ElectronCloud Code Benchmarking

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Electron-Cloud Code Benchmarking Simulations

• Elena Benedetto, Daniel Schulte,
• Cristina Vaccarezza, Rainer Wanzenberg,
• Frank Zimmermann
• plus new postdoc new associate!
• main labs involved CERN, DESY, INFN

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D. Schulte, R. Wanzenberg, F. Zimmermann, ECLOUD0
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e-cloud in TESLA dogbone damping ring
e- line density
photon flux at wall
ECLOUD code
PHOTON code
le1010 m-1
wiggler
arc
straight section
central volume density
emittance growth
ECLOUD code
HEADTAIL code
re5x1012 m-3 ?above threshold
threshold of weak instability at re2x1012
m-3 with e-cloud only in the wiggler (length
C/30)
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• EUROTeV WP3 ECLOUD plan for the
• next 12 months (June 05 - June 06)
• and beyond
• international context (ILC collaboration)
• work done in the first six months

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• Plan for the next 12 months beyond
• Goal 1. Train one new postdoc and one new
  scientific associate in electron-cloud
  simulations
• Milestones
• 1.1 Spring Advertise positions at DESY CERN
• 1.2 July 05 Recruit new postdoc (DESY, start
  July 05 ) new scientific associate (CERN,
  start date 01. July 05)
• 1.3 September 05 First set of simulations from
  newly hired staff

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Goal 2. Benchmarking of the existing code for
electron- cloud build up by comparison with other
simulations experiments Milestones 2.1 May
05 Compare e-cloud build-up simulations for SPS
strip detector (flux for different batches
inter-train gaps) with experimental results 2.2
August 05 Compare predictions from e-cloud
build-up simulations for SPS COLDEX experiment
(flux heat load) with experimental
results. 2.3 December 05 (too optimistic?) -gt
June 06 Perform e-cloud build up simulations for
DAFNE wiggler qualitative comparison with
measurements (pressure, beam instability,
possibly designated electron detectors). 2.4 June
06 Study efficiency of various proposed
countermeasures in simulations 2.5 August 06
Study importance of electron build up in
damping-ring quadrupoles
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Goal 3. Benchmarking of the existing code to
simulate the e-cloud instability by comparison
with experiments, in particular in the SPS and
DAFNE Milestones 3.1 December 05 Compare
instability observations at the SPS and the
instability suppression by higher chromaticity
with simulation results 3.2 February 06 Compare
SPS experimental lifetimes with HEADTAIL
simulations of emittance growth below the fast
instability threshold 3.3 March 06 Compare
measured instability growth rates in DAFNE with
single-bunch growth rates simulated by the
HEADTAIL code and with multi-bunch growth rates
estimated from the ECLOUD build-up simulations
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Goal 4. Improvement of the simulation
codes Milestones 4.1 June 05 (problem-gtJuly
05?) Implement realistic wiggler models for
DAFNE representing the nonlinear wiggler fields
before and after pole modifications. 4.2 August
05 Implement realistic wiggler models for the
ILC damping ring and, possibly, for CLIC. 4.3
August 05 Implement the possibility of
extracting multi-bunch and coupled-bunch
head-tail wake fields from the ECLOUD code. 4.4
September 05 Improve the modeling of electron
loss for vacuum chambers in a magnetic field, so
that artificial drifts are avoided.
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Goal 4. Improvement of the simulation codes
contd Milestones contd 4.5 February 06
Implement an antechamber geometry, and, if
foreseen by the ILC design, also synchrotron
radiation photon stops and/or clearing
electrodes, in the ECLOUD code. 4.6 May 06
Update ECLOUD model parameters based on the
results of code benchmarking. 4.7 June 06
Develop 1st version of a new electron-cloud
build-up simulation program (or extend an
existing one) for correct 3-D modeling including
3-D space charge, 3-D geometry and possibly 3-D
time-varying external fields. Consider eventual
extension towards a self-consistent
electron-cloud build-up instability model.
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Goal 5. Application of the codes to predict the
effect in the damping ring designs Milestones 5.
1 October 05 Simulate electron-cloud build up
with ECLOUD code for a 3-km, 6-km and 17-km
damping ring 5.2 October 05(?) Compare results
with at least one code from POSINST (SLAC/LBNL)
, PEI (KEK) and possibly CLOUDLAND (BNL/SLAC)
5.3 October 05 Simulate instability thresholds
with HEADTAIL for a 3-km, 6-km and 17-km damping
ring and compare them with predicted electron
densities 5.4 June 06 Estimate the importance of
incoherent emittance growth due to electron
cloud for the different damping-ring designs 5.5
December 06 Repeat electron cloud build-up and
instability simulations using the chamber
material properties and the vacuum chamber
layout determined or developed in the two other
parts of this work package
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Incoherent blow up?
solenoids in west arc off
beam size increase with current below threshold
4 trains, 200 bunches/train, 3 bucket spacing
TMCI threshold
H. Fukuma, ECLOUD04
KEKB beam size vs. current
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International Context (ILC Collaboration)
EUROTeV WP3 e-cloud study provides European
contribution to ILC WG3 Task Force 6
Electron-Cloud EffectsCo-ordinatorsKazuhito
Ohmi (KEK) ohmi_at_post.kek.jpMauro Pivi (SLAC)
mpivi_at_slac.stanford.eduFrank Zimmermann (CERN)
frank.zimmermann_at_cern.ch
goal documented baseline configuration for ILC
damping rings by end 2005 e-cloud task force
carries out specific studies of the various
options availableaddressing the
question possibly this could be extended to
include the study of countermeasures, as
critical SEY yield depends on them
Specify SEY limits to prevent electron cloud
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International Context (ILC Collaboration) contd
There is strong common interest with ILC WG3
Task Force 7 Fast-Ion EffectsCo-ordinatorsDani
el Schulte (CERN) ohmi_at_post.kek.jpEun-San Kim
(POHANG) eskim1_at_potech.ac.krFrank Zimmermann
(CERN) frank.zimmermann_at_cern.ch
goal documented baseline configuration for ILC
damping rings by end 2005 fast-ion task force
carries out specific studies of the various
options availableaddressing the question
Specify vacuum requirements to prevent fast-ion
effects
Indeed one of the deliverables of EUROTeV WP3 is
Report on impact of e-cloud and fast ion
instabilities on DR performance, including
recommendations for controlling the effects.
though there is no objective and no milestone
associated with ion effects
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Benchmarking of ECLOUD and POSINST in ILC DR
wiggler
POSINST
Simulated electron cloud density with POSINST
(SEY params ex. dmax1.1-1.5, emax190eV)
photoelectron rate is 0.007 electrons per meter
per positron wiggler field described by
Cartesian model rectangular chamber with
semi-axes a x b16x9mm and two antechambers 10mm
full size on both sides Hilleret model for e-
reflection.
Mauro Pivi / SLAC
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Benchmarking of ECLOUD and POSINST in ILC DR
wiggler
e- line density m-1
ECLOUD
dlge/ds0.007 m-1
dlge/ds0.0007 m-1
time s
Simulated electron cloud density with ECLOUD (SEY
params ex. dmax1.3, emax190eV) photoelectron
rates are 0.007 and 0.0007 electrons per meter
per positron wiggler field described by
Cartesian model rectangular chamber with
semi-axis a x b16x9mm Hilleret model for e-
reflection.
Frank Zimmermann / CERN
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one possible countermeasure the electron-cloud
killer
NEG-coated 100-mm copper-foil electrode with
100-V bias voltage
proposal by P. McIntyre (paper at
PAC05) prototype built at Texas AM, shipped to
CERN this month
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EUROTeV WP3 Work done in the 1st six months

• started benchmarking ECLOUD-POSINST codes
• M. Pivi, F. Zimmermann (see above)
• started compiling ILC DR parameters for
• DR configuration study R. Wanzenberg
• benchmarked electron-cloud build-up simulations
• with data from SPS strip detector
• D. Schulte
• implemented (preliminary) wiggler models for
• DAFNE in ECLOUD code
• C. Vaccarezza, F. Zimmermann

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ILC DR Parameters
data compiled by R. Wanzenberg
Conflicting data exists Andy Wolskis ILC DR
Megatables Mauro Pivis PAC05 e-cloud
paper
betatron tunes differ by various integers for
same circumference
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ILC DR Parameters 2
data compiled by R. Wanzenberg
? Beta in the arc
Design of the vacuum chamber ? Ante chamber ?
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ILC DR wiggler
Different models for the wiggler field a)
dipole b) c)
Different parameters NLC Wiggler Peak field
2.2 T Period 270 mm Gap 18 mm TESLA
Wiggler Peak field 1.7 T Period 400 mm Gap 20 mm
Wolski- Venturini
Halbach
Vacuum chamber design with ante-chamber ? Reduced
number of photons
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SEY characterized by dmax, emax, and R
R. Cimino, I. Collins
dmax
R
emax
2003 laboratory data indicated that elastic
reflection probability approaches 1 for zero
incident energy and is independent of dmax
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SPS strip detector for e-cloud code benchmarking
J.M. Jimenez
picture of the collecting plates
Schematic view of a strip-detector showing the
position of the collecting strips with respect
to the beam.
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typical measurement with SPS strip detector
J.M. Jimenez
Spatially distributed flux of the electrons
varying with the number of injected 72-bunch
trains and with the ramp in energy.
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simulation parameters for SPS strip detector
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SPS benchmarking, strip detector simulation
Daniel Schulte
two different bunch train spacings two
different pressures (40 ntorr and 4 ntorr)
surface conditions (dmax, R) and detector
properties are uncertain constrain
parameters by benchmarking multiple measurements
change distance between trains use
relative measurements
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flux for 1 vs. 2 bunch trains
Daniel Schulte
measured F2/F14
(M. Jimenez)
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Daniel Schulte
2.05 ms vs 0.225 ms spacing
measured F2.05/F0.2250.60
4 bunch trains
(M. Jimenez)
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Daniel Schulte
absolute flux
measured F0.9 mA
2 bunch trains
(M. Jimenez)
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combined (1) 12 trains, (2) two spacings, (3)
absolute
Daniel Schulte
three curves intersect at dmax1.35, R0.3 flux
at later times (F0.3 mA) dmax1.2 was
reached
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robustness check same simulation, but assuming
that e- with vertical kinetic energy of less
than 10 eV are not detected
Daniel Schulte
relative curves (1) and (2) still intersect at
dmax1.35, R0.3 absolute flux does not agree
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dependence on assumed vacuum pressure vacuum
which is 10 times better (4 nTorr) or worse (400
nTorr)
4 nTorr
400 nTorr
three combinations of dmax and R can explain
measurement maximum value of R 0.7
no single combination of dmax and R can explain
measurement
all these simulations assumed elliptical
chamber cross check with a rectangular chamber
yielded dmax1.3, R0.15 (instead of dmax1.35,
R0.3 for elliptical boundary)
conclusions results sensitive to pressure,
chamber geometry, etc., variation dmax1.4-1.3,
R0.1-0.7
Daniel Schulte
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e-cloud modelling for DAFNE
lepton machine, in Europe, e-cloud effects,
wigglers (important!), ideal benchmark
(gt70 damping from wigglers)
DAFNE

• 1997 prediction of e-cloud in DAFNE
• no evidence until 2003 DAFNE reached 2.5 A e
  current w/o problem
• since 2003, e current limited to 1.2 A in
  collision by instability (10 ms rise time) with
  e-cloud signature (pressure rise, positive tune
  shift in e ring) w/o collision instability at
  500 mA
• sensitive to orbit, bunch current, injection
• conditions, transverse emittance
• instability strongly increases along train
• rise time faster than synchrotron period

grow-damp measurement 90 consecutive bunches
20 bucket gap beam current 500 mA
bunches at the train end75, 80, 85,90
A. Drago M. Zobov C. Vaccarezza
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Cristina Vaccarezza
DAFNE wiggler field after modification
measured By
By from bi-cubic spline fit implemented in ECLOUD
3 curves refer to y1 cm x -7, 0, 7 cm
Bz from spline fit implemented in ECLOUD
Bx from spline fit implemented in ECLOUD
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Cristina Vaccarezza
error??
DAFNE wiggler field before modification
By from bi-cubic spline fit tentatively
implemented in ECLOUD
3 curves refer to y1 cm x -6, 0, 6 cm
Bz from spline fit tentatively implemented in
ECLOUD
Bx from spline fit tentatively implemented in
ECLOUD
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e- build up in DAFNE wiggler 2002 2004 -
preliminary
OLD NEW wiggler, OLD beam parameters
NEW wiggler, OLD NEW beam parameters
little effect of change in wiggler field
large effect of beam parameters (new
ones being better)
dmax1.4 emax230 eV
dmax1.4 emax230 eV
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thanks to EUROTeV and CARE for supporting this
activity thanks to Susanna Guiducci for her
confidence and for providing the link to the ILC
WG3 thank you for your attention!