Electron Cloud Update US LHC Accelerator Research Program

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Presentation transcript:

Electron Cloud Update US LHC Accelerator Research Program bnl - fnal- lbnl - slac Electron Cloud Update Miguel A. Furman (LBNL) mafurman@lbl.gov LARP Collaboration Mtg. Pheasant Run (Illinois) Oct. 5-6 2005 LARP-Pheasant Run Oct. 2005 Electron Cloud - M. Furman

Electron Cloud - M. Furman Recent activities BNL CERN e– detectors for IP12 (not LARP funded, but important) Two dipole magnets, B0.2 T, room temperature (one detector/dipole) J. Miguel Jiménez to come this month to BNL for installation Testing and calibration during 2006 run (A. Drees) Ping He now working on ecloud LBNL Summer student (V. Chaplin, July 2005) Updated simulations of ecloud power deposition for LHC arc dipoles (next viewgraph) Renewed RHIC simulations; goal: map out parameter space Calibrate against measurements Explain phase transitions Augmented diagnostic capability of POSINST code Quantify effects from various components of the electron-emission spectrum 3D self-consistent code (WARP/POSINST) Not LARP-funded in FY05 Initial results for one LHC arc FODO cell in early 2005 (LARP mtg, Apr. 05) Will take up in FY06 (Jean-Luc Vay) LARP-Pheasant Run Oct. 2005 Electron Cloud - M. Furman

Simulated LHC arc dipole power deposition bunch spacing: tb=25 ns Aver. power deposition vs. bunch intensity for a given peak value of the SEY (POSINST and ECLOUD codes) * “LTC40”: LHC Tech. Committee. Mtg #40, April 2005 (CERN simulations, presented by F. Zimmermann) LARP-Pheasant Run Oct. 2005 Electron Cloud - M. Furman

Same as previous (tb=25 ns) but no rediffused electrons(*) Motivation: POSINST model w/o rediffused ≈ ECLOUD model (*) We set dr=0 and simultaneously increased de and dts by a common factor such that dtot remained the same This is “good agreement” by the standards of the trade (IMHO) LARP-Pheasant Run Oct. 2005 Electron Cloud - M. Furman

Bunch spacing: tb=75 ns (POSINST code) LARP-Pheasant Run Oct. 2005 Electron Cloud - M. Furman

Updated LHC dipole simulations: conclusions No problem for tb=75 ns, even up to Nb=1.6x1011 and dmax=2 In qualitative agreement with CERN results If rediffused electrons ignored, good agreement with CERN simulations As expected (similarity of models) No problem up to dmax≈1.4 (for Nb=1x1011) But rediffused electrons are there Our model is based on bench measurements of emission spectrum for Cu Maximum acceptable dmax≈1.3 (for Nb=1x1011) Caveats: Power depos. estimates above are based on 1 batch (=72 bunches + gap) Steady-state estimates are higher by ~30-40% d(0) varies in 0.3-0.5 depending on dmax; we have not assessed sensitivity to d(0) separately from dmax LARP-Pheasant Run Oct. 2005 Electron Cloud - M. Furman

Goals for FY05-06 (list from LARP mtg. April 05) LHC heat-load estimate: POSINST-ECLOUD benchmarking (*) essentially done 3D beam-ecloud self-consistent simulations (*) ongoing Electrons, gas, ions, … Main goal: understand effects from ecloud on beam Analyze June 2004 SPS data (*) ongoing Especially e– energy spectrum Constrain SEY model for better predictions for LHC Benchmark CERN calculations sz dependence Help define optimal LHC conditioning scenario (*) not started Define optimal fill pattern during first two (?) years of LHC beam Apply Iriso-Peggs maps to LHC (*) not started Understand physics of map simulation technique Understand global e-cloud parameter space, phase transitions Simulate e-cloud for RHIC detectors (**) just begun Calibrate code Then predict BBB tune shift Simulate e-cloud for LHC IR4 “pilot diagnostic bench” not started What to expect when high-N, low-sb beam turns on (*) endorsed by CERN AP group (**) endorsed by CERN vacuum group LARP-Pheasant Run Oct. 2005 Electron Cloud - M. Furman

Electron Cloud - M. Furman Additional material LARP-Pheasant Run Oct. 2005 Electron Cloud - M. Furman

Calibration of POSINST at APS (e+ beam) time-averaged e– flux at wall vs. bunch spacing (Furman, Pivi, Harkay, Rosenberg, PAC01) LARP-Pheasant Run Oct. 2005 Electron Cloud - M. Furman

Calibrating POSINST at PSR bunch length ~60 m a portion the EC phase space is in resonance with the “bounce frequency” “trailing edge multipacting” (Macek; Blaskiewicz, Danilov, Alexandrov,…) (ROAB003; RPPB035) ED42Y electron detector signal 8mC/pulse beam (simulation input) 435 mA/cm2 electron signal (dmax=2.05) measured (R. Macek) simulated (M. Pivi) LARP-Pheasant Run Oct. 2005 Electron Cloud - M. Furman

Three components of secondary emission: sample spectrum at E0=300 eV from M. F. and M. Pivi, PRST-AB 5, 124404 (2002) LARP-Pheasant Run Oct. 2005 Electron Cloud - M. Furman

Electron-wall collision energy comparison w/wo rediffused electrons Four successive bunches in a 25-ns batch ~5 ns after bunch passage: 1st wave of electrons hits the wall (were kicked by the beam) ~5 ns later: second wave of electrons hits the wall; these were mostly rediffused electrons created when the 1st wave hit the wall NB: the 2nd wave is absent in the “NR” case (“no rediffused”) LARP-Pheasant Run Oct. 2005 Electron Cloud - M. Furman

Effective SEY comparison w/wo rediffused electrons The 2nd wave leads to a higher effective SEY (deff) than in the “NR” case… [definition: deff= (no. of emitted electrons)/(no. of incident electrons) averaged over all electron-wall collisions anywhere on the chamber wall, over any given time interval] LARP-Pheasant Run Oct. 2005 Electron Cloud - M. Furman

Average electron line density comparison w/wo rediffused electrons …which leads to ~twice the number of electrons… LARP-Pheasant Run Oct. 2005 Electron Cloud - M. Furman

Average power deposition comparison w/wo rediffused electrons …which, in turn, leads to ~twice the power deposition. Most of the power deposition comes from the 1st-wave electrons. The factor ~2 is mostly because there are ~twice the number of electrons. The 2nd wave contributes an additional ~5-10% of “direct” power deposition (small bump ~10 ns after the bunch passage) LARP-Pheasant Run Oct. 2005 Electron Cloud - M. Furman

The electron-cloud effect in LHC Beam synchrotron radiation is important provides source of photo-electrons Secondary emission yield (SEY) d(E) is important characterized by peak value dmax determines overall e– density e– reflectivity d(0) is important determines survival time of e– Bunch intensity Nb and beam fill pattern are important Main concern: power deposition by electrons LARP-Pheasant Run Oct. 2005 Electron Cloud - M. Furman