is sensitive to variations in the relative RF phase of the colliding beams, both over time and differentially along the bunch train. The measured horizontal r.m.s. width of the distribution is consistent with a sizeable dynamicbeta effect; it is also useful as a benchmark of strongstrong beambeam simulations. The longitudinal luminosity distribution depends on the e± bunch lengths and vertical IP betafunctions, which can be different in the high and lowenergy rings. Using independent estimates of the betafunctions, we analyze the longitudinal shape of the luminosity distribution in the presence of controlled variations in accelerating RF voltage and/or beam current, to extract separate measurements of the e^{+} and e^{} bunch lengths.  
TPAT077  BeamBeam Study on the Upgrade of Beijing Electron Positron Collider  4000 


It is an important issue to study the beambeam interaction in the design and performance of such a high luminosity collider as BEPCII, the upgrade of Beijing Electron Positron Collider. The weakstrong simulation is generally used during the design of a collider. For performance a large scale tune scan, the weakstrong simulation studies on beambeam interaction were done, and the geometry effects were taken into account The strongstrong simulation studies were done for investigating the luminosity goal and the dependence of the luminosity on the beam parameters.  
TPAT078  Coherent BeamBeam Modes in the CERN Large Hadron Collider (LHC) for Multiple Bunches, Different Collisions Schemes and Machine Symmetries  4030 


In the LHC almost 3000 bunches in each beam will collide near several experimental regions and experience headon as well as long range beambeam interactions. In addition to single bunch phenomena, coherent bunch oscillations can be excited. Due to the irregular filling pattern and the unsymmetric collision scheme, a large number of possible modes must be expected, with possible consequences for beam measurements. To study these effects, a simulation program was developped which allows to evaluate the interaction of many bunches. It is flexible enough to easily implement any possible bunch configuration and collision schedule and also to study the effect of machine imperfections such as optical asymmetries. First results will be presented and future developments are discussed.  
TPAT079  Importance of the Linear Coupling and Multipole Compensation of LongRange BeamBeam Interactions In Tevatron  4039 


Funding: The US Department of Energy under Grant No. DEFG0204ER41288. In Tevatron, serious longrange beambeam effects are due to many parasitic collisions that are distributed around the ring. Because of this nonlocalized nature of longrange beambeam interactions, the multipole compensation with oneturn or sectional maps aims a global compensation of longrange beambeam interactions. Since nonlinear beam dynamics in a storage ring can usually be described by a oneturn map that contains all global information of system nonlinearities, by minimizing nonlinear terms of the maps orderbyorder with a few groups of multipole correctors, one could reduce the nonlinearity globally. Since a large beam separation is typical at parasitic points, in the phasespace region that is relevant to the beam, longrange beambeam interactions can be expanded into a Taylor series around the beam separation and be included into the oneturn map for the global compensation. To examine the effect of this multipole compensation scheme, the emittance growth of both p and pbar beam in Tevatron were studied with a beambeam simulation. The result showed that the multipole compensation can significantly reduces the emittance growth of the pbar beam due to longrange beambeam interactions. 

TPAT081  Observation of ElectronIon Effects at RHIC Transition  4087 


Funding: Work performed under the auspices of the U.S. Department of Energy. Electron cloud is found to be a serious obstacle on the upgrade path of the Relativistic Heavy Ion Collider (RHIC). At twice the design number of bunches, electronion interactions cause significant instability, emittance growth, and beam loss along with vacuum pressure rises when the beam is accelerated across the transition. 

TPAT083  Computational Study of the BeamBeam Effect in Tevatron Using the LIFETRAC Code  4117 


Funding: Work supported by the Universities Research Assos., Inc., under contract DEAC0276CH03000 with the U.S. Dept. of Energy. Results of a comprehensive numerical study of the beambeam effect in the Tevatron are presented including the dependence of the luminosity lifetime on the tunes, chromaticity and optics errors. These results help to understand the antiproton emittance blowup routinely observed in the Tevatron after the beams are brought into collision. To predict a long term luminosity evolution, the diffusion rates are increased to represent long operation time (~day) by using a small number of simulated turns. To justify this approach, a special simulation study of interplay between nonlinear beambeam resonances and diffusion has been conducted. A number of ways to mitigate the beambeam effects are discussed, such as increasing bunch spacing, separation between the beams and beambeam compensation with electron lenses. 

TPAT084  LIFETRAC Code for the WeakStrong Simulation of the BeamBeam Effect in Tevatron  4138 


Funding: Work supported by the Universities Research Assos., Inc., under contract DEAC0276CH03000 with the U.S. Dept. of Energy. A package of programs for weakstrong simulation of beambeam effects in hadron colliders is described. Accelerator optics parameters relevant to the simulation are derived from beam measurements and calculations are made using OptiM optics code. The key part of the package is the upgraded version of the LIFETRAC code which now includes 2D coupled optics, chromatic modulation of betafunctions, nonGaussian shape of the strong bunches and nonlinear elements for beambeam compensation. Parallel computations are used and in the case of the Tevatron (2 main IPs + 70 parasitic IPs) the code has a productivity of ~1·10^{10} particles*turns/day on a 32node cluster of Pentium IV 1.8 GHz processors. 

TPAT085  Development of a BeamBeam Simulation Code for e^{+}e^{} Colliders  4176 


Funding: Chinese National Foundation of Natural Sciences, contract 10275079 JSPS Core University Program BEPC will be upgraded into BEPCII, and the luminosity will be about 100 times higher. We developed a three dimensional strongstrong PIC code to study the beambeam effects in BEPCII. The transportation through the arc is the same as that in Hirata's weakstrong code. The beambeam force is computed directly by solving the Poisson equation using the FACR method, and the boundary potential is computed by circular convolution. The finite bunch length effect is included by longitudinal slices. An interpolation scheme is used to reduce the required slice number in simulations. The standard message passing interface (MPI) is used to parallelize the code. The computing time increases linearly with (n+1), where n is the slice number. The calculated luminosity of BEPCII at the design operating point is less than the design value. The best area in the tune space is near (0.505,0.57) according to the survey, where the degradation of luminosity can be improved. 