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Summary of Session E: Electron Cloud an Ion Desorption A. Kraemer and S.Y. Zhang

Summary of Session E: Electron Cloud an Ion Desorption A. Kraemer and S.Y. Zhang. Three Workshops in one year: Beam Induced Pressure Rise in Rings, BNL, Dec. 9-12. 2003 ECLOUD´04, Napa, California, April 19-23. 2004 HB-2004, Bensheim, Oct. 18-22. 2004 Major Issues of Pressure Rise Workshop

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Summary of Session E: Electron Cloud an Ion Desorption A. Kraemer and S.Y. Zhang

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  1. Summary of Session E: Electron Cloud an Ion DesorptionA. Kraemer and S.Y. Zhang Three Workshops in one year: • Beam Induced Pressure Rise in Rings, BNL, Dec. 9-12. 2003 • ECLOUD´04, Napa, California, April 19-23. 2004 • HB-2004, Bensheim, Oct. 18-22. 2004 Major Issues of Pressure Rise Workshop • Ion desorption: Intensity limit of low energy heavy ion accelerators, possibly relevant for high energy hadron accelerators • Surface treatment for electron cloud and for electron and ion desorption induced pressure rise. NEG and TiN coatings. • Electron cloud for short and long bunches. EC induced pressure rise.

  2. Major Issues of ECLOUD`04 • Summary of Pressure Rise Workshop • Simulations of EC for short and long bunches. Electrons below 10eV, Quadrupole effect, simulation of heat load. • EC related beam instability and emittance growth • Supress the EC effect: solenoid fields in lepton machines, beam scrubbing at SPS and RHIC. Why the scrubbing is less effective at cold? Surface of NEG and TiN coatings. Grooved surface for beam tests. • Some Issues in HB-2004 • Summary of ECLOUD`04 • Progress in cold scrubbing at SPS, for LHC • Progress in ion beam induced desorption and others for GSI upgrade • Progress in ion beam induced desorption on cold walls for LHC heavy ion beam • RHIC pressure rise and electron cloud • Heavy ion fusion studies • Progress in code development

  3. Summary of ECLOUD`04 WorkshopRobert Macek, LANL • Progress in Cures • Weak solenoids were very effective in reducing e-cloud and ECI at B-factories (KEKB and PEP-II) • Tests of NEG coatings for reducing SEY are very encouraging (e.g. see talk by A. Rossi, also M. Pivi summary of session C) • NEG coatings planned for warm sections of LHC • Test of grooved metal surface showed 30% reduction in effective SEY (see talk by G. Stupakov) • Beam scrubbing/conditioning to reduce SEY shown to be effective for LHC beams at SPS, also effective at PSR • Tests at CERN SPS also suggest scrubbing maybe slower on a cold surface • Damping of ECI by feedback effective at SPS for coupled-bunch instabilities in the horizontal plane (see talk by G. Arduini) • Landau damping of e-p by increasing tune spread in various ways effective at PSR as is coupled Landau damping

  4. Electron clouds and pressure rise in RHICW. Fischer, BNL Pressure rise mechanisms considered so far • Electron cloud  probably dominating for operational problems • Coherent tune shift in bunch train • Electron detectors • Comparison with simulations • Ion desorption  tolerable for operation • Rest gas ionization, acceleration through beam • Ion energies ~15 eV for Au, ~60 eV for p • Visible pressure rise, may lead to instability in conjunction with electron clouds (Au only) • Beam loss induced desorption tolerable for operation • Need large beam loss for significant pressure rise • New desorption measurements in 2004 (H. Huang, S.Y. Zhang, U. Iriso, and others)

  5. Measurements on Beam Induced Desorption at GSIH. Kollmus, GSI September 2004: First test-experiment to measure ion beam induced desorption yields of U73+ at energies from 15 to 1000 MeV/u bombarding stainless steel 316LN, stainless steel P506, Al, Cu and Inconel625 Experiment by: M.C. Bellachioma, M. Bender, H. Kollmus, A. Krämer (GSI), E. Mahner (CERN), O. Malyshev (ASTeC; UK), L. Westerberg, E. Hedlund (TSL; Sweden) Results: • preliminary energy dependence for U73+ measured – dE/dx scaling Todo: • charge state dependency? • angle dependency of desorption yield – depth of energy loss test of dE/dx • desorption yields of cold surfaces (with condensed gases) • ERDA-Measurements – understanding of the physics behind the ion induced desorption

  6. Dipole field (30-50 K), 25ns bunch spacing 3.7 W/m 0.35 W/m LHC extrapolation (calculation) LHC and SPS electron cloud studiesJ.M. Jimenez, CERN Physisorbed water identified as a potential problem: • Conditioning has been observed in the SPS if the cold detector is protected against water back streaming from the unbaked parts • In the LHC, low water coverage is expected: • Pumping down to 10-4 torr of the cold parts prior to the cooling • Controlled cool down sequence where the cold bore is cooled while the beam screen is kept as warm as possible

  7. Ion Desorption Issues at RHICS.Y. Zhang , BNL • Ion Desorption and RHIC concerns • Normal incident, yield 1 to 10. Scraping incident, yield 105 observed at low energy heavy ion accelerators • Ion desorption may cause pressure rise at RHIC. More concerned is the positive ion production, which may explain the electron multipacting in RHIC warm sections, with large bunch spacing. • RHIC observations and studies • Many cases show large desorption rate, but the contributions of electron multipacting or non-beam ions are not clear. • Cases of collimator scraper and other indicate desorption rate 107 or higher. • Similar desorption rate in beam studies, but only in irregular cases. More beam study is needed.

  8. A new cold-bore experiment for heavy-ion induced desorption studies at low temperatures: first results obtained at 300K, 77K, and 15KE. Mahner, CERN Motivation: Electron Capture by Pair Production • New cold-bore setup for heavy-ion induced • molecular desorption experiments, in collaboration • with GSI, at LINAC 3. • Pb53+ ions (4.2 MeV/u) bombarded under grazing • incidence (14 mrad) onto Cu. • Desorption studied with single shots and scrubbing • at 300 K, 77 K, and 15 K. • Partial and total pressure rise measurements at all • temperatures. • Results (all preliminary) • Single shots: • Yields decrease with temperature • Scrubbing runs (short): • Smaller pressure rises at lower temperatures. • CO and H2 dominate at 300 K, H2 at 77 K and 15 K. • Very low P measured directly on the 15 K cold • Bore. John Jowett • Secondary Pb81+ beam out of IP. Energy deposition by ion flux onto a Cu beam screen in a dispersion suppressor dipole • Potential Consequences • Quench limit exceeded • Heavy-ion induced desorption of cold surfaces? Unknown!

  9. P0, t0 Pe < P0, te >t0 P > P0, t<t0 Modeling of beam loss induced vacuum breakdownE. Mustafin, GSI • The use of the diffusion type equation to simulate the vacuum pressure evolution has been proven to be a fruitful approach in theoretical consideration of the vacuum breakdown description in the heavy-ion machines. • The proposed method allows to describe the vacuum instability development, steady-state vacuum pressure profiles and the other phenomena related to the beam-loss induced pressure rise. • Further work is necessary to determine experimentally the phenomenological parameters of the theory RHIC GSI SIS18 U28+ at constant energy

  10. 409220100 - 409220138 Intense Ion Beam transport in Magnetic Quadrupoles: Experiments on Electron and Gas Effects, P. A. Seidl (LBNL) Electron physics & beam dynamics Rough surface reduces desorption, e- coefficient (from primary ion). 2nd generation electron cloud diagnostics deployed. Testing a self-consistent model of e-, K+ in magnetic quadrupoles; vs experiment with large source of e- Experiment: clearing electrodes & e-supressor off K+, e- dist. In quadrupole. 3D PIC simulation with e- e- (color) 2 < t < 3 s 3 s Y X' K+ (black) magnet bore X X X 1 MeV, 0.18 A, t ≈ 5 s, 6x1012 K+/pulse, beam potential ~2 kV

  11. The CMEE library for computer modeling of ion-material interactionsP. Stoltz, presented by D. Bruhwiler, Tech-X Corp. • CMEE = Computational Modules of Electron Effects • • Latest version of CMEE now provides routines for modeling • – secondary electron yield • – Ion stopping, range, and ion-induced electron yield • – neutral gas ionization by electrons and protons • • The approach is • – use tested routines • – make them available on any platform or language • CMEE secondary electron model based on POSINST routines • CMEE ion-material routines are based on CRANGE code • CMEE impact ionization routines are based on fits from Reiser • The next release of CMEE will include some heavy-ion cross sections (ionization, stripping, capture, excitation) • The next release of CMEE will also include ion scattering

  12. Estimations of beam life time in the SIS18G. Rumolo, GSI Losses for U28+, U73+ and Ar10+ over acceleration ramp • Projectile and target ionization can both be responsible for beam loss in the SIS18. • Beam losses from few tenths of percent to about 20% (U28+) can be expected to occur during the ramp, even if the ring operates in a stable regime. • More accurate information on the energy and angle dependence of the desorption yield is necessary for the prediction of a safe region of operation for the SIS18 under tolarable losses. Initial currents (N0) were chosen between 0.1 and 0.9 Nthr . Currents very close to the threshold value can lose up to almost 20% over the ramp. For U73+ and for Ar10+ (currents N0= 0.9 Nthr), losses are much smaller over the ramping time.

  13. Test of Anti-grazing Ridges at RHICS.Y. Zhang and P. Thieberger, BNL IV. Summary and remarks 1. RHIC warm EC • RHIC warm section electron cloud is currently a luminosity limit. • It is not a normal electron cloud, beam halo scraping may have played a role in electron's lifetime. 2. Ion desorption in scrapings • A new model of ion desorption with scraping angles is proposed. • Anti-grazing ridges have been installed to study the effect on RHIC warm electron cloud. 3. An addition to surface cures • For normal incident, rough surface reduces secondary electron yield. • Grooved surface may reduce SEY, with similar mechanism. • RHIC anti-grazing ridge is designed to reduce beam scraping generated ions.

  14. Working Session Discussion I • E-Cloud Issues • • Missing physics for hadron machines: • • Contributions from residual gas at PSR is significantly larger than from simulations. • • Electrons (sometimes) survive long time, observed at SPS (for fixed target after LHC beam) and RHIC warm straight sections. Are ions playing a role? • • Quadrupole effect • • SPS observed strong electron multipacting at quadrupole in a pattern predicted by simulation. • • Effect of electrons below 10eV • 2. Ion Desorption • • GSI, CERN, BNL test stands • • RHIC concerns and studies • • Among many aspects, incident angle effect • • RHIC study showed that mrad, no dramatic increase of desorption rate. Even smaller angle? • • GSI plans test of angular effect. • • Ions from other sources, ionization, low energy electrons

  15. Working Session Discussion II 3. Cryogenic Problem • SPS COLDEX and cold scrubbing • Scrubbing inefficiency at cold walls is identified due to water, opened door to LHC scrubbing • Some discrepancies between electron signal and heat load. • RHIC cold pressure study • Cold pressure rise observed at 2x1011 protons/bunch with 108ns bunch spacing. Study is prepared. • eRHIC, with 1011 charges/bunch, 35ns bunch spacing will have same problem as LHC. 4. Surface • NEG, large scale installation at RHIC • Activation reactivation, saturation, and possible poissoning. • RHIC activate at 250°C, 1hour per CERN´s recipe; but CERN is doing 230°C, 24hours • TiN • Serrated and grooved surfaces • Anti-grazing ridges

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