Merlin A C++ Class Library for Collimation Studies 0 / 174 H. Rafique, R. Barlow, J. Molson

Ingredients The LHC The LHC Beam Collimation – what? Collimation – why? Merlin Future 1 / 174

The Large Hadron Collider Circumference = km Nominal Beam Energy = 7 TeV (proton) Nominal Collision CoM Energy = 14 TeV (proton – proton) Nominal stored energy of beams = 350 MJ Ultra High Vacuum < 1E-9 mbar Superconducting NbTi Magnets – up to 8.33T Supercooled via 700,000 litres of superfluid 1.9K Largest cryogenic centre in the world 1232 main dipoles (bending magnets) ~850 quadrupoles (focussing magnets) ~6200 higher order correcting magnets 2 / 174

3 / 174 The LHC

4 / 174 The LHC  Injection from SPS 450 GeV  Beam accelerated using MHz RF cavities  Dipole magnets operate up to 8.33T  Quads & other magnets focus and correct beam optics 2009: E = 3.5 TeV 2012: E = 4 TeV 2014: E = 7 TeV Per beam

5 / 174 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

6 / 174 Beam Halo & Blow Up The 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: TeV, GeV

7 / 174 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

8 / 174 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

9 / 174 Crossing in IP1 (ATLAS)

10 / 174 Collimation Hardware Required efficiency > 99.9% (No of absorbed protons : No that can reach normalised mechanical aperture at 10 σ) [1] < % 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

11 / 174 Merlin

12 / 174 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();

13 / 174 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 Potentials AcceleratorModelConstructor* 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();

14 / 174 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);

15 / 174 Materials  Collimator interactions depend on material  Collimators can have materials from the StandardMaterials database or user made materials MaterialProperties* Uo = new MaterialProperties (Atomic Mass, Atomic Number, Sigma_E, Sigma_I, Sigma_R, dEdx, Radiation Length, Density, Conductivity, MeanExcitationEnergy ); MaterialProperties* Be = new MaterialProperties ( , 4, 0.069, 0.199, , 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();

16 / 174 Beam  Defining a beams properties, from which a bunch is constructed BeamData mybeam; mybeam.charge = 1.31e11; mybeam.beta_x = * meter; mybeam.beta_y = * meter; mybeam.emit_x = * e-10 * meter; mybeam.emit_y = * e-10 * meter; mybeam.sig_z = 75.5 * millimeter; mybeam.sig_dp = ; mybeam.p0 = 7000*GeV; mybeam.yp0 = 0; mybeam.xp0 = 0; mybeam.x0 = 0; mybeam.y0 = 0; mybeam.alpha_x = * meter; mybeam.alpha_y = * meter; int no_part = 1E6; ParticleBunch* myInitialBunch = ParticleBunchConstructor (mybeam, n0_part, Distribution).ConstructParticleBunch();

17 / 174 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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19 / 174 The Future of the LHC 2013 Shutdown: upgrade to design E = 7 TeV and L = 1 x cm 2 s HiLumi LHC: Increased L 5 x current design L = 5 x cm 2 s -1 New hardware e.g. Crystal Collimators?

174 / 174 Proton – Lead ion collision, ALICE Acknowledgements Prof. Roger Barlow Huddersfield James Molson Manchester Dr. Stefano Redaelli Dr. Roderik Bruce Dr. Valentina Previtali Elena Quarenta CERN BE-ABP NGACDT EPSRC Thank You