Collimator design and short range wakefields

Adriana Bungau

University of Manchester

CERN, Dec 2006

ILC-BDS spoilers

Must satisfy several competing requirements:

• Thickness: 0.5 and 1.0 r.l -> 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)-> reduces the

wakefield components induced by change in aperture• high electrical conductivity ->mitigates 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 ->rely heavily on simulation

Bunch charge: 2.1010 e-, energy=250 GeV

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 alloy111 9 290 255 255

1.0 r.l.

Ti alloy104 15 260 300 310

30 cm Cu 20 1.4 25000 25000 25600

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√2 6√2 2770 3180 3200

0.6 r.l.

Ti alloy111√2 9√2 560 450 435

1.0 r.l.

Ti alloy 58 11 720 760 770

30 cm Cu 20√2 1.4√2 60000 69000 70000

Benchmarking for simple titanium alloy targets

Bunch charge: 2.1010 e-, Energy=500 GeV

GEANT4 simulations of the spoilers

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

Choice of material:

Material r.l. T (K) Conductivity

(.m)-1

Ti6Al4V 3.56 1941 -

Copper 1.43 1358 6.0*10-7

Aluminium 8.9 933 3.8*10-7

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: 2*1010 e-

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.

Full metal spoiler

Ti alloy spoiler

width = 38 mmheight = 17 mmlength = 122.64 mmupper region = 21.4 mmangle = 324 mrad

Al spoiler

width = 38 mmheight = 17 mmlength = 154.64 mmupper region = 53.4 mmangle = 324 mrad

Cu spoiler

width = 38 mmheight = 17 mmlength = 109.82 mmupper region = 8.58 mmangle = 324 mrad

zy

x

Ti alloy Aluminium

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%

Instantaneous T rise

Fracture T (489 K) exceeded!

Copper

Depth T at 250 GeV T at 500 GeV

2 mm 1206 2438

10 mm 3060 7800

Difference 153% 219%

Instantaneous T rise

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

zy

x

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

Instantaneous T rise

Ti alloy-Graphite Aluminium-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%

Depth T at 250 GeV T at 500 GeV

2 mm 517 743

10 mm 330 850

Difference -36% 14%

Instantaneous T rise

Copper-Graphite

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 2 mm depth e.m. shower for one 250 GeV e- at 10 mm depth

Particle Multiplicities and Energy Spectra

Ti alloy-Graphite

Ti alloy-Graphite

Al-Graphite

Al-Graphite

Conclusion - collimator damage

• 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 ?)

Ti alloy - graphite spoiler is the best option

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 -> 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-2006-051)

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

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.

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 spreadCommissioning: Jan 2006 (4 old collimators) - SuccessfulPhysics: 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)

ESA – Experimental tests

- 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

- collimators fabricated and polished at RAL

Sandwich 2, slot 4

Reconstructed kick vs collimator position

good run: 1206

horizontal axis in mm, vertical axis in urad position of the BPMs

-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;

bad run: 1388

Next plans :

• data analysis work not complete-> reprocessing with new BPM calibration algorithm

• Manchester cluster set up for BPM recalibration - complete

• seven new collimator designs agreed for run3-ESA ->sent to manufacturing company

• new beam tests at ESA in 2007 with new collimators