Collimator design and short range wakefields

1
Collimator design and short range wakefields

• Adriana Bungau
• University of Manchester

CERN, Dec 2006
2
ILC-BDS spoilers

• Must satisfy several competing requirements
• Thickness 0.5 and 1.0 r.l -gt avoids particle
  multiplication in e.m.
• showers and high energy density
• Survivable ( 1 bunch at 250 GeV and 2 bunches at
  500 GeV)
• Include tapers section (leading and trailing
  tapers)-gt reduces the
• wakefield components induced by change in
  aperture
• high electrical conductivity -gtmitigates the
  resistive wall effects

Understanding the effect the concentrated energy
deposition has on the collimator material is an
important design consideration
Impossible to test the ILC candidate spoiler in
the exact beam conditions of size and energy as
the ILC -gtrely heavily on simulation
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Collimator design - GEANT4
Benchmarking for simple titanium alloy targets
Spoiler Beam size (?m) ?X ?Y EGS4 ?T (K) FLUKA ?T (K) GEANT4 ?T (K)
0.6 r.l. Ti alloy 28 6 1380 1560 2000
0.6 r.l. Ti alloy 111 9 290 255 255
1.0 r.l. Ti alloy 104 15 260 300 310
30 cm Cu 20 1.4 25000 25000 25600
Bunch charge 2.1010 e-, energy250 GeV
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Benchmarking for simple titanium alloy targets
Spoiler Beam size (?m) ?X ?Y EGS4 ?T (K) FLUKA ?T (K) GEANT4 ?T (K)
0.6 r.l. Ti alloy 28v2 6v2 2770 3180 3200
0.6 r.l. Ti alloy 111v2 9v2 560 450 435
1.0 r.l. Ti alloy 58 11 720 760 770
30 cm Cu 20v2 1.4v2 60000 69000 70000
Bunch charge 2.1010 e-, Energy500 GeV
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GEANT4 simulations of the spoilers

• Two types of spoilers
• a full metal spoiler
• a combination of metal and graphite

Beam profile - at energy 250 GeV ?x 111
?m ?y 9 ?m - at energy 500 GeV ?x
78.48 ?m ?y 6.36 ?m Charge 21010 e-
Choice of material
Material r.l. T (K) Conductivity (?.m)-1
Ti6Al4V 3.56 1941 -
Copper 1.43 1358 6.010-7
Aluminium 8.9 933 3.810-7
The beam was sent through the collimators at 2
depths 2mm and 10 mm from the top at beam energy
250 GeV and 500 GeV for each depth.
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Full metal spoiler
Al spoiler width 38 mm height 17 mm length
154.64 mm upper region 53.4 mm angle 324
mrad
Cu spoiler width 38 mm height 17 mm length
109.82 mm upper region 8.58 mm angle 324
mrad

• Ti alloy spoiler
• width 38 mm
• height 17 mm
• length 122.64 mm
• upper region 21.4 mm
• angle 324 mrad

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Instantaneous T rise
Aluminium
Ti alloy
Depth ?T(K) at 250 GeV ?T(K) at 500 GeV
2 mm 376 827
10 mm 818 1951
Difference 117 135
Depth ?T(K) at 250 GeV ?T(K) at 500 GeV
2 mm 201 372
10 mm 276 586
Difference 37 58
Fracture T (489 K) exceeded!
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Instantaneous T rise
Copper
Depth ?T at 250 GeV ?T at 500 GeV
2 mm 1206 2438
10 mm 3060 7800
Difference 153 219
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Metal-graphite spoiler

• same dimensions as Ti alloy
• graphite prism
• z 100.23 mm long
• offset from spoiler centre
• ?z 10.18 mm
• ?y 0.16 mm

same dimensions as for Al graphite prism z
100.23 mm long offset from spoiler centre ?z
26.07 mm ?y 0.16 mm
same dimensions as for Cu graphite prism z
100.23 mm long offset from spoiler centre ?z
3.76 mm ?y 0.16 mm
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Instantaneous T rise
Aluminium-Graphite
Ti alloy-Graphite
Depth ?T at 250 GeV ?T at 500 GeV
2 mm 238 456
10 mm 304 527
Difference 27 15
Depth ?T at 250 GeV ?T at 500 GeV
2 mm 190 352
10 mm 192 381
Difference 1 8
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Instantaneous T rise
Copper-Graphite
Depth ?T at 250 GeV ?T at 500 GeV
2 mm 517 743
10 mm 330 850
Difference -36 14
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Summary

• the combination of metal-graphite spoiler is a
  safer option ( the melting
• T was not reached in any of these cases)
• attractive candidates are TiAlloy-Graphite and
  Al-graphite spoilers

What about particle multiplicities and energy
spectra?
e.m. shower for one 250 GeV e- at 10 mm depth
e.m. shower for one 250 GeV e- at 2 mm depth
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Particle Multiplicities and Energy Spectra
Ti alloy-Graphite
Al-Graphite
Al-Graphite
Ti alloy-Graphite

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Conclusion - collimator damage
Ti alloy - graphite spoiler is the best option

• Energy deposition profile from Geant4/Fluka used
  for
• ANSYS studies at RAL (steady state, transient
  effects,
• fractures)
• Simulation studies are now written up (see
  EUROTeV reports)
• Beam damage test to follow (SLAC, CERN ?)

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Wakefield simulations with Merlin

• Current situation
• mathematical formalism developed by R. Barlow for
  incorporating higher order mode wakefields
• formalism implemented in the Merlin code
• SLAC beam tests simulated -gt good agreement
  between analytical calculations and experiment
• so far, only simple beamlines were studied (ie.
  Drift, Collimator, Drift)

Roger Barlow, Adriana Bungau - Simulation of
High Order Short Range Wakefields
(EUROTeV-Report-2006-05
1)
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• Next plans
• extend the studies to the ILC-BDS beamline (33
  collimators involved)
• interested in the emittance growth given by
  wakefield modes as a function of beam offset,
  bunch profile at IP
• work is in progress.

No Name Type Z (m) Aperture
1 CEBSY1 Ecollimator 37.26
2 CEBSY2 Ecollimator 56.06
3 CEBSY3 Ecollimator 75.86
4 CEBSYE Rcollimator 431.41
5 SP1 Rcollimator 1066.61 x99y99
6 AB2 Rcollimator 1165.65 x4y4
7 SP2 Rcollimator 1165.66 x1.8y1.0
8 PC1 Ecollimator 1229.52 x6y6
9 AB3 Rcollimator 1264.28 x4y4
10 SP3 Rcollimator 1264.29 x99y99
11 PC2 Ecollimator 1295.61 x6y6
12 PC3 Ecollimator 1351.73 x6y6
13 AB4 Rcollimator 1362.90 x4y4
14 SP4 Rcollimator 1362.91 x1.4y1.0
15 PC4 Ecollimator 1370.64 x6y6
16 PC5 Ecollimator 1407.90 x6y6
17 AB5 Rcollimator 1449.83 x4y4
No Name Type Z (m) Aperture
18 SP5 Rcollimator 1449.84 x99y99
19 PC6 Ecollimator 1491.52 x6y6
20 PDUMP Ecollimator 1530.72 x4y4
21 PC7 Ecollimator 1641.42 x120y10
22 SPEX Rcollimator 1658.54 x2.0y1.6
23 PC8 Ecollimator 1673.22 x6y6
24 PC9 Ecollimator 1724.92 x6y6
25 PC10 Ecollimator 1774.12 x6y6
26 ABE Ecollimator 1823.21 x4y4
27 PC11 Ecollimator 1862.52 x6y6
28 AB10 Rcollimator 2105.21 x14y14
29 AB9 Rcollimator 2125.91 x20y9
30 AB7 Rcollimator 2199.91 x8.8y3.2
31 MSK1 Rcollimator 2599.22 x15.6y8.0
32 MSKCRAB Ecollimator 2633.52 x21y21
33 MSK2 Rcollimator 2637.76 x14.8y9
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Wakefield Measurements at SLAC-ESA
Motivation to optimize the collimator design by
studying various ways of minimising wakefield
effects while achieving the required performance
for halo removal

• SLAC beam has similar parameters as for the ILC
  bunch for bunch charge, bunch length and bunch
  energy spread
• Commissioning Jan 2006 (4 old collimators) -
  Successful
• Physics first run Apr/May second run July (8
  new collimators CCLRC)
• People N. Watson, S.Molloy, J. Smith, A.Bungau,
  L. Fernandez, C.Beard,
• A.Sopczak, F.Jackson (optics modeller)

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ESA Experimental tests
- collimators fabricated and polished at RAL

- insert collimators in beam
path (x mover)
- move
collimator vertically (y mover)

- measure centroid kick to beam via BPMs

- analyse kick angle vs collimator
position
1500mm
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Reconstructed kick vs collimator position

• performed calibrations before each of the
  collimators (ie. a BMP calibration for each
  collimator to protect against any BPM drifts)
• monitored the beam size, length etc as such a
  long scan would allow larger drifts in these
  cases

Sandwich 2, slot 4
good run 1206
horizontal axis in mm, vertical axis in urad
position of the BPMs
bad run 1388
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• Next plans
• data analysis work not complete-gt reprocessing
  with new BPM calibration algorithm
• Manchester cluster set up for BPM recalibration
  - complete
• seven new collimator designs agreed for run3-ESA
  -gtsent to manufacturing company
• new beam tests at ESA in 2007 with new
  collimators