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Electron Cloud Studies for Tevatron and Main Injector

Electron Cloud Studies for Tevatron and Main Injector. Xiaolong Zhang AD/Tevatron. In This Report …. What’s Electron Cloud and it’s Effects; The impact on Main Injector Upgrades and the research activities at Accelerator Division; Simulation methods, programs and results;

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Electron Cloud Studies for Tevatron and Main Injector

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  1. Electron Cloud Studies for Tevatron and Main Injector Xiaolong Zhang AD/Tevatron

  2. In This Report … • What’s Electron Cloud and it’s Effects; • The impact on Main Injector Upgrades and the research activities at Accelerator Division; • Simulation methods, programs and results; • Future study plans. Xiaolong Zhang-FNAL, AD/Tevatron

  3. Mechanism of Electron Cloud Buildup • Short bunch: • Initial electron produced by photos, beam loss, ionization, etc. • Density of the electron increased by generating secondary electrons. • Exponential growth of electron density happens with appropriate beam conditions. • Electron cloud saturated by its space charge effect. Xiaolong Zhang-FNAL, AD/Tevatron

  4. Electrons Trapped in the Beam • Long bunch or coasting beam • Initial electron generated • Electrons are trapped by beam potential • Trailing edge multipacting (long bunch case) Xiaolong Zhang-FNAL, AD/Tevatron

  5. Effects of Electron Cloud • Vacuum instabilities: • Fast vacuum jumps of several order of magnitude • Beam instabilities • Beam losses • Heat loading • Noise on beam instruments Xiaolong Zhang-FNAL, AD/Tevatron

  6. History of Electron Cloud Studies • 1967 Novosibirk proton rings with coasting beam: • Two Stream Beam Instabilities; • Cure: various beam intensity and clearing electrode • 1970 CERN ISR coasting beam • Cure: clearing electrode • 1977 ISR bunched beam. • Vacuum pressure jumps • End of 80s: • KEK PF Beam instabilities when switched from electron to positron • PSR Beam instabilities • 1995 Two B-Factories: • KEKB: Simulation code PEI; Beam studies KEK-BEPC; • PEPII: Simulation code POSINST; LBNL-SLAC; TiN coating • 1997 ECLOUD for LHC and SPS. • CESR, APS, SNS, RHIC, etc. • New simulation codes and methods keep appearing. • Extensive SEY measurements; material and surface treatments. Xiaolong Zhang-FNAL, AD/Tevatron

  7. Electron Cloud for Various Accelerators MI Xiaolong Zhang-FNAL, AD/Tevatron

  8. Effects of the Electron CloudBeam Instabilities KEKB Sideband Peak Height BEPC PSR, 1988 Betatron Oscillation Sidebands Xiaolong Zhang-FNAL, AD/Tevatron

  9. Effects of the Electron CloudBeam Emittance Growth SPS KEKB Xiaolong Zhang-FNAL, AD/Tevatron

  10. no field dipole field Effects of the Electron CloudVacuum Pressure Bump RHIC SPS Xiaolong Zhang-FNAL, AD/Tevatron

  11. Effects of the Electron CloudNoise on BPM Pickup SPS Xiaolong Zhang-FNAL, AD/Tevatron

  12. Effects of the Electron CloudBeam Loss RHIC SPS Xiaolong Zhang-FNAL, AD/Tevatron

  13. Effects of the Electron CloudEstimation of the Heat Load for LHC (Frank Zimmermann) arc heat load vs. intensity, 25 ns spacing, ‘best’ model R=0.5 ECLOUD simulation dmax=1.7 dmax=1.5 BS cooling capacity injection low luminosity dmax=1.3 high luminosity dmax=1.1 dmax=1.3-1.4 suffices calculation for 1 train Xiaolong Zhang-FNAL, AD/Tevatron

  14. Mitigations (1) • Beam Scrubbing Xiaolong Zhang-FNAL, AD/Tevatron

  15. Mitigations (2) • Bunched Beam Injection Pattern • Solenoid Xiaolong Zhang-FNAL, AD/Tevatron

  16. Special surface profile design, Cu OFHC. EDM wire cutting. Groove: 0.8mm depth, 0.35mm step, 0.05mm thickness. Measured SEY reduction < 0.8. More reduction depending geometry. Mitigations (3) • Surface Coating with TiN or TiZrV (NEG) • Surface Grooving 1 mm Xiaolong Zhang-FNAL, AD/Tevatron

  17. E Feedthrough Mitigations (4) • Clearing Electrode E Xiaolong Zhang-FNAL, AD/Tevatron

  18. Simulations • Small section of the beam pipe. • Macro particles and discrete beam kick • Space charge, electron and beam image charge included. • Gaussian bunches (longitudinal bunch profile available for long bunches) • Realistic secondary electron yield model. • Electron longitudinal motion neglected • Theoretical primary electron distributions Xiaolong Zhang-FNAL, AD/Tevatron

  19. Secondary Electron Yield SLAC CERN Xiaolong Zhang-FNAL, AD/Tevatron

  20. Activities at Accelerator Division • Initial observation of pressure rise at Tevatron with high intensity uncoalesced beam in Dec. 2002. • Initiated by Weiren Chou and Francois Ostiguy for Proton Driver Study in April 2005. • More beam studies at Tevatron and some observations at Main Injector • Obtained simulation codes POSINST, ECLOUD, PEI, etc. • Collaborations with LBNL, CERN, APS, BNL, SLAC, etc. • Got 2 RFA electron detector as gifts from APS Xiaolong Zhang-FNAL, AD/Tevatron

  21. RFA Testing Beam Pipe in Tevatron and MI RFA ION GAUGE ION PUMP Xiaolong Zhang-FNAL, AD/Tevatron

  22. Beam Studies at Tevatron (1) Bunch intensity threshold around 4e10/bunch for 30 bunches, vacuum worsen @warm section A0, D0, C0, E0, not @B0 and F0 Xiaolong Zhang-FNAL, AD/Tevatron

  23. Beam lifetime 24.4hrs Emittance growth 34.8/hr Beam Studies at Tevatron (2) Tevatron 150GeV, 116e10/30bunches Xiaolong Zhang-FNAL, AD/Tevatron

  24. Beam Studies at Tevatron (3) Some beam Schottky power rise observed when the vacuum pressure rising Xiaolong Zhang-FNAL, AD/Tevatron

  25. Simulations for MI Upgrades • Basic beam parameters Xiaolong Zhang-FNAL, AD/Tevatron

  26. Elliptical Beam Pipe • Gröbner multipacting parameter Horz 1.28 Vert: 8.04 @30e10/bunch • Energy required for electrons to traverse beam chamber in one RF period Horz: 120 eV Vert: 19 eV • Electron energy gain at the extremities of the ellipse (impulse aproximation) Horz: 2.3 eV Vert: 7.3 KeV • Maximum beam kick (finite bunch length) 772 eV Larmor radius:0.47 mm @ 2 KGs (From Miguel Furman) Xiaolong Zhang-FNAL, AD/Tevatron

  27. Elliptical Beam Pipe With normal MI elliptical vacuum chamber and within bend magnets, at proton bunch intensity of 6e10, the electron cloud threshold for the bunch length of 0.54m, which means electron cloud happens during ramping and transition crossing where bunch length becomes shorter Xiaolong Zhang-FNAL, AD/Tevatron

  28. Elliptical Beam PipeWith Clearing Electrode Above electron cloud can be suppressed by the 500V clearing electrode in the beam pipe. Xiaolong Zhang-FNAL, AD/Tevatron

  29. 6” Beam Pipe For the 6” beam pipe, the electron cloud happens even at bunch intensity of 10e10 proton/bunch at low SEY=1.3 The electron cloud can be suppressed by 50Gs solenoid or over 500V clearing electrode Xiaolong Zhang-FNAL, AD/Tevatron

  30. Future Plan • Continue the detailed simulation for various beam and surface conditions • Beam studies at Tevatron and MI: • Electron density vs. beam intensity. • Electron energy spectrum. • Bunch by bunch tunes, loss, emittances. • Vacuum changes. • Comparing and benchmarking the simulation codes • Test of mitigation methods with the test beam pipe: Solenoid, clearing electrodes, coating, grooving, etc. • Does it exists in Booster? Xiaolong Zhang-FNAL, AD/Tevatron

  31. Summary • Electron cloud effect is a limiting factor to the high energy, high intensity accelerator performance. • It might have some impacts on magnet design. • The simulations and initial observations show the electron cloud will be a problem for SNuMi and future Fermi neutrino programs. • More studies and investments should be put into this researches. Xiaolong Zhang-FNAL, AD/Tevatron

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