Agapov, Ilya

Blair, Grahame A $uRoyal Holloway, University of London, Surrey

Carter, John

Deacon, Lawrence

Drozhdin, Alexandr I

Mokhov, Nikolai V

Nosochkov, Yuri

Seryi, Andrei

CERN Document Server

SIMULATION OF THE ILC COLLIMATION SYSTEM USING BDSIM,MARS15 AND STRUCT∗J. Carter, I. Agapov, G. A. Blair, L. Deacon, (JAI/RHUL, UK),A. I. Drozhdin, N. V. Mokhov (Fermilab, US),Y. Nosochkov, A. Seryi (SLAC, US)AbstractThe simulation codes BDSIM [1], MARS15 [2] andSTRUCT [3] are used to simulate in detail the collimationsection of the International Linear Collider (ILC) [4]. Acomparative study of the collimation system performancefor the 250 GeV machine is conducted, and the key radia-tion loads are calculated. Results for the latest ILC designsare presented together with their implications for future de-sign iterations.INTRODUCTIONThe ILC is expected to run with 250 − 500 GeV e+/e-beams with approximately 20 MW power. The Beam De-livery System (BDS), see Fig. 1, is a key part of the ac-celerator which should provide precise bunch collisions ona nanometer scale. Two detectors are now under design -with 2 and 20 mrad crossing angle. The BDS layouts forthese detectors will be referred to as 2 and 20 mrad systemsrespectively.Figure 1: The layout of the ILC beam delivery system.Interactions of the beam halo with detector componentsand the Synchrotron Radiation (SR) it produces can causea large amount of background in the Interaction Region(IR). The collimation system [5] is designed to scrape thehalo away. Due to high beam energy and power the col-limation system becomes a critical issue: the collimatorscan be damaged and the secondary particles produced inbeam-collimator interactions can themselves cause notice-able backgrounds. The extraction lines also have collima-tion systems serving to protect the magnets from radiationloads. These collimation systems are usually referred to as“downstream” and the former as “upstream”.The upstream collimation system is two-stage. In the β-collimation section the halo particles with large transverse∗Work supported in part by the British Council Alliance programme,the PPARC LC-ABD Collaboration, and by the Commission of EuropeanCommunities under the 6th Framework Programme Structuring the Euro-pean Research Area, contract number RIDS-011899deviation interact with thin spoilers and then are lost in theenergy collimation section along with off-momentum par-ticles.Figure 2: Sketch of ILC collimation system.To evaluate the performance of the collimation systemsimulations of power loads on key elements and the sec-ondary particles reaching the detector were performed. Toassure reliablility the simulations were performed with sev-eral codes:• BDSIM v0.2 [1] - a Geant4 based extension toolkit forbeam line simulations, combining fast tracking algo-rithms in accelerator components with the full showerproduction capabilities of Geant4.• MARS15 [2] - a set of Monte Carlo programs fordetailed simulations of electromagnetic and hadroniccascades in arbitrary 3-D geometrical configurationssuch as the ILC BDS.• STRUCT [3]- a Fortran based program to perform par-ticle tracking and interactions with material of colli-mators in synchrotrons and beam lines.THE UPSTREAM COLLIMATIONSYSTEMThe simulation of the collimation system in the up-stream beam delivery optics has been performed by track-ing “1/R2” (i.e. falling off as 1/R2 in phase space) beamhalo as in Fig. 3. For normalisation purposes this has beenassumed to constitute 10−3 of the main beam.For both upstream and downstream simulations withBDSIM, secondary particle production via standard elec-tromagnetic processes have been computed with lowerFigure 3: Top left: initial beam halo phase space. Top right:beam halo phase space at the IP. Bottom left: photon spatialdistribution at the IP. Bottom right: halo electron spatialdistribution at the IP.limit tracking thresholds set to 10 keV for both charged andneutral particles. Results for the normalised power lossesin the 20 mrad BDS as a result of running beam halo inBDSIM are presented in Fig. 4. All losses from beam haloare shown to within tolerable limits and the all halo-relatedparticles pass through the vertex detector aperture.carter, Mon Jun 12 13:26:17 BST 2006 BDSIM input file : ../0-100/gmad_file/ebds1.gm0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200Z [m]0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200Power [W/m]-1010-910-810-710-610-510-410-310-210-110110210310Power Loss from Halo Particles in the 20mrad Beam Delivery SystemFigure 4: Normalised power losses due to beam halo andcorresponding SR along the 20 mrad BDS. Given as a func-tion of distance from the linac.Beam envelopes for beam halo and corresponding SRcan be used to give lower limits on the aperture size of allthe elements in the BDS. Results without tail folding oc-tupoles are given in Fig. 5. Using these octupoles causesthe envelope of the halo to increase.Figure 5: Beam envelope of the halo (shaded region) andthe SR (solid line) in the 20 mrad BDS. Horizontal apertureof elements is also plotted (dashed line).EXTRACTION LINESThe extraction lines guide the beam and the beam-strahlung from the IR to the beam dumps. The post-collision beams are disrupted and the collimation systemhere serves to protect the magnets from the radiation loads.The downstream collimation and power losses have beencalculated using high statistics for 250 GeV “Nominal”beam [6] with 0 and 200 nm vertical offset (see Fig. 6and 7). Comparisons with simulations without SR tracking[7] show that In both the 2 and 20 mrad extraction lines thepower curves are dominated by the SR losses. Distributionsfor SR and the core beam in the 2 mrad design have beenproduced at the entry point to key magnets using STRUCT(see Fig. 8).carter, Tue Jun 13 15:33:18 BST 2006 BDSIM input file : 20mrad.gmad0 50 100 150 200 250 300Distance from IP [m]0 50 100 150 200 250 300Power [W/m]-710-610-510-410-310-210-110110210250 GeV Nominal, 0nm Offset.250 GeV Nominal, 200nm Offset.Power Losses in the 20mrad Extraction LineFigure 6: Normalised power losses along the 20 mrad ex-traction line from disrupted beam and SR. Total integratedpower of 1.68 W for 0 nm and 1.66 w for 200 nm.Certain key magnets in the 2 mrad extraction line willuse superconducting technology which will set strict lim-its on any beam power incident upon them in terms ofavoiding quenching. The closest quadrupole to the 2mradcarter, Mon Jun 19 12:19:55 BST 2006 BDSIM input file : edl.gmad0 100 200 300 400 500 600Distance from IP [m]0 100 200 300 400 500 600Power [W/m]-210-110110210310410Power Losses in the 2mrad Extraction LineFigure 7: Normalised power losses along the 2 mrad ex-traction line for 250 GeV nominal disrupted beam with novertical offset and SR. Total integrated power of 45.8 kW.Figure 8: Beam distribution calculated with STRUCT.IR, QD0, is one such magnet and detailed studies havebeen conducted in order to fully predict the localised en-ergy load within its NbTi coils. Radiative Bhabhas gener-ated as a result of beam-beam interactions in the detectorregion provide the largest contribution to this power de-position. These particles, generated using GUINEA-PIG[8], have been tracked in BDSIM and by scoring QD0 intoapproximately 300,000 volumes comprehensive power de-position maps have been produced (see Fig. 9). Magnetdesigners of the similar superconducting quadrupoles forthe Large Hadron Collider (LHC) have set a maximumlocalised power deposition of 1.5 mW/g and due to theharsh conditions as a result of the close proximity to theIR, this value has been lowered to 0.5 mW/g for QD0 [9].Fig. 9 shows that for the 250 GeV nominal machine param-eters QD0 suffers a maximum localised power depositionof 1.8 mW/g in the NbTi coils. Simulations with a pre-showering Tungsten liner can reduce the power depositionlevels to below the set threshold for most of the suggestedmachine parameter sets, but further studies must be carriedout in order to fully evaluate the effects on normal beamtransport when using this liner.Figure 9: Power deposited into scored rings of supercon-ducting QD0 in the 2mrad extraction line from RadiativeBhabhas generated in the 250 GeV Nominal machine. Left:power into the aluminium beam pipe. Right: first 0.5 cmof the NbTi coils.CONCLUSIONSBy simulating the ILC collimation system performancewith different simulation tools and performing benchmark-ing it was possible to analyse the radiation environment inthe beam delivery system with a higher degree of confi-dence. Both STRUCT and BDSIM codes give similar re-sults. The performance of the upstream collimation sys-tem and the 20 mrad extraction line is found satisfactorywhereas the radiation loads on the 2 mrad extraction linerequire further optimization.REFERENCES[1] I. Agapov et al., The BDSIM Toolkit, 2006, EUROTeV-Report-2006-014 (In Review)[2] N.V. Mokhov, K.K. Gudima, C.C. James et al, Recent En-hancements to the MARS15 Code ,Fermilab-Conf-04/053,New MARS15 of 2004, ICRS-10 paper[3] A. Drozhdin and N. Mokhov, The STUCT Program User’sReference Manual, 2005, http://www-ap.fnal.gov/˜drozhdin[4] ILC Baseline Configuration Document Wiki web area,http://www.linearcollider.org/wiki/.doku.php[5] P. Tenenbaum, et al., Overview of collimation in the NextLinear Collider, Jun 2001, SLAC-PUB-8934[6] T. Raubenheimer, Suggested ILC Beam Pa-rameter Range, Feb 2005, http://www-project.slac.stanford.edu/ilc/acceldev/beamparameters.html[7] J. Carter, Extraction Line Power Losses for 2, 14, and 20mrad designs, presented at LCWS06,http://indico.cern.ch/materialDisplay.py?contribId=222&amp;sessionId=11&amp;materialId=slides&amp;confId=568[8] D. Schulte, Ph. D. Thesis, University of Hamburg, 1996.TESLA-97-08[9] T. Maruyama and L. Keller, Energy Deposition in Supercon-ducting QD0 from Radiative Bhabha’s for 2mrad Crossing,Presented at SLAC BDS Meeting July 2005

Simulation of the ILC Collimation System using BDSIM, MARS15 and STRUCT

Simulation of the ILC Collimation System using BDSIM, MARS15 and STRUCT

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