NLC Synchrotron Radiation and Beam Pipe Radius

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NLC Synchrotron Radiation and Beam Pipe Radius

• Stan Hertzbach
• UMass
• Snowmass 2001
• 5 July 2001

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SR Calculations

• These SR calculations were for
• 500 GeV center of mass energy
• 4.3 m L
• Optics does not include sextupoles or octupoles
  which have become very important FF elements.
• Halo is assumed to be a very broad Gaussian,
  often called a flat halo.
• Ideal halo collimation assumed.

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What Limits Vertex Detector Radius?

• Radius allowed by beam-beam interaction pairs is
  determined by detector solenoid strength.
• Radius could be limited by exposure to neutrons
  from beam dump depends on dump line design.
• Radius certainly limited by synchrotron radiation
• SR from beam halo presents most strict limit
• depends on collimation
• depends somewhat on assumptions about halo
• SR from Gaussian core of beam also limits radius
• allow for larger than nominal emittance at
  startup
• allow for energy variation

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Halo SR at the Beam Pipe
Assumes 1E-3 halo Eg 3-4 MeV Sextupoles not yet
included Effective vs. Ideal accounts for 1 beam
energy spread and planar collimation
Flare
Min. radius
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Halo Synchrotron Radiation Fans with 240 mrad x
1000 mrad Collimation
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Beam Pipe Radius Limit from Larger than Nominal
Emittance

• Larger than nominal emittance Gaussian beam.
• Startup issues.
• Factor of 2 in beam size is factor of 4 in
  emittance.
• Running below nominal energy (500 GeV Ecm) will
  mean reduced luminosity and/or larger emitttance.
• SR Hit Density (hits/mm2) on Inner Wall of Beam
  Pipe

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Beam Pipe Radius Limit from Energy Tails

• If radius is very small, synchrotron radiation
  from the core Gaussian beam sets the limit.
• Vertex detector hit density hit density on beam
  pipe.
• SR Hit Density (hits/mm2) on Inner Wall of Beam
  Pipe
• for 3 collimation depths and as beam energy varies

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Work in Progress

• Sextupoles and octupoles must be included.
• Rather than add sextupoles and octupoles to the
  synchrotron radiation code, the code will be
  interfaced with standard optics codes, starting
  with DIMAD.
• The code has been reorganized for this purpose,
  and new algorithms have been checked.
• SR calculations just need the particle trajectory
  into out of each element.
• Currently interfacing with DIMAD, thanks to PT.
• Had hoped to have first results here, but ...