ilc collimation using beam delivery simulation (bdsim) s. t. boogert, l. nevay, j. snuverink, h....

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