ILC collimation using Beam Delivery Simulation (BDSIM) S. T. Boogert, L. Nevay, J. Snuverink, H. Garcia Morales ALCWS KEK, Tsukuba, Japan 20 th April 2015

2 Introduction BDSIM ― Introduction to BDSIM ― Underlying principles ― Applications to other machines ― Practical conversion of MAD8 deck ILC model status ― Application areas ― Visualisation of conversion ― Comparison of linear optics Collimation system setting Synchrotron radiation Collimation losses Muon production Summary

3 Tracking code that uses Geant4 Used to simulate energy deposition and detector backgrounds Particles tracked through vacuum using normal tracking routines Geant4 provides physics processes for interaction with machine Full showers of secondaries created by Geant4 processes Secondaries tracked throughout the accelerator Ability to simulate o synchrotron radiation o hadronic processes too Library of generic geometry used BDSIM Beam line example (ATF2) Component example (LHC dipole)

4 CLIC o Similar use case as ILC o Muons LHC o Ring upgrades, turn control o Losses in collimation system, cold losses BDSIM applications L. Nevay;

5 BDSIM development Long (but slow) ~decade development at RHUL ― Started by Prof Grahame Blair ― Used primarily for ILC and CLIC ― Recently adapted for LHC ― Current development team (4-5 people, mainly LHC) Substantial improvements to code ― Much less code ― Much more stable ― Multiple auxiliary python libraries to help user pymad8 : MAD8 helper code pymadx : MADX helper code robdsim : analysis of root files pybdsim : conversion of deck, plotting etc ― Machine lattice definition to working simulation ~minutes ― Easy to use! (all of this presentation was generated over weekend by lazy academic)

6 Areas to apply BDSIM in ILC Compton diagnostics ― Laser wire scanners (background sets laser power, fibre delivery, subterranean laser room) ― Polarimeters (reintegration of polarimeter chicane with LW, laser power?) Collimator system ― Protection collimation system ― Betatron collimation (muon generation and muon spoilers) ― Energy collimation IR region SR ― Hits in IR region Downstream diagnostics ― Energy spectrometer ― Polarimeter

7 BDSIM o Generic machine builder MAD8/MADX o Run MAD8/MADX generate twiss output or saveline output o Slightly different for LHC/MADX Conversion from MAD to BDSIM MAD8 output (twiss.tape/saveline+structure.tape+envelope.tape) Components Sequence Collimators Apertures Beam parameters Python modify Collimators Apertures Beam phase space Python generates BDSIM input Components Sequences Beam Options BDSIM output root files Histograms of losses Complete information of particles passing a surface

8 Apertures Extract APER values from MAD8 ― Compare with beam sizes ― Seems to be quite a difference compared with TDR ― Use apertures from MAD8 deck to define beam pipe radius ― Transitions between different radii not treated correctly now (eg. tapers)

9 IR Apertures test Track nominal beam through IR ― No physics processes enabled ― 5000k particles ― Sorry forgot the sextupoles! Final doublet IP NB expanded vertical scale

10 Collimators Extract X and Y SIZES of RCOL and ECOL from MAD8 file ― Set values from optics as calculated by MAD8 ― Existing settings are definitely not correct ― Set 6 Sigma_x and 40 Sigma_y for tests

11 Visualisation of conversion OpenGL used to view the BDSIM geometry ― Also primaries and secondary particles (not shown in figures) ― Dipoles : blue, Quads : red, Collimators : green ― Laserwire chicane (LWC), Polarimeter chicane (POLC), Betatron collimation (BCOL), Energy collimation (ECOL) IP LWCPOLCBCOL ECOL DUMP LWC POLC BCOL NB : Vertical scale x 100

12 ILC2015a EBSY parameters Phase space ParameterValue Energy250 GeV Emit_x0.188x m Emit_y0.696x m Bet_x m Bet_y m Alf_x Alf_y1.283 Sigma_E0.2 % ParameterValue Halo_x6 Sigma_x HaloSigma_x1 Sigma_x Halo_y40 Sigma_y HaloSigma_y1 Sigma_y Nominal EBSY phase space Horizontal collimator phase space NB : Need proper halo phase space

13 Linear optics comparison Check optics before generation of secondary particles TDR EBSY start twiss and emittance ― Opened all collimators (betatron, energy, protection) ― Track 5k particles with all secondary generation off Not sure about this

14 First results : SR Blue: primary beam particles Green: SR photons

15 First results : SR Blue: primary beam particles Green: SR photons

16 First results : SR loss map Primaries (5000) Nominal beam

17 Collimation system losses Primaries (5000) X : 6 sigma halo phase space, Y : Nominal Collimators and absorbers set at 6 sigma

18 First results : Muon production Sorry didn’t get to this in time ― Once collimator apertures are defined need to enable the G4 processes Gamma+gamma Pion production Positron annihilation Also check re-weighting of particle physics processes (work on going at CLIC/CERN) ― Working fine for CLIC see slide 4

19 Higher statistics Early development tests with high statistics (very large emittance) ― Order 1 million primaries (4 hours on 250 node farm, )

20 BDSIM Improvements required More realistic geometry ― Parametrised multipoles (almost complete) ― Parametrised tapered collimators (almost complete) Careful checking of non-linear optics ― Comparison with PTC tracking of MADX ― Careful checking of sextupole and high order magnets Efficient generation of halo ― Need correct correlations but only at large amplitude Identification of photons/muons with primaries Check implementation of muon spoilers

21 Next steps for ILC Perform same study as G. White presented in LCWS2014 Belgrade Optimise SP1,2,3,4,5, SPEX Scans of absorbers (ABXX)? Calculate scaled (per Bunch-crossing or train) ― Losses in collimation system ― Muons (flux, direction, spectrum for IR) ― Losses for LW and Polarimeter chicanes ― Anything else??? Phase advances between collimators and final double and IP are not optimal ― Follow changes in the optics quickly using BDSIM Use upgraded geometry

22 Summary Automatic conversion of MAD8 decks to BDSIM complete ― Collimators ― Apertures ― Linear optics Few BDSIM improvements still required ― Non-linear optics (tests) ― Geometry ― Halo phase space Lots of work required for complete simulation of BDS collimation system, fundamentals are there ― More complete results by summer 2015 ― Hopefully to inform Japan specific CFS decisions

23 References ILC collimation ― ILC decks ― BDSIM ― ― Application talks ― L. Nevay; L. Nevay; ― F. Belgin; F. Belgin; ATF2 halo measurement ― slides/0.pdf slides/0.pdf