Collimator Design

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Collimator Design
Adriana Bungau The University of
Manchester, UK
Annual EuroTev meeting - Frascati, Italy, 23
- 25 January 2008
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Content

• Introduction
• - SWMD collaboration
• - Collimator design - requirements
• Wakefield Measurements at SLAC-ESA
• - T480 experiment (collimators, beam
  parameters)
• - data analysis
• Collimator Damage Tests at ATF
• - test plan
• - schedulle
• - test equipment
• - Conclusion

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People - SWMD collaboration
Birmingham N.Watson, M Slater SFTF L.Fernandez,
G.Ellwood, J.Greenhalgh, B.Fell, S.
Appleton CERN G.Rumolo, D.Schulte,
A.Latina Lancaster D.Burton, J.Smith,
R.Tucker Manchester R.Barlow, A.Bungau,
R.Jones Darmstadt M.Karkkainen, W.Muller,
T.Weiland Also a strong collaboration with SLAC
(S.Molloy and M.Woods) for wakefield beam tests
and KEK for collimator damage.
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Requirements

• Significant problems
• short-range wakefields -gtlead to emittance
  dilution and beam jitter at the IP
• impact of a no of high density bunches can
  damage the spoilers

20 mrad

• 1. Spoiler geometry must reduce the wakefields to
  an acceptable level
• - long, shallow tapers of 20 mrad,
• - short flat upper section of 0.6
  r.l.
• - high conductivity surface coating
• the wakefield aspects of the design are
  addressed by experimental work centered around
  T480 project at SLAC-ESA and simulations with
  Gdfidl, Echo, Merlin, Placet (see Daniels talk)
• 2. Spoilers are required to survive 1 bunch at
  250 and 2 bunches at 500 GeV
• - use bulk material to minimise
  fractures, stress but optimal for heat flow
• - long path length for errant
  beams striking spoilers (large r.l graphite,
  beryllium etc)
• the design approach consider simulations
  with FLUKA, Geant4, EGS4, ANSYS and experimental
  work at KEK

0.6 r.l
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T480 experiment at SLAC-ESA
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Wakefield tests at SLAC-ESA
Aim measure the beam kick and compare it with
theoretical predictions and simulations
Beam Parameters at SLAC ESA and ILC
Beam size 100 um vertically 0.5-1.5 mm
longitudinally
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Designed Collimators
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ESA beamline
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Wakefield Box

• readings from each BPM were recorded together
  with the bunch charge and energy
• the kick was determined by performing a straight
  line fit to the upstream BPM and a separate one
  to fit the downstream ones
• the kick was calculated as the difference in the
  slopes of these fits

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Data analysis
Luis Fernandez - Daresbury
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a 324 mrad r 2 mm
Col. 1
a 166 r 1.4 mm
(r ½ gap)
Col. 6
Col. 3
a 324 mrad r 1.4 mm
Luis Fernandez - Daresbury
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Measured and calculated kick factor
Note quoted errors are estimates
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Collimator Damage Experiment at ATF
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Previous simulations
Aim the collimators can be damaged by the impact
of several bunches
Luis Fernandez - DL
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Stress wave
George Ellwood - RAL
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Purpose of the ATF test

• First run at ATF
• commisioning of the vacuum vessel, multi-axis
  mover, beam position and size monitors
• validate the mode of operation required for ATF
  tests
• measurement of the size of the damage region
  after individual beam impacts on test target
  (validation of FLUKA/ANSYS simulations of
  properties of material)
• ensure that the radiation protection
  requirements can be satisfied
• Next phase at ATF2
• measure the shock waves within the sample (VISAR
  or LDV) for single bunch and multiple bunches at
  ILC bunch spacing

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ATF Schedule
February 1st week - mover commisioning at
RAL 2nd week - installation at KEK 3rd week -
testing readout of beamline instrumentation 4th
week - measurement of samples - shock wave
measurements are planned at ATF2
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Test location
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Sample Target

• we would like to use a 100µm thick
• Ti-6Al-4V sample.
• the sample will probably be held
• between knife edge grips, similar to
• those illustrated.
• we could leave the top of the sample
• free from the grips.

Grip
Exposed edge of sample
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Reference Location
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Beam operation

• Once the reference edge has been found we will
  use the VG manipulator to step the sample
• a known distance in X and Y.
• We will then increase the charge and try to
  damage the sample.
• Then we will move the sample to a new location
  and try to damage with a different charge.
• We will continue to do this until we have
  performed all the planned tests.

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Fluka Predictions

• after testing, we intend to measure the are of
  damage of each impact with a Scanning Electron
  Microscope
• we will know the location of each damaged region
  because know the distance from the reference
  edge.
• this will help validate our predictions on beam
  damage.

Luis Fernandez - Daresbury
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SWMD Deliverable Summary

• Engineering design for ILC mechanical spoiler,
  including prototype evaluations of wakefield and
  beam-damage performance.
• Wakefields T480 at SLAC to evaluate wakefield
  performance of candidate spoiler designs,
  benchmarking calculations/modelling
• 16 jaw designs studied
• Beam damage detailed simulations of beam damage
  to spoiler jaws, including transient shockwave
  effects
• Achieved designs which satisfy beam damage
  requirements
• Phase 1 of beam test to verify modelling, starts
  at ATF 18 Feb. 2008
• Outcome of ongoing wakefield optimisation likely
  to require further iteration on candidate designs
• First conceptual design for mechanical spoiler
  design available, to report at EPAC08.

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SWMD Deliverables Summary

• Specification of requirements for LC spoilers -
  Complete
• Eurotev Report 2006-015 and ILC RDR
• Report on applicability of bench tests for ILC
  collimator design - Achieved
• Initial report EPAC06/EUROTeV Report 2006-056
• 2007 work ? method not suitable for quantitative
  tests of collimator jaws, had been identified as
  risk in EUROTeVAnnex I (amended).
• Final report in preparation.
• 3D simulation of wakefields for various candidate
  spoiler prototypes - Achieved
• For 16 ESA collimators, most recently using
  non-conformal moving mesh GdfidL
• Also for ECHO-3D at EPAC06
• Additional mesh dependence studies ongoing, esp.
  for smallest sz
• PAC07, EPAC06, EUROTeV-Reports 2006-055
  (GdfidL) and 2006-103 (MAFIA)
• Parametrised wakefield characteristics of
  spoilers for full simulation of the BDS
• See COLSIM WP

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SWMD Deliverables Summary

• Report on wakefield beam tests - Achieved
• Analysis of 2007 and 2006 T480 data for
  publication in progress, including
• BPM uncertainties/calibrations, bunch length
  monitoring
• Original plan was to use SCP and established
  instrumentation See PAC07, EPAC06, EUROTeV
  Reports 2007-044, 2006-059, 2006-060
• ECHO-3D new code suitable for LC regime (long
  structures, short bunches), with predictions
  verified by experimental data
• No public version so far
• Report on spoiler damage estimates and comparison
  with test beam data Partially achieved
• Simulations carried out with Fluka, Geant4 (EGS
  with Keller), see EPAC06 and EUROTeV Reports
  2006-015 and 2006-021
• FEA studies in ANSYS3D/Fluka of transient stress
  waves, see PAC07, EPAC06
• ATF beam test approved, see PAC07, scheduled for
  run 18 Feb 2008
• Optimal spoiler design to achieve requirements
  Partially achieved
• We have designs for material and geometry which
  can satisfy beam damage requirements
• Outcome of ongoing wakefield optimisation likely
  to require further iteration on candidate designs
• First conceptual engineering design produced

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Previous Simulations
Aim quantify collimators damage from impact of
several bunches
Temperature increase from 1 bunch impact
melting temp.
Exceeds
fracture temp.
Best candidate designs