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Status of BDSIM Simulation L. Nevay, S. Boogert, H. Garcia-Morales, S. Gibson, R. Kwee-Hinzmann, J. Snuverink Royal Holloway, University of London 17th October 2014 Beam Delivery Simulation • • • • • • Beam Delivery Simulation (BDSIM) Geant4 and C++ particle tracking code Developed for linear collider background simulation Combines fast in-vacuum tracking with Geant4 physics Simulates interaction of primaries with accelerator Tracks all secondary particles 2 Previous State of BDSIM • BDSIM being adapted for use with rings ― Namely LHC & HL-LHC • Existing LHC Lattice partially converted to BDSIM format ― Some elements missing / not implemented • No turn control -> Geant4 models don’t typically have rings • Offset between ends of model (~100μm x & y) • Single turn optics shown L. Nevay et. al, In MOPRO045, Proceedings of IPAC 2014 3 Progress Since Then • All elements in LHC lattice implemented ― With rotation ― Using collimator database ― All collimator materials set properly • Turn control ― Dynamic volume tracking user limits ― Terminate all particles once N turns completed • Offset solved ― ― ― ― Inherent to MADX model of LHC More accurate survey model investigated Over 250 extra items Naming and lengths inconsistent between the two • Lattice solved as periodic boundary ― Offset represents extremely small inaccuracy in model ― Insignificant compared to misalignments of all components 4 4TeV Model • • • • 2012 4TeV B1 in collision optics used as test machine Generic Geometry 3.5um rad emittance x & y 6σ Halo in one dimension, Gaussian in other ― No cropping at 3σ • Vertical halo as example here 45000 40000 35000 30000 25000 20000 15000 10000 5000 -100 0 -150 25000 20000 15000 10000 5000 0 -100 -50 -50 0 y 0 x 50 50 100 100 150 y x 5 Simulation Details • • • • • 650000 primaries 1000 jobs ~ 1.5 days on 150 node farm ~3 Gb output in root format 20GeV energy cut-off 6 4TeV Model Loss Maps E (GeV / 10cm) 650000 primaries S (m) from IR 1 7 E (GeV / 10cm) IR 7 Detail S (m) from IR 1 8 Comparison E (GeV / 10cm) BDSIM S (m) from IR 1 R. Bruce et. al, Phys. Rev. ST Accel. Beams 17, 081004 (2014) 9 107 10000 s 15000 20000 Entries 1e+09 Mean 1.943e+04 RMS 2391 25000 10 106 5000 S (m) 105 104 103 102 10 1 0 Number of Particle Impacts As A Function of S Models in Preparation • Aiming to reproduce 4TeV LHC with higher statistics • 4TeV 2012 for B2 as well • HL-LHC model • In all cases, would like numerical comparison with Collimation Team results • Underway with help of Hector & Regina at RHUL 11 Improving The Statistics • Profiling shows significant time for Geant4 processes ― Intersection with next volume ― Volume searching • Only <1% of CPU time spend on tracking functions ― NB. our tracking functions are much quicker than a Runge-Kutta integrator ― Not unexpected • Geant4 processes cannot be improved upon (by us) • Geant4 is primarily designed for detector simulation ― Omnidirectional / no directional preference ― Highly repetitive structure can be described programmatically ― Hierarchical • An accelerator does not make a good detector ― Repetitive, yet sufficiently unique throughout ― Flat hierarchy – gives very poor geometry navigation / volume searching 12 Tracker Factorisation • BDSIM creates a Geant4 model of an accelerator ― Uses generic geometry classes ― Model built dynamically based on input file / lattice description • Normal Runge-Kutta integrators / steppers are replaced ― By custom functions ― Known solutions for known magnetic fields • Geant4 handles all tracking management ― Great for scattered particles, secondaries etc ― Highly inefficient for primaries that spend long time tracking • Factorise tracking routines ― Use only routines until particle close to aperture or in collimator ― Switch to Geant4 13 BDSIM Tracker • • • • Tracking routines separated from Geant4 Model Particles initially tracked using tracker When close to aperture -> passed to normal BDSIM (G4) BDSIM uses exactly the same tracking routines ― Wrapped in Geant4 steppers for Geant4 model of accelerator • • • • Tracker development implementation in final stages Testing underway Interaction with BDSIM also being tested Expect significant improvement in speed -> statistics • Leads to more generic plug and play tracking 14 Geometry Improvement • Currently using generic geometry ― Cylindrically symmetric ― One material • Adding Geant4 geometry for an LHC Dipole & Quad ― Slightly simplified design ― Correct materials & therefore cross-sections • Also more realistic collimator design • Naturally leads to geometry libraries for BDSIM ― Truly generic ― Normal conducting ― Superconducting / LHC • Hector G-Morales working on this 15 Summary • • • • • LHC Model fully generated BDSIM developed for use with rings First loss maps from 4TeV LHC produced BDSIM loss maps include primaries and secondaries Close qualitative match between BDSIM simulation & measured losses • • • • Other models in preparations Quantitative comparison underway Improvements for increased statistics nearly complete More realistic generic geometries being implemented 16