Effect of synchrotron motion on the closed orbit distortion in crossing beams

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When beams collide with non-zero crossing angles, there is a dipole component to the beam-beam force, thus introducing a closed orbit distortion. If the force experienced by a particle is antisymmetric about the collision center, then the distorted orbit still passes through the collision center but with a changed slope, resulting in a shift from the nominal crossing angle. This antisymmetry in the force occurs for coasting beams, while for bunched beams, it is the case for particles at the center of the bunches, assuming that the bunches overlap exactly around the collision center. The presence of synchrotron motion means ... continued below

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Pages: 12

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Month, M. January 29, 1974.

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Description

When beams collide with non-zero crossing angles, there is a dipole component to the beam-beam force, thus introducing a closed orbit distortion. If the force experienced by a particle is antisymmetric about the collision center, then the distorted orbit still passes through the collision center but with a changed slope, resulting in a shift from the nominal crossing angle. This antisymmetry in the force occurs for coasting beams, while for bunched beams, it is the case for particles at the center of the bunches, assuming that the bunches overlap exactly around the collision center. The presence of synchrotron motion means that the beam- beam force experienced by a particle modulates as the particle moves back amd forth within the bunch. Specifically, a symmetric component to the force is introduced. If the synchrotron period is much longer tham the betatron period, the modulation of the force is adiabatic, and so the effect is a modulation of the closed orbit. The symmetric compoment of the dipole force causes; shift in the closed orbit at the collision center. This indicates a tendency for the beams to separate, which in turn changes the mature of the force between the two beams. The closed orbit shift is calculated. Some comments on self-consistency are made. It is indicated how under certain circumstances, a self-consistent solution may not exist. The case of SPEAR is considered. It is shown that for small crossing angles, the orbit shift at the collision center is larger than the beam size, indicating a major effect. Further-more, it is argued that a self-consistent solution cannot exist. For coasting beams, small angle crossings can be designed so that only the antisymmetric component of the dipole force is prcsemt. Thus, the predominant effect is a shift in the nominal crossing angle. (auth)

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Pages: 12

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Dep. NTIS

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  • Other Information: Orig. Receipt Date: 30-JUN-74

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  • Report No.: BNL--18578
  • Grant Number: None
  • DOI: 10.2172/4325968 | External Link
  • Office of Scientific & Technical Information Report Number: 4325968
  • Archival Resource Key: ark:/67531/metadc1023292

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Creation Date

  • January 29, 1974

Added to The UNT Digital Library

  • Oct. 15, 2017, 10:09 p.m.

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  • Oct. 25, 2017, 7:09 p.m.

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Month, M. Effect of synchrotron motion on the closed orbit distortion in crossing beams, report, January 29, 1974; Upton, New York. (digital.library.unt.edu/ark:/67531/metadc1023292/: accessed September 24, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.