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Electron cloud in the PEPII LER

M. Pivi. PEP-II - electron cloud studies – Oct 2003. Electron cloud in the PEPII LER simulations and R&D plans for higher beam intensity Mauro Pivi NLC Division SLAC. Oct 2003. M. Pivi.

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Electron cloud in the PEPII LER

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  1. M. Pivi PEP-II - electron cloud studies – Oct 2003 Electron cloud in the PEPII LER simulations and R&D plans for higher beam intensity Mauro Pivi NLC Division SLAC Oct 2003

  2. M. Pivi PEP-II - electron cloud studies – Oct 2003 Electron cloud in the PEP-II LER • At the end of last run, when horizontal tunes close to ½ integers no obvious sign of electron-cloud effect in the by-3 RF buckets spacing with minitrains + minigaps. In the by-2 configuration pattern no obvious signs of electron-cloud, but the beam current was too low to draw conclusions. • electron-cloud gradually decreased during last years due to slow conditioning of the surface. (LHC is relying on that) • When solenoid windings are turned OFF vacuum pressure rises in some locations. • electron-cloud is beam intensity dependent effect. In future upgrade of the LER at higher intensity, 3.6A, electron-cloud may re-appear – starting simulations. • Do we have enough diagnostic to tell whether and where there are electrons in the LER ?

  3. Winding solenoid field in the LER: resonances M. Pivi PEP-II - electron cloud studies – Oct 2003 e- density at by-2 and 4 RF buckets spacing, A. Novokhatski J. Seeman (PAC03 paper) Resonance multipacting in solenoid field when the electron time of flight is equal to the bunch spacing e- density at by-2 RF buckets spacing, Y. Cai and M. P. (PAC03 paper)

  4. Winding solenoid field in the LER: optimization to avoid resonances M. Pivi PEP-II - electron cloud studies – Oct 2003 e- density at by-3 RF buckets spacing, Y. Cai and M. P. (PAC03 paper). Vertical wake at by-3 RF buckets spacing, Y. Cai and M. P. (PAC03 paper). Simulation params: by-3 RF buckets spacing, bunch population 1011, drift straight section4.5 cm round vacuum chamber, stainless steel with (high) secondary yield dmax=2.0 A bit of extreme case with high beam intensity and high secondary electron yield (SEY)

  5. M. Pivi PEP-II - electron cloud studies – Oct 2003 Electron trapping mechanism in quadrupole Particular attention at quadrupoles where electron trapping mechanism is possible (magnetic mirror, see also Jackson .. !) (ex: NLC MDR quad) PEP-II arc simulations + skew quadrupole. Decay time after long gap. By-2 bucket spacing, 10 out of 12 bunches with mini-gaps, 1011 ppb. Arc quadrupole gradient 4.5 T/m and skew quarupole 2.5 T/m. Elliptic vacuum chamber 4.5 x 2.5 cm with antechamber.

  6. M. Pivi PEP-II - electron cloud studies – Oct 2003 Electron trapping mechanism in quadrupole: PSR Schematic of the Electron Diagnostic (RFA) in a PSR Quad Project in collaboration with NLC and PSR LANL

  7. M. Pivi PEP-II - electron cloud studies – Oct 2003 Future plans • install electron detectors in LER straight sections to optimize the field of the solenoid windings • Estimate of the electron trapping mechanism ongoing studies in collaboration with Los Alamos, dedicated quadrupoles in the Proton Storage Ring PSR (PEPII LER skew quadrupoles may have room to arrange electron detectors but weak field) • measurements of the secondary electron yield (SEY) and treatments of various materials at SLAC: TiN and TiZrV NEG need activation • Future simulations or full arc cell and straight section cell • More e-cloud generation simulations for PEPII (by-2, dust events..) • Need to update simulations of effects (Yunhai Cai code; QuickPIC; Headtail) • R. Kirby, F. Le Pimpec, R. Macek, T. Raubenheimer, U. Wienands, A. Wolski

  8. Winding solenoid field in the LER: resonances appear at high beam intensity M. Pivi PEP-II - electron cloud studies – Oct 2003 e- density at by-3 RF buckets spacing, resonance peaks appears at high beam intensity. Note: the energy gain of an electron sitting near the vacuum chamber wall scales as the square of the beam intensity

  9. PEP-II … values open to discussion … scale 1 to 3

  10. M. Pivi PEP-II - electron cloud studies – Oct 2003 Electron trapping mechanism in quadrupole Particular attention at quadrupoles where electron trapping mechanism is possible (magnetic mirror, see also Jackson) PEP-II skew quadrupole. Decay time after long gap. By-2 bucket spacing, 10 out of 12 bunches with mini-gaps, 1011 ppb. Arc quadrupole gradient 4.5 T/m and skew quarupole 2.5 T/m. Elliptic vacuum chamber 4.5 x 2.5 cm with antechamber

  11. M. Pivi PEP-II - electron cloud studies – Oct 2003 Electron trapping mechanism in quadrupole: PSR Project in collaboration with NLC and PSR LANL

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