Detailed STRUCT simulations are performed on beam loss rates in the vicinity of the BTeV detector in the Tevatron CO interaction region due to beam-gas nuclear elastic interactions and out-scattering from the collimation system. Corresponding showers induced in the machine components and background rates in BTeV are modeled with the MARS14 code. It is shown that the combination of a steel collimator and concrete shielding wall located in front of the detector can reduce the accelerator-related background rates in the detector by an order of magnitude

Drozhdin, Alexandr I.

Mokhov, Nikolai V.

UNT (University of North Texas) Digital Library

Fermilab FERMILAB-Conf-04/099-AD July 2004MODELING OF BEAM LOSS IN TEVATRON AND BACKGROUNDS INTHE BTEV DETECTOR ∗A.I. Drozhdin† , N.V. Mokhov, FNAL, Batavia, IL 60510, USAAbstractDetailed STRUCT simulations are performed on beamloss rates in the vicinity of the BTeV detector in the Teva-tron CØ interaction region due to beam-gas nuclear elas-tic interactions and out-scattering from the collimation sys-tem. Corresponding showers induced in the machine com-ponents and background rates in BTeV are modeled withthe MARS14 code. It is shown that the combination of asteel collimator and concrete shielding wall located in frontof the detector can reduce the accelerator-related back-ground rates in the detector by an order of magnitude.MODELING WITH STRUCT AND MARS14COYD49XE0(3) F17(2)YXD17(2) F48 F49FOA48 cellBO  IPAOAntiproton collimators cross-sectionProton collimators cross-sectionDO  IPPPX’,Y’E0(3)D49F17(2)X,YX’,Y’F48F49D17(2)X,YF49D17(2)F48F17(2)E0(3)D49EOFigure 1: Tevatron Run II beam collimation system.As a result of halo interactions with limiting apertures,hadronic and electromagnetic showers are induced in ac-celerator and detector components causing excessive back-grounds in the CDF and DØ collider detectors these daysand in the future BTeV detector. A two-stage collimationsystem has been developed for the Tevatron Run II [1] toreduce uncontrolled beam losses in the machine to an al-lowable level. About 0.1% of halo particles hitting the col-limators are scattered back into the beam pipe. These par-ticles are lost mostly in the high-β regions upstream of theexperimental halls producing the background rates in thedetector on the level of a few percent of those due to ppcollisions.To evaluate these rates for the BTeV detector, a multi-turn proton beam tracking through the Tevatron lattice with∗Work supported by the Universities Research Association, Inc., undercontract DE-AC02-76CH03000 with the U. S. Department of Energy.† drozhdin@fnal.gov 0 5e-10 1e-09 1.5e-09 2e-09 2.5e-09 3e-09 3.5e-09 4e-09 0  1000  2000  3000  4000  5000  6000Residual gas pressure, torPath length, mgas pressure 1 10 100 1000 10000 100000 1e+06 0  1000  2000  3000  4000  5000  6000Particle loss, part/secPath length, mloss distribution 0 200 400 600 800 1000 0  1000  2000  3000  4000  5000  6000Beam-gas hits, hits/m/secPath length, mF0 A0 B0 C0 D0 E0 F0hits produced loss at C0Figure 2: Residual gas pressure in the Tevatron Run-II(top), beam-gas induced loss distributions (middle) andbeam-gas hit distribution for protons lost at CØ (bottom).elastic beam scattering on the residual gas [2] and halointeractions with the collimators was conducted with theSTRUCT code [3]. All the accelerator components withtheir real strengths and aperture restrictions were taken intoaccount. Using the beam loss distributions calculated thisway in the vicinity of the CØ, detailed hadronic and elec-tromagnetic shower simulations with the MARS14 code [4]were performed in the machine, detector and tunnel com-ponents with a cutoff energy for hadrons, leptons and pho-tons of 0.1 MeV. Two protective measures – a short steelcollimator at the B48 location and a concrete shielding wallat the tunnel/hall interface on the proton side – were consid-ered as a way to reduce the machine-related backgrounds inthe BTeV detector.The Tevatron lattice, that corresponds to the BTeV op-eration, with β∗x,y=0.35 m at CØ was used without colli-sions at BØ and DØ (β∗x,y=1.7 m). The BTeV pixel de-tectors aperture radius is 2.75 mm (31σx,y), the CØ tripletquadrupoles aperture radius is 31.5 mm (14σx,y), and allother machine components with their strength and aper-tures were implemented in the model. The luminosity atCØ is assumed to be L = 2×1032cm−2s−1. The collima-tion system (Fig. 1) and residual gas pressure distribution(Fig. 2) of the Run-II [1, 2] were assumed in the model- 1 10 100 1000 10000 100000 3060  3080  3100  3120  3140  3160  3180  3200Particle loss, part/secPath length, mA11, A48 collim.                                                                3060  3080  3100  3120  3140  3160  3180  3200Path length, mcoll.B48CO 1 10 100 1000 10000 100000 3060  3080  3100  3120  3140  3160  3180  3200Particle loss, part/secPath length, mA11, A48, B48 collim. 1 10 100 1000 10000 100000 3060  3080  3100  3120  3140  3160  3180  3200Particle loss, part/secPath length, mA11, A48, B48 and additional coll.Figure 3: Beam-gas induced beam loss distributions in theCØ region: baseline (top), with B48 collimator (3-d line)and with additional collimator (bottom).ing. Detailed 3D geometry, magnetic field and materialsdescription in a 70-m region upstream of the CØ IP wereimplemented in the MARS14 model for lattice and tunnelcomponents along with a few meters of the dirt surround-ing the tunnel.RESULTSFor the current vacuum conditions, the nuclear elasticbeam-gas interactions is a dominant source of beam losson the electrostatic separators and low-β quadrupoles asshown in Table 1.Calculated beam loss distributions in the CØ region dueto elastic beam-gas interactions and collimation system in-efficiency are shown in Figs. 3 and 4 for the baseline layoutand the case with a 1.2-m long stainless steel collimator atthe B48 warm region upstream the last four SC dipoles pre-ceding the IP. The collimator jaws are at 12σx,y from thebeam axis, with their rectangular full aperture of 15.6 mm(hor.) and 4.6 mm (ver.). A further substantial reductionis possible with an additional short collimator located at12σx,y in ∼ 25 m upstream of the B48 one. Unfortunatelythis collimator should be placed in a short region betweensuperconducting magnets, that makes it difficult for real-ization.The calculations show that the B48 collimator in a com-bination with a recently installed A48 collimator protects 10 100 1000 10000 3060  3080  3100  3120  3140  3160  3180  3200Particle loss, part/secPath length, mA11, A48 coll.                                                                3060  3080  3100  3120  3140  3160  3180  3200Path length, mcoll.B48CO 10 100 1000 10000 3060  3080  3100  3120  3140  3160  3180  3200Particle loss, part/secPath length, mA11, A48, B48 coll. 10 100 1000 10000 3060  3080  3100  3120  3140  3160  3180  3200Particle loss, part/secPath length, mA11, A48, B48 and additional coll.Figure 4: Collimation system induced beam loss distribu-tions in the CØ region: baseline (top), with B48 collimator(3-d line) and with additional collimator (bottom).the BTeV pixel detectors and the low-β quads at an abortkicker prefire, reducing a number of particle lost by threeorders of magnitude.Particle flux isocontours (Eth=0.1 MeV) in the orbitplane in the 60-m long region preceding the BTeV exper-imental hall are presented in Fig. 5. Shown are neutronsin the baseline configuration and charged hadrons for thecase with the B48 collimator and a 2-m concrete wall at12.7 m upstream of the CØ IP. Fig. 6 shows hadron fluxXY-isocontours at the entrance to the hall (12.2 m from IP)for the case with the B48 collimator and shielding wall.Total background rates are summarized in Table 2. Thedominant component is photons: about 108 soft photonsper second (baseline) entering the hall around the beamline.There is no wall effect at R<0.25 m. The B48 collimatorTable 1: Beam loss rates (104 s−1) in the 70-m regionsupstream of DØ and BØ (now) and CØ (2009) with Run-IIvacuum parameters.Source DØ BØ CØNuclear elastic beam-gas 8.8 8.0 9.4Large angle Coulomb beam-gas 0.12 0.06 0.1Tails from collimators 2.4 3.5 0.99Elastic pp at two IPs 0.144 0.105 -C0 without B48 collimator and wall: Beam loss induced fluxes (MARS14)insideZY−300−1500150300cm−6.00e+03 −4.50e+03 −3.00e+03 −1.50e+03cm105 104 103 102 101 100 10−1 10−2 10−38.6e+03 0.0e+00Neutron fluence (cm^−2 s^−1) at V=+−20 cmZY−300−1500150300cm−6.00e+03 −4.50e+03 −3.00e+03 −1.50e+03cm105 104 103 102 101 100 10−1 10−2 10−38.2e+03 0.0e+00C0 with B48 collimator and wall: Beam loss induced fluxes (MARS14)insideCharged hadron fluence (cm^−2 s^−1) at V=+−20 cmFigure 5: Particle isofluxes in the CØ region: neutrons,baseline (top) and charged hadrons with B48 collimatorand 2-m concrete wall (bottom).alone reduces the backgrounds by a factor of two comparedto the baseline configuration. Installation of the shieldingwall results in a combined reduction effect of a factor often. The numbers in the table are to be increased by 10%to account for tails from the Tevatron main collimators.CONCLUSIONSA combined reduction of particle flow by a factor of 10is obtained from the B48 collimator and a 2-m concreteshielding wall at 12.7 m from the IP. Machine-related back-grounds at the last muon plane of the BTeV detector arequite low: 3.5 charged hadrons and 160 photons per cm2per second. With a 5-GeV cut this makes the machine-related backgrounds in the BTeV pixel detectors at a per-Table 2: Number of particles (105 s−1) above 0.1 MeVentering the BTeV hall at z=-12.2 m and R<3.5 m.Scenario n h± e± γ µ±No B48, no wall 24.2 14.5 58.9 1147 2.80B48, no wall 11.0 9.29 42.4 730 1.81B48, 2-m wall 6.29 2.48 7.55 132 1.00C0 with B48 collimator and wall: Beam loss induced fluxes (MARS14)insideV,YX−300−1500150300cm−300 −150 0 150 300cm103 102 101 100 10−1 10−2 10−3 10−4 10−51.6e+01 3.2e−02Neutron fluence (cm^−2 s^−1) at z=−12.2 mC0 with B48 collimator and wall: Beam loss induced fluxes (MARS14)insideYX−300−1500150300cm−300 −150 0 150 300cm103 102 101 100 10−1 10−2 10−3 10−4 10−51.2e+01 1.3e−04V,Charged hadron fluence (cm^−2 s^−1) at z=−12.2 mFigure 6: Neutron (top) and charged hadron (bottom)isofluxes at the entrance to the CØ hall, with B48 colli-mator and 2-m concrete wall.cent level of those from pp collisions. Calculations showthat a further substantial reduction is possible with an ad-ditional short collimator (unfortunately in the cold region)25 m upstream of the B48 one. Simulations show that B48collimator in a combination with a recently installed A48collimator protects the BTeV pixel detectors and the low-βquads at an abort kicker prefire.REFERENCES[1] M.Church, A.I.Drozhdin, A.Legan, N.V.Mokhov, R.Reilly,“Tevatron Run-II Beam Collimation System”, Proc. 1999PAC New York,p. 56, Fermilab-Conf-99/059 (1999).[2] A.I.Drozhdin, V.A.Lebedev, N.V.Mokhov, et al., “Beam Lossand Backgrounds in the CDF and DØ Detectors due to Nu-clear Elastic Beam-Gas Scattering”, Proc. 2003 PAC Port-land, OR, Fermilab-FN-734, Fermilab-Conf-03/088 (2003).[3] I.S.Baishev, A.I.Drozhdin, N.V.Mokhov, “STRUCT Pro-gram User’s Reference Manual”, SSCL–MAN–0034, 1994;http://www-ap.fnal.gov/∼drozhdin/[4] N.V.Mokhov, “The MARS Code System User’s Guide”,Fermilab-FN-628,1995; “Status of MARS Code”,Fermilab-Conf-03/053, 2003; http://www-ap.fnal.gov/MARS/.

Modeling of beam loss in Tevatron and backgrounds in the BTeV detector

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Modeling of beam loss in Tevatron and backgrounds in the BTeV detector

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