Abramov, A

Bodenstein, RM

Boogert, ST

Burrows, P

Nevay, LJ

Schulte, D

Tomás, R

Burrows, Philip

Oxford University Research Archive

INVESTIGATION OF CLIC 380 GeV POST-COLLISION LINER.M. Bodenstein∗†1, P.N. Burrows1, JAI at University of Oxford, Oxford, UKL.J. Nevay1, A. Abramov1, S.T. Boogert, JAI at Royal Holloway University of London, Egham, UKD. Schulte, R. Tomás, CERN, Meyrin, Switzerland1also at CERN, Meyrin, SwitzerlandAbstractIt has been proposed that the Compact Linear Collider(CLIC) be commissioned in stages, starting with a lower-energy, 380 GeV version for the first stage, and concludingwith a 3 TeV version for the final stage. In the Conceptual De-sign Report (CDR) [1] published in 2012, the post-collisionline is described for the 3 TeV and 500 GeV stages. How-ever, the post-collision line for the 380 GeV design was notinvestigated. This work will describe the simulation studiesperformed in BDSIM [2] for the 380 GeV post-collision line.GOALSThe goal of any post-collision line study is to make surethat both collided and uncollided beams can be safely guidedto a dump. These beamlines must be able to account forlarge energy spreads, wrong-charge particles, and minimizedeposition on beamline components.This work was performed for the CLIC Project Imple-mentation Plan [3], which was presented to the EuropeanStrategy Update in December of 2018. For this work, thegoal was to confirm that the post-collision line design pre-viously investigated for the 3 TeV phase of CLIC [4–6] willwork for the initial 380 GeV phase. It is important to notethat the design of the dump itself is not included in this work.PREVIOUS WORKPrevious studies of the CLIC post-collision line (PCL)focused almost entirely on the 3 TeV version of the machine.Mentions of lower-energy versions were briefly discussed,but no in-depth, detailed studies were performed. Severalversions of the 3 TeV post-collision line have been made[4–6], and while overall the layouts are similar, they differin various details.For the present work, the authors generally endeavoredto use the same design as that described in the CDR [1].Occasionally, design aspects from other sources were usedinstead. Additionally, minor changes were made when it im-proved the overall design, or when designs were inconsistentwith each other.OVERVIEW OF PRESENT DESIGNThe majority of the overall layout remains the same asthose found in [4–6]. The distances remain the same fromthe interaction point (IP), as well as between the magnets andintermediate dump (ID). The authors opted to use the 50 m∗ ryan.bodenstein@physics.ox.ac.uk† Now at SCK-CENversion of the final drift to the dump, as in [4]. All of thegeometries in this study were created using a python-basedBoolean geometry toolkit, pyg4ometry [7, 8].One change involved the first set of window-frame mag-nets. Described in the CDR and elsewhere, these magnetswere to have lengths of 0.5 m and 3.5 m, respectively. How-ever, this is inconsistent with the designs made by the magnetgroup [9]. Here, each magnet was 2 m in length. Both ver-sions were tested in BDSIM, and the results were identicalfor both 3 TeV and 380 GeV. The authors opted to use the2 m versions, as this is what the magnet group designed.Minor changes were also required with the carbon-basedmasks in between each window-frame magnet. The aperturesizes of these masks were not consistently reported, so theauthors chose for this initial study to match the aperturesize to the beampipe size at each location. This may notbe optimal, but for the purposes of this initial study it issufficient.All of the beampipes upstream of the intermediate dumpare elliptical cones which gradually increase in size from theIP to the ID. Most of this growth occurs in the y-plane, asthe beam is highly divergent in this plane after the IP. Theseshapes are consistent with previous designs.The window-frame magnets are also consistent with pre-vious design studies. A new beampipe shape was added tothe BDSIM functionality to take into account the ellipticalbeampipes inside of these magnets.The intermediate dump remains geometrically the sameas previous designs. The geometry allows for wrong-chargeparticles to be deposited into the upper part of the ID, lower-energy particles to be deposited in the lower part of the ID,and particles close to nominal energy to pass through theaperture. The geometry for the intermediate dump is shownin Fig. 1.The beampipes downstream of the ID match previous de-scriptions as well. At the end closest to the ID, the beampipehas a two-half-ellipse design, which can be shown in Fig. 2.As the beampipe continues past the C-shaped dipoles to themain dump (MD), this shape gradually changes to a racetrackshape just before the main dump. The C-shaped magnetsallow for this two-half-ellipse beampipe shape. The maindump geometry is based on that described [10].Figure 3 shows the overall 3D layout of the PCL.BDSIM SIMULATIONSTo begin the simulation process, the settings are testedinteractively in BDSIM. This is done with a fewer numberof particles (approximately 1000) in order to make sure that10th Int. Partile Accelerator Conf. IPAC2019, Melbourne, Australia JACoW PublishingISBN: 978-3-95450-208-0 doi:10.18429/JACoW-IPAC2019-MOPMP038MOPMP038528ContentfromthisworkmaybeusedunderthetermsoftheCCBY3.0licence(©2019).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOIMC1: Circular and Linear CollidersA03 Linear CollidersFigure 1: Side-angle view of the intermediate dump.Figure 2: Two-half-ellipse geometry.the general behavior of the particles is consistent with whatis expected given the beamline optics.Once the interactive simulations are checked, the simu-lations are then performed using the batch system. Here,approximately 1,000,000 particles are simulated. For the ini-tial beam distributions, we used data provided by the beam-beam interactions group, which was found using GUINEA-PIG [11]. Since BDSIM simulations can produce largeamounts of data, certain cuts must be performed to speedup the process. For our simulations, any particle, includ-ing secondaries, which had an energy lower than 20 MeVwere excluded from analysis since they are unlikely to sig-nificantly contribute to the deposition along the beamline.Additionally, any particles that do not travel at least 1 cmwere also cut, for the same reasons.The primary analysis is actually performed during thesimulation itself with ROOT. This requires knowing whatdata is needed, and at which locations. This is done to limitthe amount of data which is copied back, since it can easilybe over 1 terabyte. Instead, only the histogram data providedby the ROOT analysis is copied back for further analysis.To perform this analysis on the histogram data, the pybd-sim utilities are used. With these, detailed particle and powerdeposition plots can be created.RESULTSFor the Project Implementation Plan (PIP) study, only themost important aspects were investigated. The focus wason reproducing previous 3 TeV results to check for consis-tency, and then to study the same setup with reduced magnetstrengths at 380 GeV.We first tested that the 3 TeV setup would behave similarlyto previous studies. Some of the results are shown in Table1 for both the collided (C) and uncollided (U) 3 TeV beams.The power deposited in the intermediate dump, along thefinal drift, and in the main dump is within expectations, andthere were no unexpected "hot spots" along the beamline.The maximum power deposited into the main dump is 13.6MW, which is below the designed 14 MW capability.Once we were confident in our 3 TeV simulations, we thenscaled the dipole magnet strengths from 0.8 T to 0.1 T for the380 GeV case (to achieve the same 0.64 mrad kick per dipoleas in the 3 TeV case). Some of these results are also shown inTable 1. These results are as expected from previous studies.Table 1: Power Deposited (MW) in Key PCL Elements forboth Uncollided (U) and Collided (C) BeamsInt. Dump Final Drift Main Dump3 TeV U 2.10×10−4 1.97 × 10−2 13.63 TeV C 3.67×10−2 2.96 × 10−2 10.2380 GeV U 5.19×10−5 4.08 × 10−3 2.91380 GeV C 7.77×10−5 4.23 × 10−3 2.70What was unknown for the 380 GeV design is whetherthere would be hot spots or other unexpected behavior bythe beam as it passed through the PCL designed for the3 TeV version of CLIC. Figures 4 and 5 show the depositionalong the post-collision line for both the uncollided andcollided 190 GeV beams, respectively. There appear to beno unexpected "hot spots" or other anomalies which impactthe energy deposition. Additionally, the majority of the beamis deposited at or below the center of the main dump, whichis as previously designed.CONCLUSIONThese studies show that the basic designs previously de-scribed for the 3 TeV CLIC machine should be adequate forthe 380 GeV version. It should be possible to use the samedesign with the magnets scaled from 0.8 T to 0.1 T for the380 GeV case. Further studies can be performed to improveupon this.10th Int. Partile Accelerator Conf. IPAC2019, Melbourne, Australia JACoW PublishingISBN: 978-3-95450-208-0 doi:10.18429/JACoW-IPAC2019-MOPMP038MC1: Circular and Linear CollidersA03 Linear CollidersMOPMP038529ContentfromthisworkmaybeusedunderthetermsoftheCCBY3.0licence(©2019).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOIFigure 3: Graphical output of BDSIM showing the post-collision line design.Figure 4: Heat map of deposition for uncollided 190 GeV electron beam.Figure 5: Heat map of deposition for collided 190 GeV electron beam.FURTHER STUDIESTo improve the design of both the 3 TeV and 380 GeVPCL, several items should be investigated further. For bothcases, the apertures for the carbon-based masks should beoptimized to further reduce deposition on the window-framemagnets. Also, including studies of wrong-charge particles,beamstrahlung, incoherent pairs, and muons would be im-portant for completeness. Opportunities for instrumentationshould also be investigated.For the 380 GeV machine, it may be feasible to removeseveral of the dipoles and scale the strengths accordingly toachieve the same optics and results. This would mean scalingthe magnets below 0.8 T, but higher than 0.1 T, aiming forthe same total bend angles in each section of the PCL. Inthe place of the removed dipoles, drift space could remain.When the higher-energy machines are commissioned, thedipoles can simply be added into the drift space. This wouldbe a simple study to perform, and could potentially save costfor the lower-energy designs.10th Int. Partile Accelerator Conf. IPAC2019, Melbourne, Australia JACoW PublishingISBN: 978-3-95450-208-0 doi:10.18429/JACoW-IPAC2019-MOPMP038MOPMP038530ContentfromthisworkmaybeusedunderthetermsoftheCCBY3.0licence(©2019).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOIMC1: Circular and Linear CollidersA03 Linear CollidersREFERENCES[1] M. Aicheler et al., “A Multi-TeV Linear Collider Based onCLIC Technology: CLIC Conceptual Design Report”, doi:10.5170/CERN-2012-007[2] L. Nevay et al., “BDSIM: An Accelerator Tracking Code withParticle-Matter Interactions”, 2018, https://arxiv.org/abs/1808.10745[3] M. Aicheler et al., “The Compact Linear Collider(CLIC) - Project Implementation Plan,” doi:10.23731/CYRM-2018-004[4] A. Ferrari, V. Ziemann, R. B. Appleby, and M. D. Salt,“Conceptual design of a beam line for post-collision extrac-tion and diagnostics at the multi-TeV Compact Linear Col-lider,” Phys. Rev. ST Accel. Beams, vol. 12, p. 021001, 2009.doi:10.1103/PhysRevSTAB.12.021001[5] D. Angal-Kalinin, R. Appleby, J. Jones, A. Scarfe, and S. Ty-gier, “ATF2 Tests and CLIC IR Study,” EuCARD-REP-2013-012 http://cds.cern.ch/record/1710304[6] E. Gschwendtner, “CLIC Post-Collision Line and Dump”,2010, https://indico.cern.ch/event/110479/contributions/43439/[7] pyg4ometry, https://bitbucket.org/jairhul/pyg4ometry/src/master/[8] S. T. Boogert et al., “Pyg4ometry : A Tool to Create Ge-ometries for Geant4, BDSIM, G4Beamline and FLUKA forParticle Loss and Energy Deposit Studies”, presented at the10th Int. Particle Accelerator Conf. (IPAC’19), Melbourne,Australia, May 2019, paper WEPTS054, this conference.[9] A. Vorozhtsov, “Preliminary design of CLIC main beamnormal conducting magnets required for the post collisionline”, September 2010, CERN-ATS-Note-2011-024-TECH,https://cds.cern.ch/record/1344794[10] A. Mereghetti, C. Maglioni, and V. Vlachoudis, “Fluka andthermo-mechanical studies for the CLIC main dump”, March,2011, CERN-OPEN-2011-030, https://cds.cern.ch/record/1355402[11] CLIC Beam-beam Interactions, doi:https://doi.org/10.5281/zenodo.1467017, http://clic-beam-beam.web.cern.ch/clic-beam-beam/10th Int. Partile Accelerator Conf. IPAC2019, Melbourne, Australia JACoW PublishingISBN: 978-3-95450-208-0 doi:10.18429/JACoW-IPAC2019-MOPMP038MC1: Circular and Linear CollidersA03 Linear CollidersMOPMP038531ContentfromthisworkmaybeusedunderthetermsoftheCCBY3.0licence(©2019).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOI

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Investigation of CLIC 380 GeV post-collision line

Investigation of CLIC 380 GeV post-collision line

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