ILCDR08 Report Electron Cloud Session

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ILCDR08 Report- Electron Cloud Session -

• 2008.07.08 11 _at_Cornell Univ.

Y. Suetsugu, KEK
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Electron Cloud Group Charge(M. Palmer)
The charge to the Electron Cloud working group is
to review the status of electron cloud
simulations, both for electron cloud growth and
for electron cloud induced beam dynamics, the
benchmarking of the major codes against each
other, and benchmarking of the codes against
experiment. The group should also review the
status of electron cloud measurement and
mitigation techniques. Finally, the group should
look at the world-wide experimental program and
inputs that are required for the ILC and CLIC
damping ring designs, paying particular attention
to identifying tests that are needed as part of
the CesrTA program. ______________________________
____________________ This charge is quite
ambitious we made headway, but continuing
discussions and real work will be required to
fulfill the charge
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Four Working Groups

• Measurements
• Electron cloud build up, effect on beam
• Simulations
• Benchmarking, build up, effect on beam
• Mitigation techniques
• Coating, groove, clearing electrode
• Experimental plans
• Each Lab., CESR TA

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Talks in Measurement WG

• Cloud Build up
• K. Kanazawa (KEK), R. Zwaska (Fermi Lab.) and S.
  Greenwald (Cornell) RFA Retarding Field
  Analyzer monitors
• S. De Santis (LBNL) Microwave transmission
• Effects on Beam
• K. Ohmi (KEK) Incoherent emittance growth
• J. Flanagan (KEK) Coherent instability
• R. Holtszpple (Alfred Univ.) Tune shift using
  witness bunch

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Measurement (Kanazawa)

• RFA type electron detectors with Faraday cup or
  MCP or multi-strip anode are installed to KEKB
  LER.

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Measurement (Greenwald)

• Comparison between Cornell-type thin RFA and
  APS-type
• Almost consistent each other
• Newly developed RFA for
• CESR-TA
• Dipole Chamber RFA

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Measurement (Santis)

• Electron density can be estimated by measuring
  the phase shift of transmitting microwave

• Instruments were set up
• for CESR-TA, following PEP-II

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Effects on Beam (Flanagan)

• Head-tail instability Synchro-Betatron sidebands
• The behavior is consistent
• with simulation

J. Flanagan, ECLOUD07
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Effects on Beam (Holtzappie)

• Tune shift measurement using witness bunch
• Use long trains e/e- bunches to generate a
  electron cloud density.
• Place witness bunches
• at varying times after
• the generating train
• and measure the
• coherent tune shift
• of the witness bunch.

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Summary

• Build up
• Thin RFA is prepared for wiggler section
  (B-magnet)
• Microwave transmitting method with better
  hardware
• Measurement in Q-magnet or in solenoid field
  Future issues
• Effect on beam
• Measurement of coherent instabilities, incoherent
  emittance growth
• Tune shift
• Beam size Development of X-ray beam size monitor
• Provide valuable data for verification of
  simulation codes.

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Talks in Simulation WG
(M. Furman)

• G. Dugan Simulations at Cornell for CesrTA
• J. Calvey Simulations for RFA studies at
  CesrTA
• J. Crittenden Simulations for witness bunch
  studies at CesrTA
• T. Demma Build-up of electron cloud in DAFNE
  in the presence of a solenoid field
• C. Celata Electron cloud cyclotron resonances
  for short bunches in magnetic fields
• K. Ohmi Study of electron cloud instabilities
  in CesrTA and KEKB
• All but the last talk are about build-up ecloud
  physics

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What is to be done (1)
(M. Furman)

• Understand e-cloud build-up, decay, and
  spatial/energy distribution
• Benchmarking of build-up codes
• Bring the codes (ECLOUD, CLOUDLAND, POSINST)
  into agreement
• Rediffused electrons likely to be the source
  of the discrepancy
• Simulate a few beam fill patterns
• Obtain electron flux Je and dN/dE at RFAs
• Obtain transverse distribution of e-cloud at
  dipoles
• Fit basic SEY parameters to the above so as to
  agree with data
• Predict Je, dN/dE, tune shift along train and
  transverse electron distribution for other fill
  patterns
• This subprogram will
• Characterize the e-cloud distribution around the
  machine
• Increase the confidence in build-up codes

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What is to be done (2)
(M. Furman)

• Understand effects of the e-cloud on the beam
• Available codes HEADTAIL, WARP, PEHTS, CMAD,
• CesrTA e-cloud RD is driven by the necessity to
  preserve a very low beam emittance. This will
  bring intense scrutiny of e-cloud codes that
  compute effects on the beam
• To a large degree, this subprogram can proceed in
  parallel with the build-up subprogram
• Just assume a value for the e-cloud density near
  the beam and proceed
• Look at single bunch (coherent and incoherent)
  effects
• Multi-bunch coherent effects
• As the build-up subprogram provides more
  information on the e-cloud around the ring,
  refine the understanding of the e-cloud effects
  on the beam

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Talks in Mitigation WG

• F. Caspers (CERN) Microwave transmission
  recent measurements in the SPS and LHC ?
  Measurements?
• M. Pivi (SLAC) Mitigations experiments at SLAC
• R. Zwaska (Fermilab) Plans for a resistive
  electrode
• Y. Suetsugu (KEK) Experiment on clearing
  electrode at KEKB positron ring
• M. Palmer Mitigation studies presently included
  in the CesrTA program

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ECLOUD2 Grooved Chambers Performance M. Pivi
M. Pivi et al, SLAC
Electron cloud signal in two smooth (flat)
TiN-chambers and two grooved
TiN-chambers installed in PEP-II.
Electron cloud signal in stainless steel chamber.
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Conditioning surfaces in PEP-II M. Pivi, SLAC
(M. Pivi)

• Stability of TiN coating

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Clearing Electrodes in KEKB Y. Suetsugu, KEK
(M. Pivi)
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Mitigation tests in Cesr TA M. Palmer, Cornell
(M. Pivi)
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Recommendation for mitigation as input for DR
design Discussion All
(M. Pivi)
Preliminary table to be completed as input for
Technical Design Phase. Goal is to turn all Red
colors to Green in the next two years. Other
mitigations under development! (ex Carbon
coating CERN)
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Summary
(M. Pivi)

• Successful RD program on electron cloud
  mitigations.
• TiN coating has been demonstrated to have an SEY
  below the instability threshold. Work continues
  to address a few remaining issues.
• Yet, requirements at future colliders (2
  picometer emittance in the ILC DR, e.g.) are
  challenging.
• Hence, close collaboration between labs to
  develop complementary mitigation techniques is
  needed to further suppress the electron cloud
  effect.

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Talks in Experimental Plan WG
(G. Dugan)

• G. Dugan (Cornell) Cesr-TA experimental plans
• Y. Suetsugu (KEK) Experimental Plan at KEKB
  Positron RingGrooved Surface, and Clearing
  Electrode Ver.2
• K. Kanazawa (KEK) Plan of measuring cloud
  density in the solenoid field and in the
  quadrupole field
• W. Fischer (BNL) EC plans in connection with
  eRHIC
• General discussion on key experiments for
  experimental planning-focused on code validation
  and mitigation techniques-all

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CESR EC experimental areas

• L3 Straight Experimental area
• Instrument large bore quadrupoles and adjacent
  drifts
• Install of PEP-II experimental hardware
  (including chicane) in early 2009
• Provide location for installation of test chambers

(G. Dugan)

• Arc experimental areas
• Instrument dipoles and adjacent drifts
• Provide locations for installation of test
  chambers, in drifts where wigglers were removed.

• L0 Wiggler Experimental area
• All wigglers in zero dispersion regions for low
  emittance
• Instrumented wiggler straight and adjacent
  sections

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Experimental Setup
Y. Suetsugu, H. Fukuma, KEK M. Pivi and W. Lanfa,
SLAC
Experimental Plan at KEKB Positron RingGrooved
Surface, and Clearing Electrode Ver.2
(G. Dugan)

• Use the same location

Wiggler magnets B 0.75 T
Groove
R47
Magnetic field
Beam
Monitor
Test chamber with antechambers
Gate Valve
Gate Valve
Beam
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Plan of measuring cloud density in the solenoid
field and in the quadrupole field
(G. Dugan)
K. Kanazawa (KEK)
QUADRUPOLE

• SOLENOID
• Given a solenoid field and the position of
  detection, the energy of measured electrons is
  automatically selected (the volume is
  automatically defined).

Electrons accelerated by a bunch along X-axis
reach the detector.
X-axis
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Key questions for experimental planning
(G. Dugan)

• Cloud build up
• -What experiments will best pin down the SEY
  model parameters, particularly the number of
  rediffused electrons? The photoelectron
  generation model parameters?
• Fit of cloud saturation as measured by RFA to SEY
  peak and SEY yield at zero energy.
• Fit RFA energy-differential current and/or tune
  shift as a function of beam current and time to
  disentangle photoelectron parameters from SEY
  yield parameters. Transverse shape of RFA current
  measurement can be sensitive to SEY model
  parameters.
• RFA measurements in quadrupole can be important
  since they are at peak beta values.
• Improved RFA time resolution is important.
• TE wave transmission can measure growth and decay
  of average cloud density in a local area of the
  ring.

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Key questions for experimental planning
(G. Dugan)

• Effect on beam
• -How can we test that the effects of the pinch
  are being properly modeled?
• Head-tail instability threshold.
• Bunch length dependence of tune shift
  measurements
• -How can we best establish confidence in the
  instability predictions? The predictions for
  emittance growth?
• Scaling-Threshold of head-tail instability-depende
  nce on beam size? Dependence is stronger on sync
  tune, avg beta, chromaticity. Should be roughly
  independent of emittance.
• Emittance growth-need transverse feedback, turn
  by turn beam size measurements. Difficult
  measurement. Codes that can be validated here
  WARP, Ohmis PEHTS, HEADTAIL

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Key questions for experimental planning
(G. Dugan)

• Other bench measurements (e.g. SEY secondary
  spectrum) which could help establish code
  parameters?
• Measure (using Auger spectrometer) secondary
  spectrum of initial (and irradiated?) chamber
  samples.
• Measure lt15 eV part of SEY curve-light sources?
  Try to think of other ways to do this.
• XPS to measure photoelectron spectrum (or with
  synchrotron light beam line from CHESS?) and
  photon reflectivity vs. energy, angledata may
  exist for the latter.

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Key questions for experimental planning
(G. Dugan)

• Mitigation Techniques
• -What additional experiments are needed to
  establish high confidence in the proposed
  mitigation techniques to be used in the ILC
  damping ring?
• Repeat measurement of EC cloud suppression for
  TiN and NEG.
• Investigate chamber exposure to gases such as
  SF6, N2, O2.
• Try carbon coating proposed for SPS-durability
  under SR radiation
• Long term lifetime of TiN-PEP II and KEK can
  provide data.
• Clearing electrodes in wiggler and dipole, and
  grooves in dipole. Grooves for wiggler chamber
  should continue to be studied.
• Investigate feasibility of measuring transverse
  wake from single grooved chamber (and electrodes)
  using local field probes.

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Summary
(M. Furman)

• Cesr TA A superb and ambitious e-cloud RD
  program
• Essential resources are in place
• Hardware
• Diagnostics and simulation tools
• Operational expertise
• Knowledge, flexibility and maturity of the
  machine
• e / e, almost arbitrary fill pattern,
• Knowledge of certain relevant e-cloud parameters
• Dedicated beam time
• Close collaboration with outside experts is
  highly desirable to make rapid and sustained
  progress
• I have a suspicion that 2 years will not be
  enough to achieve all the desired goals
• Nevertheless, I am quite confident of a large
  degree of success, both for Cesr TA in
  particular, and for the e-cloud field in general.

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Comments from the CesrTA PM

• Working Group Summaries
• Electron Cloud
• CesrTA offers a unique opportunity to benchmark
  simulation codes over a wide range of parameters
  and to study both EC growth and beam dynamics
  issues that are critical for damping ring
  performance
• Very promising recent results on mitigation
  techniques
• Much remains to be done to ensure a viable (and
  economical) solution for the damping rings
• Mitigation techniques and ring design must be
  integrated into an overall design
• Significant questions remain on surface physics
  issues
• CesrTA offers a chance flexibly explore the
  integrated effect
• Collaboration support for further surface science
  studies could be very beneficial
• CesrTA program will aggressively pursue a broad
  range of experiments to characterize the EC
  parameters that are necessary to provide
  confidence in the damping ring design