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Alexahin, Y.

Paper Title Page
MOPA006 Theory and Reality of Beam-Beam Effects at Hadron Colliders 544
 
  • Y. Alexahin
    Fermilab, Batavia, Illinois
 
  The beam-beam phenomena in hadron colliders is just as rich as in e+e- machines: orbit and focusing perturbations, excitation of nonlinear resonances, coherent tuneshifts. Moreover, the absence of radiation damping and long duration of a store permit even high-order (and correspondingly weak) resonances to manifest themselves presenting a major challenge for both theoretical analysis and machine operation. The recent progress in understanding of and coping with the beam-beam effects at hadron colliders, primarily at the Tevatron, is discussed.  
MPPE052 Study on Coupling Issues in the Recycler at Fermilab 3209
 
  • M. Xiao, Y. Alexahin, D.E. Johnson, M.-J. Yang
    Fermilab, Batavia, Illinois
 
  We have been working and trying to answer the following questions: where are the coupling sources in the Recycler and is the existing correcting system working fine? In this paper, we report the analysis on the sources from both modeling by code MAD based on nonlinear lattice and real machine. From the first turn flesh orbit, we fit the off-plane orbits by third order polynomial, then separate 1st, 2nd and 3rd order coefficients to see different effects. On the other hand, we present the analysis from turn by turn data, which is to verify the phase of two skew quads families are more or less orthogonal, and to make sure the minimum tune split is small enough, and is consistent with the measurement.  
MPPP042 Landau Damping of the Weak Head-Tail Instability at Tevatron 2714
 
  • P.M. Ivanov, Y. Alexahin, J. Annala, V. Lebedev, V.D. Shiltsev
    Fermilab, Batavia, Illinois
 
  Landau damping of the head-tail modes in Tevatron beam with the help of octupole-generated betatron tune spreads permits to reduce chromaticity from 15-20 units to zero thus significantly improving the beam lifetime. The octupole strengths have been experimentally optimized at different stages of the Tevatron operation, from proton injection to collision. Predictions of the analytical Landau damping model are compared with the experimental results.  
MPPP043 Betatron Tune Spread Generation and Differential Chromaticity Control by Octupole at Tevatron 2756
 
  • P.M. Ivanov, Y. Alexahin, J. Annala, V. Lebedev
    Fermilab, Batavia, Illinois
 
  Application of octupoles for Landau damping of the unstable head-tail modes requires careful consideration at their combination into separate families to insure maximum effectiveness and avoid degradation of the dynamic aperture due to the non-linear magnetic fields. Existing octupolar magnets around the machine have been arranged into four functional families with individual power supplies. Two of these families generate betatron tune spreads in the vertical and horizontal planes whereas the other two control the differential chromaticity between the proton and antiproton helices. The calculated effect on tunes and chromaticity is compared with direct measurements. Analytical formulas for betatron tune spectral density functions are presented.  
TPAP026 Improving the Tevatron Collision Helix 1931
 
  • R. Moore, Y. Alexahin, J.A. Johnstone, T. Sen
    Fermilab, Batavia, Illinois
 
  In the Tevatron, protons and pbars circulate in a single beam pipe, so electrostatic separators are used to create helical orbits that separate the two beams except at the two interaction points (IP). Increasing the separation outside of the IPs is desirable in order to decrease long range beam-beam effects during high energy physics (HEP) stores. We can increase separation by running the separators at higher gradients or by installing additional separators. We are pursuing both strategies in parallel. Here, we describe Tevatron operation with higher separator gradients and with new separators installed during a recent shutdown. We also describe possible future improvements.  
TPAP032 Beam-beam Effects in the Tevatron Run II 2245
 
  • V.D. Shiltsev, Y. Alexahin, V. Lebedev, P. Lebrun, R. Moore, T. Sen, A. Valishev, X. Zhang
    Fermilab, Batavia, Illinois
 
  Funding: Work supported by the Universities Research Assos., Inc., under contract DE-AC02-76CH03000 with the U.S. Dept. of Energy.

The Tevatron in Collider Run II (2001-present) is operating with many times higher beam intensities and luminosities than in previous Run I (1992-1995). Electromagnetic long-range and head-on interactions of high intensity proton and antiproton beams have been significant sources of beam loss and lifetime limitations. We present observations of the beam-beam phenomena in the Tevatron and results of relevant beam studies. We analyze the data and various methods employed in operations, predict the performance at upgraded beam parameters and luminosity and discuss possible improvements.

 
TPAT083 Computational Study of the Beam-Beam Effect in Tevatron Using the LIFETRAC Code 4117
 
  • A. Valishev, Y. Alexahin, V. Lebedev
    Fermilab, Batavia, Illinois
  • D.N. Shatilov
    BINP SB RAS, Novosibirsk
 
  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.

 
TPAT084 LIFETRAC Code for the Weak-Strong Simulation of the Beam-Beam Effect in Tevatron 4138
 
  • A. Valishev, Y. Alexahin, V. Lebedev
    Fermilab, Batavia, Illinois
  • D.N. Shatilov
    BINP SB RAS, Novosibirsk
 
  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.