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Collimator Damage Adriana Bungau The University of Manchester Cockcroft Institute “All Hands Meeting”, January 2006

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Collaboration between RAL, Manchester University and Daresbury Laboratory Goal: determine optimal material and geometry for ILC collimators in order to maximize the collimation efficiency and minimize the wakefield effects Investigate the heating effects caused by various patterns of energy deposit using ANSYS (G. Ellwood -RAL, G.Kourevlev –Manchester Univ.) Simulate the energy deposition in a spoiler of specified geometry due to a beam being mis-steered using FLUKA ( L. Fernandez – Daresbury) and Geant4 (A.Bungau – Manchester Univ. ) Cross-check these studies with Lewis Keller’s results on spoiler survival (SLAC) Study a range of geometry/material combinations that allows low wakefields and verify these experimentally What we do:

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Update report on material damage Geant4/Fluka results: Model of an isometric view of the collimator (geometry, material) Simulations of the energy deposition along z at several depths; distributions in various 2D projections of the energy density Calculations of the corresponding increase in temperature Kinetic energy of the outgoing particles Results passed on for ANSYS studies ANSYS results: Studies of steady state heating effects (3d isothermal contours-consistent) Comparation between ANSYS simulations and analytic calculations (good agreement) ANSYS used to predict stress induced in a 3d solid (apply to the collimator geometry)

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Collimator geometry (modelled with Geant4) Dimensions: x = 38 mm y = 17 mm z = 21.4 mm Z = 122.64 mm θ = 324 mrad Material: Ti alloy (Ti-6Al-4V) = 4.42 g/cm 3 melting temperature 1649 C° c = 560 J/kg C° z y x

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Beam profile Ellipsoid with x = 111 m y = 9 m Simulated particles: 10 4 electrons/bunch E = 250 GeV Energy cutoff: e - kinetic energy cutoff = 2.0 MeV ->2.9 mm range in Ti alloy e + kinetic energy cutoff = 2.0 MeV ->3.1 mm range in Ti alloy energy cutoff =100.4 KeV ->6.18 cm attenuation length in Ti alloy

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Energy deposition in Ti alloy at 2 mm depth the beam is sent through the collimator along z at 2 mm depth E dep max in the second wedge at ≈14 mm the mesh size should be smaller than the beam size for realistic results at z≈14 mm: max energy deposition is 3 GeV/2e-3 mm 3 -> ∆T = 215 K

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Energy deposition at 10 mm depth in Ti alloy the beam goes through the collimator at 10 mm depth max E dep at 10 mm depth is at ≈35 mm along z (second wedge) at z≈35 mm, the max E dep is 6.66 GeV/2e-3 mm 3 -> ∆T = 430 K

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

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Energy deposition at 16 mm depth in Ti alloy spoiler the beam is sent through the collimator at 16 mm depth max E dep is at ≈55 mm max E dep = 8 GeV/2e-3 mm 3 -> ∆T = 517 K

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e.m. shower for one 250 GeV e - at 16 mm depth

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Depth (mm) T for Ti T for Ti alloy 2226215 10452430 16581517 Summary L.Keller: e + : multiplicity ≈ 4 e - : multiplicity ≈ 4 e + : multiplicity ≈ 3

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Steering Condition Beam Size (µm) σ x σ y Max T 500 GeV CM Max T 1 TeV CM Max T 500 GeV CM Max T 1 TeV CM 0.6 rl Ti spoiler 28 61020288713802770 0.6 rl Ti spoiler 111 9302761290560 1.0 rl Ti Spoiler 104 15295 - 260720* Direct Hits on Spoilers L. KellerGeant 4 simulation Maximum ∆T/2x10 10 bunch at Hit Location, °C/bunch *with a spread in energy ∆E/E = 0.06 %

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Conclusion The instantaneous temperature rise at various depths were below the melting temperature of the Ti alloy ->collimators are not in danger in case of a direct hit from one bunch Little energy deposition in the material – a large fraction of the energy appears as photons emerging from the collimators Future plans Compare the Geant4 results with Fluka predictions Carry out a survey of materials (so far only Ti and Ti-6Al-4V were used) Pass on the energy deposits files for ANSYS studies ( RAL)

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