| Paper | Title | Page |
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| TPAP057 | Beam-Beam Simulations for the eRHIC Electron Ring | 3399 |
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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 beam-beam 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. |
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| TPAP058 | Beam-Beam Simulations for Double-Gaussian Beams | 3405 |
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Funding: Work performed under the auspices of the U.S. Department of Energy. Electron cooling together with intra-beam scattering results in a transverse distribution that can best be described by a sum of two Gaussians, one for the high-density core and one for the tails of the distribution. Simulation studies are being performed to understand the beam-beam interaction of these double-Gaussian beams. Here we report the effect of low-frequency random tune modulations on diffusion in double-Gaussian beams and compare the effects to those in beam-beam interactions with regular Gaussian beams and identical tuneshift parameters. |
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| TPAT076 | Measurement of the Luminous-Region Profile at the PEP-II IP, and Application to e± Bunch-Length Determination | 3973 |
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| The three-dimensional luminosity distribution at the interaction point (IP) of the SLAC B-Factory 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 long-term 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 dynamic-beta effect; it is also useful as a benchmark of strong-strong beam-beam simulations. The longitudinal luminosity distribution depends on the e± bunch lengths and vertical IP beta-functions, which can be different in the high- and low-energy rings. Using independent estimates of the beta-functions, 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 | Beam-Beam Study on the Upgrade of Beijing Electron Positron Collider | 4000 |
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| It is an important issue to study the beam-beam interaction in the design and performance of such a high luminosity collider as BEPCII, the upgrade of Beijing Electron Positron Collider. The weak-strong simulation is generally used during the design of a collider. For performance a large scale tune scan, the weak-strong simulation studies on beam-beam interaction were done, and the geometry effects were taken into account The strong-strong simulation studies were done for investigating the luminosity goal and the dependence of the luminosity on the beam parameters. | ||
| TPAT078 | Coherent Beam-Beam Modes in the CERN Large Hadron Collider (LHC) for Multiple Bunches, Different Collisions Schemes and Machine Symmetries | 4030 |
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| In the LHC almost 3000 bunches in each beam will collide near several experimental regions and experience head-on as well as long range beam-beam 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 Long-Range Beam-Beam Interactions In Tevatron | 4039 |
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Funding: The US Department of Energy under Grant No. DE-FG02-04ER41288. In Tevatron, serious long-range beam-beam effects are due to many parasitic collisions that are distributed around the ring. Because of this non-localized nature of long-range beam-beam interactions, the multipole compensation with one-turn or sectional maps aims a global compensation of long-range beam-beam interactions. Since nonlinear beam dynamics in a storage ring can usually be described by a one-turn map that contains all global information of system nonlinearities, by minimizing nonlinear terms of the maps order-by-order 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 phase-space region that is relevant to the beam, long-range beam-beam interactions can be expanded into a Taylor series around the beam separation and be included into the one-turn 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 beam-beam simulation. The result showed that the multipole compensation can significantly reduces the emittance growth of the pbar beam due to long-range beam-beam interactions. |
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| TPAT081 | Observation of Electron-Ion Effects at RHIC Transition | 4087 |
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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, electron-ion interactions cause significant instability, emittance growth, and beam loss along with vacuum pressure rises when the beam is accelerated across the transition. |
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| TPAT083 | Computational Study of the Beam-Beam Effect in Tevatron Using the LIFETRAC Code | 4117 |
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Funding: Work supported by the Universities Research Assos., Inc., under contract DE-AC02-76CH03000 with the U.S. Dept. of Energy. Results of a comprehensive numerical study of the beam-beam 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 blow-up 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 beam-beam resonances and diffusion has been conducted. A number of ways to mitigate the beam-beam effects are discussed, such as increasing bunch spacing, separation between the beams and beam-beam compensation with electron lenses. |
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| TPAT084 | LIFETRAC Code for the Weak-Strong Simulation of the Beam-Beam Effect in Tevatron | 4138 |
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Funding: Work supported by the Universities Research Assos., Inc., under contract DE-AC02-76CH03000 with the U.S. Dept. of Energy. A package of programs for weak-strong simulation of beam-beam 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 beta-functions, non-Gaussian shape of the strong bunches and non-linear elements for beam-beam compensation. Parallel computations are used and in the case of the Tevatron (2 main IPs + 70 parasitic IPs) the code has a productivity of ~1·1010 particles*turns/day on a 32-node cluster of Pentium IV 1.8 GHz processors. |
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| TPAT085 | Development of a Beam-Beam Simulation Code for e+e- Colliders | 4176 |
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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 strong-strong PIC code to study the beam-beam effects in BEPCII. The transportation through the arc is the same as that in Hirata's weak-strong code. The beam-beam 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. |