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Electron-Cloud Activities at PSR R. Macek, 8/8/05

Electron-Cloud Activities at PSR R. 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

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Electron-Cloud Activities at PSR R. Macek, 8/8/05

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  1. 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 RJM_E-cloud Diag.ppt

  2. 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) RJM_E-cloud Diag.ppt

  3. Layout of proposed electron sweeping detector for quads RJM_E-cloud Diag.ppt

  4. Hole pattern at entrance to RFA RJM_E-cloud Diag.ppt

  5. 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 RJM_E-cloud Diag.ppt

  6. Simulation results (trapping etc) RJM_E-cloud Diag.ppt

  7. 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 RJM_E-cloud Diag.ppt

  8. Another view of ExB drift RJM_E-cloud Diag.ppt

  9. 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 RJM_E-cloud Diag.ppt

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