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R. R. R.

• R. Bruce

ce, R. R.W. Assmann nn Bruce ce, R. R.W. Assmann nn

Ackno knowledg wledgemen ment: A. R Rossi, M. Giovanno nnozz zzi

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:
• R. Bruce 2011.03.23

IP1 TCTs No losses on aperture in the detector!

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

• R. Bruce 2011.03.23

No losses in detector at No losses in detector at beam stay clear radius beam stay clear radius

Cleaning with injection optics Cleaning with injection optics – higher energies after ramp higher energies after ramp

• R. Bruce 2011.03.23

3.5 TeV, intermediate collimator settings 7 TeV, nominal collimator settings

No losses in detector at No losses in detector at beam stay clear radius beam stay clear radius

Collision optics Collision optics – pencil beam on TCT pencil beam on TCT

• Example: 7 TeV, nominal

collimator settings, β*=0.55m

• R. Bruce 2011.03.23

No losses in detector at No losses in detector at beam stay clear radius beam stay clear radius w.r.t TCT

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