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 -> 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

3. Bunch charge: 2.10 10 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 6138015602000 0.6 r.l. Ti alloy 111 9290255 1.0 r.l. Ti alloy 104 15260300310 30 cm Cu 20 1.425000 25600 Collimator design - GEANT4 Benchmarking for simple titanium alloy targets

4. Spoiler Beam size (  m)  X  Y EGS4  T (K) FLUKA  T (K) GEANT4  T (K) 0.6 r.l. Ti alloy 28√2 6√2277031803200 0.6 r.l. Ti alloy 111√2 9√2560450435 1.0 r.l. Ti alloy 58 11720760770 30 cm Cu 20√2 1.4√2600006900070000 Benchmarking for simple titanium alloy targets Bunch charge: 2.10 10 e -, Energy=500 GeV

5. GEANT4 simulations of the spoilers Two types of spoilers: a full metal spoiler a combination of metal and graphite Choice of material: Materialr.l.T (K)Conductivity ( .m) -1 Ti6Al4V3.561941 - Copper1.4313586.0*10 -7 Aluminium8.99333.8*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*10 10 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.

6. Full metal spoiler Ti alloy spoiler width = 38 mm height = 17 mm length = 122.64 mm upper region = 21.4 mm angle = 324 mrad 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 z y x

7. 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!

8. Copper Depth  T at 250 GeV  T at 500 GeV 2 mm 1206 2438 10 mm 3060 7800 Difference 153% 219% Instantaneous T rise

9. 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 z y 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

10. 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%

11. 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

12. 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

13. Particle Multiplicities and Energy Spectra Ti alloy- Graphite Al-Graphite

14. 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

15. 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)

16. NoNameTypeZ (m)Aperture 1CEBSY1Ecollimator37.26 ~ 2CEBSY2Ecollimator56.06 ~ 3CEBSY3Ecollimator75.86 ~ 4CEBSYERcollimator431.41 ~ 5SP1Rcollimator1066.61x99y99 6AB2Rcollimator1165.65x4y4 7SP2Rcollimator 1165.66x1.8y1.0 8PC1Ecollimator1229.52x6y6 9AB3Rcollimator1264.28x4y4 10SP3Rcollimator1264.29x99y99 11PC2Ecollimator1295.61x6y6 12PC3Ecollimator1351.73x6y6 13AB4Rcollimator1362.90x4y4 14SP4Rcollimator1362.91x1.4y1.0 15PC4Ecollimator1370.64x6y6 16PC5Ecollimator1407.90x6y6 17AB5Rcollimator1449.83x4y4 NoNameTypeZ (m)Aperture 18SP5Rcollimator1449.84x99y99 19PC6Ecollimator1491.52x6y6 20PDUMPEcollimator1530.72x4y4 21PC7Ecollimator1641.42x120y10 22SPEXRcollimator1658.54x2.0y1.6 23PC8Ecollimator1673.22x6y6 24PC9Ecollimator1724.92x6y6 25PC10Ecollimator1774.12x6y6 26ABEEcollimator1823.21x4y4 27PC11Ecollimator1862.52x6y6 28AB10Rcollimator2105.21x14y14 29AB9Rcollimator2125.91x20y9 30AB7Rcollimator2199.91x8.8y3.2 31MSK1Rcollimator2599.22x15.6y8.0 32MSKCRABEcollimator2633.52x21y21 33MSK2Rcollimator2637.76x14.8y9 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.

17. 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)

18. 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

19. 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

20. 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