Latest ILC DR wiggler simulations

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Latest ILC DR wiggler simulations M. Pivi, T.
Raubenheimer, L. Wang (SLAC)
July, 2005
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ILC 17 km TESLA DR wiggler sections
Different models for the wiggler field a)
dipole b) c)
(TESLA) Wiggler Peak field 1.68 T Period 0.40
m Chamber semi-axis 16x9mm rectangular with
antechambers on both sides
Cartesian model, Halbach
Cylindrical expansion model, Wolski-Venturini
Vacuum chamber design with ante-chambers, Reduced
number of photons
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ILC 17 km TESLA DR wiggler sections
Figure 1 Horizontal, vertical, and longitudinal
magnetic field as a function of longitudinal
position for Cartesian (red dot symbols) and
cylindrical models (blue dot symbols) at x2 mm
and y 1 mm from the wiggler axis.
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Recent simulations Benchmarking of ECLOUD and
POSINST in ILC TESLA DR wiggler
Simulated electron cloud density with POSINST
vary SEY params (Ex. deltamax1.3, Emax190eV).
Photoelectrons rate is 0.007 electrons per meter
per positron. Wiggler field Cartesian model.
Rectangular chamber with semi-axis axb16x9mm and
two antechambers 10mm full size on both sides.
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Recent simulations Benchmarking of ECLOUD and
POSINST in ILC TESLA DR wiggler
dmax1.3
Simulated electron cloud density with POSINST
(SEY params deltamax1.3, Emax190eV).
Photoelectrons rate are 0.007 and 0.0007
photo-electrons per meter per positron. Wiggler
field Cartesian model. Rectangular chamber with
semi-axis axb16x9mm and two antechambers 10mm
full size on both sides.
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DR task 6 Specify SEY limits from the electron
cloud - working plan -

• Methodology
• Pertinent parameters for three different rings
  (17 km, 6 km and 3 km circumference)
  For some studies (e.g. electron-cloud build-up)
  it probably is not necessary to study every
  lattice in detail, but pick one in each
  circumference.
• Electron cloud build up is simulated for the
  different regions (arcs, wigglers, straights)
  considering different secondary emission yields.
• For the wigglers simulations the field can be
  modeled at various levels of sophistication, and
  the importance of refined models has to be
  explored
• Single-bunch wake fields and the thresholds of
  the fast single-bunch TMCI-like instability are
  estimated
• Multi-bunch wake fields and growth rates are
  inferred from e-cloud build up simulations
• Electron induced tune shifts will be calculated
  and compared
• Predictions of electron build up from different
  simulation codes are compared
• Implemented in the simulations will be
  countermeasures which may be proposed as the ILC
  DR design evolves.

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Specify SEY limits from the electron cloud -
working plan for task 6 -
Expressions of interest and available
tools Build-up simulation codes are PEI (KEK),
POSINST (LBNL/SLAC), ECLOUD (CERN), and CLOUDLAND
(BNL/SLAC). Instability simulation codes are
PEHTS (KEK) and HEADTAIL (CERN) for single-bunch
instabilities, and PEI-M for multi-bunch
instabilities (KEK). Multi-bunch wake fields can
be extracted from POSINST and ECLOUD. There also
exists a single-bunch instability code written by
Y. Cai at SLAC. DESY, INFN, and CERN are
collaborating in the EUROTeV WP3 ECLOUD subtask,
the goals of which overlap with the ILC WG3
electron-cloud task. Rainer Wanzenberg (DESY)
has started a compilation of ring and beam
parameters. Further contributions are highly
welcome! Comparisons with existing machines A
benchmarking program is ongoing at the CERN SPS
and at DAFNE, in addition to PSR, PEP-II and
KEKB, and can support the predictions.
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Future Directions

• ILC DRs electron cloud build-up simulation
  benchmarking between CERN, SLAC, KEK codes. Need
  to
• Prioritize DRs from list for simulations
• Use common SEY model/s. Sensitivity studies.
• Electron cloud collective instability
  simulations.
• By October 2005 task force 6 Co-ordinators
  deliver the information that will be necessary
  for making a DR configuration selection.

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Previous simulations

• Following previous set of build-up simulations
  using POSINST, with previous ILC DR parameters
• Note
• - SEY thresholds (with this particular SEY model)
• Dependence of cloud density with vacuum chamber
  size (need to choose standard DR vacuum chamber
  sizes for simulations comparison purposes)

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Previous simulations Generation in the DR arcs
Fixed SEY dmax1.4 and varied vertical
chamber size
Simulations electron-cloud using POSINST 17km
long DR arc bend with antechamber. SEY threshold
occurs at peak SEY1.2-1.3. SEY model
parameterization assumes a variable Emax LHC
Proj.Rep-632
Arc bend simulations. Equilibrium electron
density as a function of the chamber size.
Assuming a fixed SEY peak dmax1.4
Beam pipe semiaxes Hor, Vert 22, 18 mm
Beam pipe semiaxes Hor 22 , Vert 18 to 30 mm
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Previous simulations SEY thresholds for the DR 6
km and 3 km
Electron density in units of e m3 as a function
of time for an arc bend in the 6 km DR option
(Left) and the 3 km DR option (Right), assuming a
chamber radius 22mm and including an antechamber
design (full height h10mm).
The SEY thresholds for the development of an
electron cloud in the dipole regions are dmax
1.11.2 for the 6 km DR and dmax 1.01.1 (!) for
the 3 km DR option.
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e-cloud expectations in the positron DR
Average neutralization levels and single-bunch
(SB) instability electron cloud density
thresholds for various damping ring options in
units of 1012 m-3. The average density
thresholds are for a ring modeled as a dipole
region.
E cloud Color coding

• - Arcs and wiggler sections aiming at SEY 1.2
• not an issue in long straight sections, provided
  a good coating (TiN, TZrV NEG) with SEY lt 1.9.
  Large chamber size.