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Outline Outline SixTrack – introduction • Simulation scenarios • Results for injection optics • Results for collision optics • Conclusions • R. Bruce, 2011.03.23

SixTrack SixTrack Thin lens optical particle tracking element by element • Lattice including crossing and separation created with MAD-X • Special Monte Carlo routine in collimator (K2), taking into account • Multiple Coulumb scattering • Ionization • Point-like elastic and inelastic scattering • Single diffractive scattering included but factor 2-3 difference w.r.t. FLUKA • (SD not expected to be important for tungsten collimators) 200 turns simulated • Checks with 10cm precision if particles hit the aperture • Assumptions on halo used to create starting distribution • Impact parameter simulated in other studies • Diffusion mechanisms not important over 200 turns • Too CPU-intense to track the full beam – only halo tracked • R. Bruce 2011.03.23

Studied simulation scenarios Studied simulation scenarios Cleaning with injection optics • β *=11 m • 450 GeV, 3.5 TeV and 7 TeV considered, hor. and ver. • Starting distribution: pencil beam on primary collimator • Previous assumption: if we see no effect unsqueezed, we should be • safe in other conditions. Not true, due to additional outscattering from TCTs when squeezed Collision optics – possible large-angle scattering in TCTs • considered Starting distribution: pencil beam hitting TCT • In all simulations: • aperture model updated. Range of different apertures in ATLAS used. • 2.25 cm (mechanical radius), 1.545 cm (beam stay clear), lower values Perfect machine except IP1 pipe (most pessimistic case) • R. Bruce 2011.03.23

Cleaning with injection optics Cleaning with injection optics – 450 450 GeV GeV Example: B1 horizontal halo. Similar results for other planes and • beam. Losses around the ring for r=1.545cm: No losses on aperture in the detector! IP1 TCTs R. Bruce 2011.03.23

Cleaning with injection optics Cleaning with injection optics – 450 450 GeV GeV Local cleaning inefficiency (fraction of total particles lost locally per m) in the ATLAS beam pipe No losses in detector at No losses in detector at beam stay clear radius beam stay clear radius R. Bruce 2011.03.23

Cleaning with injection optics Cleaning with injection optics – higher energies after ramp higher energies after ramp 7 TeV, nominal collimator settings 3.5 TeV, intermediate collimator settings No losses in detector at No losses in detector at beam stay clear radius beam stay clear radius R. Bruce 2011.03.23

Collision optics Collision optics – pencil beam on TCT pencil beam on TCT Example: 7 TeV, nominal • collimator settings, β *=0.55m w.r.t TCT No losses in detector at No losses in detector at beam stay clear radius beam stay clear radius R. Bruce 2011.03.23

Conclusion Conclusion Injection (0.45, 3.5, 7 TeV), collision optics (3.5, 7 TeV) studied, • scan over beam pipe radius in each scenario In terms of cleaning, the most critical case is squeezed optics and • tight TCT settings Scattered particles only hit the beam pipe when radius is decreased by • factor 2 or more below beam stay clear Machine protection: • Asynchronous dump for collimator hierarchy: even in the most • pessimistic case (mechanical arc aperture, aperture in experimental pipe given by n1 calculation by M. Giovannozzi in previous meeting): arc shadows detector pipe No issues with smaller pipe for collimation • Beam dump check by beam dump team (B. Goddard et al) • Injection: follow up by V. Kain • OK for smaller beam pipe from collimation for studied optics • R. Bruce 2011.03.23