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

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
• ECLOUD04, 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.

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• Major Issues of ECLOUD04
• 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 ECLOUD04
• 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 ECLOUD04 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

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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)

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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
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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

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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.

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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!
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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
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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 lt t lt 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
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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

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Estimations of beam life time in the SIS18G.
Rumolo, GSI
Losses for U28, U73 and Ar10 over acceleration
ramp
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.

• 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.

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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.
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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

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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
250C, 1hour per CERNs recipe but CERN is doing
230C, 24hours TiN Serrated and grooved
surfaces Anti-grazing ridges