ElectronCloud Activities at PSR R' Macek, 8805

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Electron-Cloud Activities at PSRR. Macek, 8/8/05

• Development of electron cloud diagnostic for
  quadrupoles
• Collaboration LANSCE, TechSource (SBIR), Pivi
  (SLAC)
• Simulations, physics design have been carried out
  
• Engineering design and fabrication to start soon
• Will give short summary of these activities
• Test of active damping of e-p instability
• Collaboration LANSCE, SNS, IU, LBNL
• Analog system for the vertical has damped the
  instability in recent tests
• To be discussed in future call
• Monitoring of e-cloud signals during routine
  operations
• See effects of beam scrubbing, effect of 3 week
  off period and more data on 1st pulse
  instability

See SBIR Phase II proposal from TechSource and
Technote by Macek and Pivi on ExB drifts in PSR
quads and dipoles
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Motivation for quad diagnostic

• Where are dominant sources of electrons driving
  the e-p instability? Drift spaces, dipoles or
  quads?
• Attempts to control the e-p instability by
  suppressing the electron cloud formation using
  clearing fields, TiN coatings and weak solenoids
  in drift spaces at PSR have been ineffective.
• Beam scrubbing on the other hand has been
  effective.
• This suggests that the dominant sources of
  electrons are not generated by beam-induced
  multipacting in drift spaces.
• Why suspect quadrupoles?
• Expect seed electrons born at the wall to be
  strongest in quads by as much as a factor of
  10-100 compared with drifts or dipoles
• Seed electrons from grazing angle beam losses are
  a strong function of angle (sin-1(?)) and
  grazing angles will be smallest in quads where
  b-functions are largest
• Losses from foil scattering largest in quads
  where b-functions are largest
• Expect electrons surviving the gap between
  bunch passages to be most effective driving the
  instability
• Quads can trap a significant number during the
  passage of the gap
• Simulations show long lifetime after beam has
  left the quad
• Collection of electrons from biased BPM
  electrodes gave largest signal in a quadrupole
  compared with drift and dipole.
• At CERN SPS, strip detector in quadrupole gave
  larger signal than for dipole or drift

Theiberger et al, Phys Rev A, vol 61 042901
(2000)
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Layout of proposed electron sweeping detector for
quads
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Hole pattern at entrance to RFA
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Simulation of electron cloud generation in PSR
quads

• Use POSINST 12.1
• 3D quad field (graph below)
• Seed electrons from beam losses in quad (100
  e/lost proton), p loss rate 4.4x10-8/m/proton

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Simulation results (trapping etc)
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Large ExB drift

• Many electrons from quad ejected in drift during
  the presence of the beam
• Significant source of seed electrons for drifts
  adjacent to quads
• Example in the simulation
• Also agrees with analytical calculation

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Another view of ExB drift
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Status of e-sweeper for PSR quad

• Phase I SBIR complete (Physics Design)
• Phase II (2 year grant) has awarded to TechSource
• CRADA being developed with LANSCE
• Plan
• Engineering design and fabrication and
  installation in a spare PSR quad over the next
  12-13 months
• Installation of quad with detector and run beam
  tests in the following 6-7 months