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 -> 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. Collimator design - GEANT4 Benchmarking for simple titanium alloy targets Bunch charge: 2.1010 e-, energy=250 GeV

4. Benchmarking for simple titanium alloy targets Bunch charge: 2.1010 e-, Energy=500 GeV

5. GEANT4 simulations of the spoilers 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- Two types of spoilers: • a full metal spoiler • a combination of metal and graphite Choice of material: 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. y z x 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

7. Instantaneous T rise Aluminium Ti alloy Fracture T (489 K) exceeded!

8. Instantaneous T rise Copper

9. y z x 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

10. Instantaneous T rise Aluminium-Graphite Ti alloy-Graphite

11. 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 10 mm depth e.m. shower for one 250 GeV e- at 2 mm depth

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

14. 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 ?)

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. 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 - 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

19. 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

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