ILC collimation using Beam Delivery Simulation (BDSIM)
S. T. Boogert, L. Nevay, J. Snuverink, H. Garcia Morales
ALCWS KEK, Tsukuba, Japan
20th April 2015
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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
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• 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 radiationo hadronic processes too
• Library of generic geometry used
BDSIM
Beam line example (ATF2)
Component example (LHC dipole)
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• CLICo Similar use case as ILCo Muons
• LHCo Ring upgrades, turn controlo Losses in collimation system,
cold losses
BDSIM applications
L. Nevay; https://indico.cern.ch/event/326148/session/30/contribution/91
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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)
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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
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• BDSIMo Generic machine builder
• MAD8/MADXo Run MAD8/MADX generate
twiss output or saveline outputo 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
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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)
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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
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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
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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
IPLWC POLC BCOL
ECOL
DUMP
LWC
POLC
BCOL
NB : Vertical scale x 100
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• ILC2015a EBSY parameters
Phase space
Parameter Value
Energy 250 GeV
Emit_x 0.188x10-10 m
Emit_y 0.696x10-13 m
Bet_x 71.482 m
Bet_y 39.604 m
Alf_x -1.564
Alf_y 1.283
Sigma_E 0.2 %
Parameter Value
Halo_x 6 Sigma_x
HaloSigma_x 1 Sigma_x
Halo_y 40 Sigma_y
HaloSigma_y 1 Sigma_y
Nominal EBSY phase space
Horizontal collimator phase space
NB : Need proper halo phase space
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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 sureabout this
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First results : SR
• Blue: primary beam particles• Green: SR photons
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First results : SR
• Blue: primary beam particles• Green: SR photons
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First results : SR loss map
• Primaries (5000)• Nominal beam
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Collimation system losses
• Primaries (5000)• X : 6 sigma halo phase space, Y : Nominal• Collimators and absorbers set at 6 sigma
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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
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Higher statistics
• Early development tests with high statistics (very large emittance)― Order 1 million primaries (4 hours on 250 node farm, )
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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
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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
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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
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References
• ILC collimation ― https://agenda.linearcollider.org/event/6389/session/14/contribution/32
• ILC decks― https://bitbucket.org/whitegr/ilc-lattices
• BDSIM― https://bitbucket.org/stewartboogert/bdsim― https://twiki.ph.rhul.ac.uk/twiki/bin/view/PP/JAI/BdSim
• Application talks― L. Nevay; https://indico.cern.ch/event/326148/session/30/contribution/
91― F. Belgin; https://indico.cern.ch/event/336335/session/0/contribution/117
• ATF2 halo measurement― https://indico.cern.ch
/event/336335/session/0/contribution/109/material/slides/0.pdf