1. Status of BDSIM Simulation L. Nevay, S. Boogert, H. Garcia-Morales, S. Gibson, R. Kwee-Hinzmann, J. Snuverink Royal Holloway, University of London 17 th October 2014

2. 2 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

3. 3 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

4. 4 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

5. 5 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

6. 6 Simulation Details 650000 primaries 1000 jobs ~ 1.5 days on 150 node farm ~3 Gb output in root format 20GeV energy cut-off

7. 7 4TeV Model Loss Maps 650000 primaries S (m) from IR 1 E (GeV / 10cm)

8. 8 IR 7 Detail S (m) from IR 1 E (GeV / 10cm)

9. 9Comparison R. Bruce et. al, Phys. Rev. ST Accel. Beams 17, 081004 (2014) BDSIM S (m) from IR 1 E (GeV / 10cm)

10. 10 As A Function of S Number of Particle Impacts S (m)

11. 11 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

12. 12 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

13. 13 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

14. 14 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

15. 15 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

16. 16Summary 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