MerlinA C++ Class Library for Collimation Studies

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H. Rafique, R. Barlow, J. Molson

IngredientsThe LHC

The LHC Beam

Collimation – what?

Collimation – why?

Merlin

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The Large Hadron Collider

Circumference = 26.659 kmNominal Beam Energy = 7 TeV (proton)Nominal Collision CoM Energy = 14 TeV (proton – proton)Nominal stored energy of beams = 350 MJUltra High Vacuum < 1E-9 mbarSuperconducting NbTi Magnets – up to 8.33TSupercooled via 700,000 litres of superfluid He @ 1.9KLargest cryogenic centre in the world1232 main dipoles (bending magnets)~850 quadrupoles (focussing magnets)~6200 higher order correcting magnets

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The LHC

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The LHC Injection from SPS 450 GeVBeam accelerated using 400.8 MHz RF cavitiesDipole magnets operate up to 8.33TQuads & other magnets focus and correct beam optics

• 2009: E = 3.5 TeV• 2012: E = 4 TeV• 2014: E = 7 TeVPer beam

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The LHC Beam ‘Beam’ consists of many ‘bunches’ of particles (usually protons)

The bunch distribution is approximately gaussian

Beam halo refers to the gaussian tails i.e. particles with amplitude larger than given aperture size

x

y

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Beam Halo & Blow UpThe beam halo is populated due to various phenomena:

EM fields from: Counter-rotating beam

Particles in the bunch scatter off of: Other bunch particles Coasting beam Gas in the vacuum Apertures

Other: Synchrotron radiation, power radiated:3.9 kW @ 7 TeV, 66 mW @ 450 GeV

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Collimation – what?OED: Collimator: A device for producing a parallel beam of rays or radiation.

In this case: removal / cleaning of unwanted particles from the accelerator

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Collimation – why?Protect superconducting magnets – avoid quenches

Max beam loss at 7 TeV (1% of beam over 10s) = 500 kW

Quench limit of SC LHC magnet = 8.5 W/m [1]

Remove ‘stray’ particles before collision

Act as emergency beam dump – TCDQ

Protect valuable ‘triplet’ quadrupoles used to maximise luminosity at Interaction Points[1] R. Aßmann,The Final LHC Collimation system, EPAC06

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Crossing in IP1 (ATLAS)

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Collimation HardwareRequired efficiency > 99.9% (No of absorbed protons : No that can reach normalised mechanical aperture at 10 σ)[1]

< 0.00002% of protons hitting the collimators may escape to impact upon a SC magnet [2]

System comprises of ~140 collimators / absorbers in IR3 and IR7

[1] R. Aßmann et al. Requirements for the LHC collimation system, CERN Proj. Rep. 599 [2] G. Robert-Demolaize, CERN Thesis 2006-069

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Merlin

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MAD Interface MAD .tfs table output Construct accelerator Useful for large accelerators (i.e. LHC)

MADInterface* myMADInterface = new MADInterface (“input.tfs”, EnergyInGeV);

AcceleratorModel* myModel = myMADInterface->ConstructModel();

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Accelerator Model Can be created from XTFF or MAD Interface Can be created from Accelerator Components in user code Once created can be further modified and manipulated e.g. alignment errors

added Each element has an associated EM Field, Geometry, Aperture and Wake

PotentialsAcceleratorModelConstructor* myAccCtor = new AcceleratorModelConstructor();myAccCtor->NewModel();

Quadrupole* quad = new Quadrupole( “name”, Length, K1 );myAccCtor->AppendComponent( *quad );

Collimator* coll = new Collimator (“coll”, Length, Material, ScatteringProcess, momentum);Aperture* ap = new CircularAperture( .0002 );coll -> SetAperture( ap );myAccCtor -> AppendComponent( *coll );

AcceleratorModel* mymodel = myAccCtor -> GetModel();

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Physics Processes Can apply additional physics at selected elements and positions Scattering at collimators when particle amplitude > aperture Synchrotron radiation Wakefields Stepping managed by trackers

ScatteringModel* myScatter = new ScatteringModel;myScatter -> AddProcess( new Process() );myScatter -> AddProcess( new Inelastic() );

CollimateProtonProcess* myCollimateProcess = new

CollimateProtonProcess(0,7);myCollimateProcess->ScatterAtCollimator(true);

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Materials Collimator interactions depend on material Collimators can have materials from the StandardMaterials

database or user made materialsMaterialProperties* Uo = new MaterialProperties (Atomic Mass, Atomic Number, Sigma_E, Sigma_I, Sigma_R, dEdx, Radiation Length, Density, Conductivity, MeanExcitationEnergy );

MaterialProperties* Be = new MaterialProperties (9.012182, 4, 0.069, 0.199, 0.000035, 1.594, 65.19, 1.848, 3.08E7, (63.7*eV));Be.PrintTable();

Materials mix1;mix1.StandardMaterials();

mix1.MakeMixture (“Mix1”, “Al Cu W”, 1, 2, 3, 77., 56.);mix1.PrintTable();

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Beam Defining a beams properties, from which a bunch is constructed

BeamData mybeam;

mybeam.charge = 1.31e11;mybeam.beta_x = 0.5495121695 * meter; mybeam.beta_y = 0.5498820579 * meter;mybeam.emit_x = 33.640 * 5.026457122e-10 * meter; mybeam.emit_y = 33.64 * 5.026457122e-10 * meter;mybeam.sig_z = 75.5 * millimeter; mybeam.sig_dp = 0.000113;mybeam.p0 = 7000*GeV;mybeam.yp0 = 0; mybeam.xp0 = 0; mybeam.x0 = 0; mybeam.y0 = 0;mybeam.alpha_x = -0.0001721885021 * meter;mybeam.alpha_y = -0.0004654580947 * meter;

int no_part = 1E6;

ParticleBunch* myInitialBunch = ParticleBunchConstructor (mybeam, n0_part, Distribution).ConstructParticleBunch();

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Tracker Takes bunch and beamline inputs, tracks bunch along the

beamline Can use specific integrator sets such as TRANSPORT, Thin Lens,

and Symplectic Can step along the accelerator lattice and within accelerator

components

ParticleBunch* myInitialBunch = ParticleBunchConstructor (mybeam, n0_part, Distribution).ConstructParticleBunch();

ParticleTracker* mytracker = new ParticleTracker (mymodel ->GetBeamline(),

myInitialBunch);mytracker -> AddProcess (myCollimateProcess );

ParticleBunch* myFinalBunch;

myFinalBunch = mytracker -> Track (myInitialBunch);

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The Future of the LHC2013 Shutdown: upgrade to design E = 7 TeV and

L = 1 x 1034 cm2 s-1

2020 HiLumi LHC: Increased L 5 x current design L = 5 x 1034

cm2 s-1

New hardware e.g. Crystal Collimators?

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Proton – Lead ion collision, ALICE 13.09.12

Acknowledgements

Prof. Roger BarlowHuddersfield

James MolsonManchester

Dr. Stefano RedaelliDr. Roderik BruceDr. Valentina PrevitaliElena Quarenta

CERN BE-ABP

NGACDTEPSRCThank You