The HiLumi LHC Design Study is included in the High Luminosity LHC project and is partly funded by the European Commission within the Framework Programme 7 Capacities Specific Programme, Grant Agreement 284404.

Status of Loss Map Simulation with MERLIN Code

M. Serluca, R. Appleby, R. Barlow, J. Molson, A. Toader

Summary•MERLIN code• LHC optics calculation• LHC collimation and cleaning efficiency:

loss map• Impact of imperfections on loss map • Enhanced scattering physics model• Future plans and conclusion

MERLIN code• C++ Accelerator Physics library•Written by Nick Walter et al. (DESY), it was

initially used to simulate ground motion in the ILC beam delivery system and later for the main linac and damping rings• Now adapted for large scale proton collimation

simulation by Manchester and Huddersfield • Allows a modular design for different physics

processes

MERLIN code• Accelerator lattice design: can load directly from tfs table

output of MAD or XTTF format, the main classes for each elements of the machine are the AcceleratorComponent, EMField, Accelerator Geometry, Aperture, WakePotential • Bunch creation: can be generated anywhere along the

machine and with different phase space distributions • Particle tracker: particle and moment tracking, different

integrator sets can be specified, override specific integrators• Physics process: examples are wakefield, synchrotron

radiation, space charge and collimation, they can be applied at selected elements and positions

MERLIN code• Position errors: can misalign the position of every

elements in s, x, y and can adjust angular tilt. For the collimators is also possible to misalign and tilt the individual jaw • Field errors: can be added including additional multipoles• Parallel running: MPI protocol in order to run large

simulations using multiple physical machines with interconnects• Tracking, collimation etc. are independent on a per-

particle basis

LHC optics calculation with MERLIN• Thick-lens version V6.5.2012.seq

• Energy = 4TeV, en= 3.5 mm-mrad, dp/p = 0, sz =0

• Using beam 1 or beam 2 • b* for IP1 and IP5: 0.6 m• b* for IP2 and IP8: 3 m• Crossing Angle [mrad]: X1 = -145, X2 = -90, X5 =

145, X8 = -220• Parallel separation on at all IP: sep = +/- 0.65 mm

LHC optics calculation: IR5

Loss map: simulation setup• Optics setup: squeezed and separated beams

• Ideal machine: no imperfections and collimators aligned to orbit

• Beam1 horizontal pencil halo: a ring in x-x’ in the normalized space, 0 values for the vertical coordinates

• 6.4M particles simulated, beam halo injected at first horizontal primary collimator in IR7 (TCP.C6L7) and tracked for 200 turns

• Impact parameter = 1 mm and 10 cm longitudinal loss resolution

• Sixtrack like scattering mode

Loss map result with MERLINInefficiency definition:

Loss map result: IR7 zoom

Impact of lattice imperfection on loss map• Misalignment and magnetic errors on lattice elements

are introduced and corrected in MAD using the available correctors, then they are imported in MERLIN• The collimators are aligned to the ideal reference orbit• Simulations for uncorrected orbit show a different

distribution of the losses and can lead to the collimation hierarchy breaking• Simulations for corrected orbit show a little impact on

the loss maps

Impact of imperfections on loss map

• Unavoidable errors affect any accelerator and can further degrade the cleaning efficiency• Random errors with Gaussian distribution cut

at 3 s are generated inside MERLIN for collimator-jaw alignment and tilt angular errors

Impact of collimator imperfections on loss map • RMS error on gap center with respect to the

beam orbit: 50 mm• RMS error on gap size: 0.1 s• RMS error on jaw angle with respect to the

beam orbit: 200 mrad• Jaw flatness error: not yet implemented•Non ideal closed orbit: not yet evaluated

Impact of collimator imperfections on loss map (preliminary results)• For misalignment, tilt and gap error an increase

of a factor 2 in the highest cold loss was found with respect to the ideal case• Next step is the introduction of the

deformation jaw and the evaluation the impact of the combined effect of collimators and lattice errors

Enhanced scattering physics•More accurate simulations of the losses in the

dispersion suppressor need a detailed knowledge of the scattering physics processes in the bulk jaw material• New models of proton-proton interactions

have been developed, with the aim of expanding these to proton- nucleus interactions

Enhanced scattering physics: elastic• Elastic scattering will give an angular kick to the ongoing protons,

resulting in an increase of the beam halo and the possibility to be lost along the machine

• Use the model of Donnachie and Landshoff: arXiv:1112.2485v1 [hep-ph]

• Fit the existing pp and p-pbar data is possible because data exist on either side of the region of interest

The fit on elastic data is almost completed

Enhanced scattering physics: SD• Single Diffraction interaction on a nucleon will result in an angular kick and

energy loss to the outgoing proton

• The proton with an energy lower than the reference one will enter in the dispersion suppressor and will be subject to a larger orbit excursion.

• Use the model of Donnachie and Landshoff that involve soft QCD physics: arXiv:hep-ph/0305246v1

The fit on SD data is completed

Conclusion and future plans• We are developing the code MERLIN in order to produce loss

maps for collimation simulations for the current layout and future HiLumi upgrade • Results for 4TeV 2012 running show a good agreement with

sixtrack simulation results• The results with new elastic and SD model are in progress • A more detailed description of the effects induced by lattice

and collimator imperfections is almost ready• Near future works will be focused on advanced materials and

the improved optics • We are open to collaborate on new ideas for HiLumi project

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