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