The study of beam transport is of central importance to the design and
performance assessment of modern particle accelerators. In this work, we
benchmark two contemporary codes - DIMAD and BDSIM, the latter being a
relatively new tracking code built within the framework of GEANT4. We consider
both the 20 mrad and 2 mrad extraction lines of the International Linear
Collider (ILC) and we perform tracking studies of heavily disrupted
post-collision electron beams. We find that the two codes mostly give an
equivalent description of the beam transport.Comment: Contribution to the Tenth European Particle Accelerator Conference
  `"EPAC'06'', Edinburgh, United-Kingdom, 26-30 June 200

Appleby, R.

Bambade, P.

Dadoun, O.

Ferrari, A.

English

arXiv

The study of beam transport is of central importance to the design and performance assessment of modern particle accelerators. In this work, we benchmark two contemporary codes - DIMAD and BDSIM, the latter being a relatively new tracking code built within the framework of GEANT4. We consider both the 20 mrad and 2 mrad extraction lines of the International Linear Collider (ILC) and we perform tracking studies of heavily disrupted post-collision electron beams. We find that the two codes mostly give an equivalent description of the beam transport

Appleby, R

Bambade, P

Dadoun, O

Ferrari, A

CERN Document Server

arXiv:physics/0607165 v2   19 Jul 2006LAL/RT 06-06EUROTeV-Report-2006-038June 2006BENCHMARKING OF TRACKING CODES (BDSIM/DIMAD) USING THEILC EXTRACTION LINES ∗R. Appleby,The Cockcroft Institute and the University of Manchester,Oxford Road, Manchester, M13 9PL, EnglandP. Bambade, O. Dadoun,Laboratoire de l’Acce´le´rateur Line´aire,IN2P3-CNRS et Universite´ de Paris-Sud 11, BP 34, 91898 Orsay cedex, FranceA. Ferrari† ,Department of Nuclear and Particle Physics,Box 535, Uppsala University, 751 21 Uppsala, SwedenAbstractThe study of beam transport is of central importance tothe design and performance assessment of modern parti-cle accelerators. In this work, we benchmark two con-temporary codes - DIMAD and BDSIM, the latter beinga relatively new tracking code built within the frameworkof GEANT4. We consider both the 20 mrad and 2 mradextraction lines of the International Linear Collider (ILC)and we perform tracking studies of heavily disrupted post-collision electron beams. We find that the two codes mostlygive an equivalent description of the beam transport.INTRODUCTIONIn a high-energy e+e− linear collider such as ILC [1],the beams must be focused to extremely small spot sizesin order to achieve high charge densities and, in turn, toreach the desired luminosity. This leads to large angulardivergence and energy spread for the disrupted beams,as well as to the emission of beamstrahlung photons. Acareful design of the extraction lines must therefore beperformed to transport these outgoing beams from theinteraction point to their dumps with small losses. At ILC,two configurations are being studied for the crossing angleat the interaction point and, as a result, for the design ofthe post-collision lines. With a 2 mrad crossing angle, themain challenge is the extraction of the disrupted beam,which has to be achieved by sending the outgoing beamoff-center in the first large super-conducting defocusingquadrupole of the final focus beam line, as well as in thetwo nearby sextupoles [2]. On the other hand, with a∗Work supported by the Commission of the European Communi-ties under the 6th Framework Programme ”Structuring the EuropeanResearch Area”, contract number RIDS-011899.† ferrari@tsl.uu.se20 mrad crossing angle [3], one must deal with technicaldifficulties such as large crab-crossing corrections or theconstruction of compact super-conducting quadrupoles forthe incoming beam lines, as well as with the passage ofthe beams through the solenoid field with an angle. Forthe design of the ILC extraction lines, it is essential tohave a reliable simulation program for particle tracking. Inthis study, we present a comparison between two codes,DIMAD [4] and BDSIM [5], using the present versions ofthe ILC post-collision lines for benchmarking purposes, inboth large and small crossing angle cases.The DIMAD program specifically aims at studying thebehaviour of particles in beam lines, by computing theirtrajectories using the second order matrix formalism [6].The present version of the code ensures that the matrixtreatment is correct to all orders for energy deviations [4].This is important, as the ILC disrupted beams downstreamof the interaction point can have very large energy spreads.As for the BDSIM program [5], it uses the closed solu-tions in linear elements, whilst for higher-order elements,a GEANT4-like stepper integration method is used. Theprogram is written in GEANT4 [7] and provides a toolkitto simulate interactions of particles with the surroundingmatter once they have left the vacuum pipe. However, forthe purpose of this study, we only aim at comparing thetracking procedures in DIMAD and BDSIM.DIMAD AND BDSIM TRACKING IN THE20 MRAD EXTRACTION LINEFor this benchmarking study, we use the nominal beamparameters for ILC at 500 GeV, for which the beamtransport from the interaction point to the dump is almostloss-free (at least with the low-statistics input files that weuse). The particle distributions for the disrupted beams atthe interaction point were obtained with GUINEA-PIG [8]and then transported, with DIMAD or BDSIM, along theILC 20 mrad extraction line. The optics used for this studyconsists of a DFDF quadruplet, followed by two verticalchicanes for energy and polarization measurements and along field-free region that allows the beam to grow natu-rally, with two round collimators to reduce the maximumbeam size at the dump, see Figure 1.0.0 50. 100. 150. 200. 250. 300. 350. 400.s (m)δE/ p 0c = 0 .Table name = APERDisrupted beta functions and dispersion.SUN version 8.23/06 01/06/05  12.38.570.0500.1000.1500.2000.2500.3000.β1/2(m1/2 )0.00.010.020.030.040.050.060.070.080.090.10Dy(m)βx1 / 2 βy1 / 2 DyFigure 1: Betatron functions and vertical dispersion alongthe ILC extraction line with a 20 mrad crossing angle.At several locations of interest, we project the transversebeam distributions obtained with each program into binnedhistograms and we compare them quantitatively. An illus-tration of this procedure is shown in Figures 2 and 3 forthe transverse beam distributions obtained respectively atthe secondary focus point Mexfoc, located at s = 142.4 m(where βx and βy are very small, with a vertical dispersionof 2 cm) and at the dump. The open circles show the ratiobetween the number of events found by DIMAD or BDSIMin a given histogram bin and the error bars account for thelimited number of events per bin (very few events are foundin the tails, which explains the large error bars there). Thetransverse distributions of the disrupted beams were alsocomputed with DIMAD and BDSIM at several other loca-tions in the 20 mrad extraction line. Their comparison alsoshowed excellent agreement.DIMAD AND BDSIM TRACKING IN THE2 MRAD EXTRACTION LINEWhen the colliding beams cross with a small horizontalangle of 2 mrad, the outgoing disrupted beam passes off-axis through the bore of the final quadrupole QD0, both fi-nal sextupoles, but not the second-to-final quadrupole QF1.However, the outgoing beam sees the pocket field of thislatter magnet. Following this doublet, the beam is focusedwith a series of large bore quadrupoles. These are followedby a vertical energy clean-up chicane, diagnostic chicanesfor the purpose of energy spectrometry and polarimetry,and finally a long field-free region to allow the beam togrow to the dump, in the same way as in the 20 mradscheme. Note that, in the 2 mrad scheme, separate dumpsare used for the charged beam and for the beamstrahlungphotons.11010 210 310 410 5-30 -20 -10 0 10 20 30DIMAD BDSIMX at the 2nd focus point (mm)Events11010 210 310 410 5-10 -8 -6 -4 -2 0DIMAD BDSIMY at the 2nd focus point (mm)Events00.20.40.60.811.21.41.61.820 10 20 30 40 50 60Ratio = 1.00325 ± 0.0355439X bin numberDIMAD vs BDSIM00.20.40.60.811.21.41.61.820 10 20 30 40 50 60Ratio = 0.999845 ± 0.00177929Y bin numberDIMAD vs BDSIMFigure 2: Comparison of the transverse beam distributionsobtained with DIMAD (full circles) and BDSIM (full line)at the secondary focus point Mexfoc. Both upper plots aredistributed over 60 bins. The bottom plots show the ratio ofthe DIMAD and BDSIM distributions (see text for details).0500100015002000250030003500400045005000-8 -6 -4 -2 0 2 4 6 8DIMAD BDSIMX at the dump (cm)Events010002000300040005000600070008000-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4DIMAD BDSIMY at the dump (cm)Events0.50.60.70.80.911.11.21.31.41.50 10 20 30 40 50 60Ratio = 1.00092 ± 0.00755021X bin numberDIMAD vs BDSIM0.50.60.70.80.911.11.21.31.41.50 10 20 30 40 50 60Ratio = 1.00057 ± 0.00452743Y bin numberDIMAD vs BDSIMFigure 3: Same as Figure 2, obtained at the end of the20 mrad extraction line.The version of the linear optics used for this study is shownin Figure 4.0.0 100. 200. 300. 400. 500. 600. 700. 800.s (m)δ E/ p 0c = 0 .Table name = TWISSDisrupted beta functions for nominal energy.Windows NT 4.0 version 8.23dl 04/11/05  10.40.450.0500.1000.1500.2000.2500.3000.3500.4000.β1/2(m1/2 ) β x 1 / 2 β y1 / 20.0 200. 400. 600. 800.s (m)δ E/ p 0c = 0 .Table name = TWISSDispersion functionWin32 version 8.51/15 20/01/06  14.45.18-0.17-0.15-0.12-0.10-0.07-0.05-0.020.00.030.050.080.10D(m) Dx DyFigure 4: Betatron functions along the ILC 2 mrad post-collision line (top) and dispersion functions downstream ofthe final doublet of the incoming beam line (bottom).Following the BDSIM/DIMAD comparison in 20 mradscheme, we now simply describe the results obtained forthe 2 mrad case, using exactly the same beam. Figures 5to 7 show the results of the comparison at three locationsalong the 2 mrad extraction line. Figures 5 and 6 showthe comparison at Mexfoc1 (located just after the energyclean-up chicane) and at Mexfoc2 (the secondary focus ofthe polarimetry chicane), respectively. As for Figure 7, itshows the comparison at the beam dump.In these plots, we have projected the transverse beam dis-tributions obtained from the particle tracking into bins, andwe have then formed the ratio of the DIMAD prediction tothe BDSIM prediction. As in the previous section, the opencircles show the ratio, with the error bars accounting forthe limited number of events in a given bin. All diagramsshow a good agreement between DIMAD and BDSIM forthe ILC 2 mrad extraction line, except at the secondaryfocus of the polarimetry chicane (Mexfoc2), where slightdiscrepancies are visible. These may be due to differenttreatments of the high-order effects in the optical transportthrough non-linear elements.02505007501000125015001750200022502500-3 -2 -1 0 1 2 3X at MEXFOC1 (cm)Events010002000300040005000600070008000-0.25 -0.2 -0.15 -0.1 -0.05 0 0.05Y at MEXFOC1 (cm)Events0.50.60.70.80.911.11.21.31.41.50 10 20 30 40 50 60Ratio = 0.97325 ± 0.083719X bin numberDIMAD vs BDSIM0.50.60.70.80.911.11.21.31.41.50 10 20 30 40 50 60Ratio = 1.00053 ± 0.0147374Y bin numberDIMAD vs BDSIMFigure 5: Comparison of the transverse beam distributionsobtained with DIMAD (full circles) and BDSIM (full line)at Mexfoc1. Both upper plots are distributed over 60 bins.The bottom plots show the ratio of the DIMAD and BDSIMdistributions.11010 210 310 410 5-1 -0.8 -0.6 -0.4 -0.2 0 0.2X at MEXFOC2 (cm)Events11010 210 310 410 5-0.3 -0.25 -0.2 -0.15 -0.1 -0.05 0Y at MEXFOC2 (cm)Events0.50.60.70.80.911.11.21.31.41.50 10 20 30 40 50 60Ratio = 1.0325 ± 0.127285X bin numberDIMAD vs BDSIM0.50.60.70.80.911.11.21.31.41.50 10 20 30 40 50 60Ratio = 1.00255 ± 0.0359225Y bin numberDIMAD vs BDSIMFigure 6: Same as Figure 5, obtained at Mexfoc2.050010001500200025003000-8 -6 -4 -2 0 2 4 6 8X at the dump (cm)Events010002000300040005000600070008000-0.6 -0.4 -0.2 0 0.2 0.4 0.6Y at the dump (cm)Events0.50.60.70.80.911.11.21.31.41.50 10 20 30 40 50 60Ratio = 0.990938 ± 0.0412658X bin numberDIMAD vs BDSIM0.50.60.70.80.911.11.21.31.41.50 10 20 30 40 50 60Ratio = 0.999484 ± 0.046563Y bin numberDIMAD vs BDSIMFigure 7: Same as Figure 5, obtained at the dump.CONCLUSIONIn this paper, we performed a detailed benchmarkingstudy of two particle tracking codes, DIMAD and BDSIM.For this purpose, we have considered the ILC extractionlines with a crossing angle of 2 mrad or 20 mrad and,in each of these two configurations, we have performedtracking studies of disrupted post-collision electron beams.Here, only the nominal luminosity case of the 500 GeVmachine was studied. We find that both programs give anequivalent description of the beam transport in all parts ofthe post-collision lines, except at the secondary focus forthe 2 mrad design, where a small difference is visible.REFERENCES[1] http://www.interactions.org/linearcollider/[2] Y. Nosochkov et al., ”Optics of the extraction line forthe 2 mrad crossing angle”, EuroTeV-Report-2006-001 andSLAC-PUB 11613.[3] R. Arnold, K. Moffeit, Y. Nosochkov, W. Oliver, A. Seryi,E. Torrence and M. Woods, “Design of ILC extraction linefor 20 mrad crossing angle”, Proceedings of PAC 2005,Knoxville, USA.[4] http://www.slac.stanford.edu/accel/ilc/codes/dimad[5] http://flc.pp.rhul.ac.uk/bdsim.html[6] K.L. Brown, D.C. Carey, Ch. Iselin and F. Rothacker,“TRANSPORT, a computer program for designing chargedparticle beam transport systems”, SLAC 91 (1973 Rev.),NAL 91 and CERN 80-04.[7] GEANT4 Collaboration (S. Agostinelli et al), ”GEANT4:a simulation toolkit”, Nucl. Instr. and Meth. NIM A 506(2003), 250-303.[8] D. Schulte, TESLA-97-08 (1996).

Benchmarking of Tracking Codes (BDSIM/DIMAD) using the ILC Extraction Lines

Contribution to the Tenth European Particle Accelerator Conference "EPAC'06'', Edinburgh, United-Kingdom, 26-30 June 2006 - Groupe ILCThe study of beam transport is of central importance to the design and performance assessment of modern particle accelerators. In this work, we benchmark two contemporary codes - DIMAD and BDSIM, the latter being a relatively new tracking code built within the framework of GEANT4. We consider both the 20 mrad and 2 mrad extraction lines of the International Linear Collider (ILC) and we perform tracking studies of heavily disrupted post-collision electron beams. We find that the two codes mostly give an equivalent description of the beam transport

Ferrari, Anthony

HAL-IN2P3

The study of beam transport is of central importance to the design and performance assessment of modern particle accelerators. In this work, we benchmark two contemporary codes - DIMAD and BDSIM, the latter being a relatively new tracking code built within the framework of GEANT4. We consider both the 20 mrad and 2 mrad extraction lines of the International Linear Collider (ILC) and we perform tracking studies of heavily disrupted postcollision electron beams. We find that the two codes mostly give an equivalent description of the beam transport

Benchmarking of Tracking Codes (BDSIM/DIMAD) using the ILC Extraction Lines

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