A cascade calculation is done in the IR7 betatron cleaning insertion of LHC. It uses a detailed map of the primary losses and an accurate model of the straight section. One aim is to design a compact shielding which fits in the tight section of the tunnel. The same study allows to define radiation hardness properties of the equipment to be installed in the section and to locate areas of low activi ty for the installation of sensitive equipment

Azhgirey, L S

Baishev, I S

Catalan-Lasheras, N

Jeanneret, J B

CERN Document Server

EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCHEuropean Laboratory for Particle PhysicsLarge Hadron Collider Project LHC Project Report 184CASCADE SIMULATIONS FOR THE LHC BETATRON CLEANINGINSERTIONI. Azhgirey, I. Baishev, N. Catalan Lasheras and J.B. JeanneretAbstractA cascade calculation is done in the IR7 betatron cleaning insertion of LHC. It uses a detailedmap of the primary losses and an accurate model of the straight section. One aim is to design acompact shielding which ts in the tight section of the tunnel. The same study allows to deneradiation hardness properties of the equipment to be installed in the section and to locate areasof low activity for the installation of sensitive equipment.Paper submitted to the EPAC'98 Conference in Stockholm, 22 June 1998Member of the Russian collaboration to the LHC project,IHEP, Protvino, Russia.Administrative SecretariatLHC DivisionCERNCH-1211 Geneva 23SwitzerlandGeneva, May 1998CASCADE SIMULATIONS FOR THE LHC BETATRON CLEANINGINSERTIONI. Azhgirey, I. Baishev, IHEP, Protvino, RussiaN. Catalan Lasheras, J.B. Jeanneret, CERN, Geneva, SwitzerlandAbstractA cascade calculation is done in the IR7 betatron clean-ing insertion of LHC. It uses a detailed map of the primarylosses and an accurate model of the straight section. Oneaim is to design a compact shielding which fits in the tightsection of the tunnel. The same study allows to define ra-diation hardness properties of the equipment to be installedin the section and to locate areas of low activity for the in-stallation of sensitive equipment.1 INTRODUCTIONThe expected beam losses in collision at LHC might beas large as 8  1016 7 TeV protons per year in the beta-tron collimation insertion IR7 [1, 2, 3]. This implies theinstallation of a tight shielding in this area. The primarylosses before cascading will be distributed among 20 colli-mators. The small transverse size of the tunnel imposes tofit the shielding close to the equipments. Cascade calcula-tions must therefore be made with a detailed model of thestraight section.In this paper, we report on some preliminary calcula-tions. A first code is used to define a map of primary in-teractions. Then cascade simulations are made with twoversions of the geometry, one with a test version of shield-ing and one without it. Hadron fluences and absorbed dosesare computed at the surface of a cylinder surrounding thebeam lines.2 THE CLEANING INSERTION IN IR7The collimation system of LHC requires a section of ringwhich offers a betatronic phase advance of x= y2. This section must not be superconducting to sustain ahigh level of power deposition [1]. It will be made of sixquadrupoles each made of several modules. Two bendingmagnets will be installed at each end of the section to keepthe beam line free of the high flux of neutral particles emit-ted at the primary collimators.The principles of optics used for a collimation insertionand a discussion of the specific case of the version 5.0 ofIR7 in LHC can be found in [3]. The description in [1]was related to the older version 4.2 of the insertion, but thebasics of the geometry has not changed.In this calculation, the primary collimators are made of200 mm long aluminium jaws and the secondary ones of500 mm long copper jaws. These numbers are still openparameters, but are very unlikely to change drastically.A map of primary inelastic collisions is prepared withthe K2 code [3, 4] for further cascade calculations. To getan approximately realistic map of impact on primary col-limators, a proton is circulated inside the primary apertureusing one turn linear motion superimposed with a variabletransverse drift speed until it touches a collimator. Then, atracking with smaller steps is made, with linear betatronicmotion between collimators .In the collimator a Monte-Carlo method is used to sim-ulate coherent and incoherent nuclear elastic and Ruther-ford scattering. Multiple Coulomb scattering is treated as acontinuous diffusion process, iterating the motion near theedge of the collimator with high care. When an inelastic in-teraction occurs, the tracking is stopped and the coordinatesof the proton at the interaction point are stored. The map ofinelastic interactions is obtained by tracking ten thousandprotons.3 3D MODEL OF IR7The model of the cleaning section is based on the lat-tice version 5.0. It is described as a sequence of ele-ments aligned in accordance with the optical layout. Theelements are primary and secondary collimators, warmdipoles, warm quadrupoles and dipole correctors. Beampipes in the drift spaces between magnets and collimatorsare also treated as separate elements.In the right Cartesian coordinate system (x, y, z) the lon-gitudinal axes of symmetry of dipoles and quadrupoles be-long to the axis z. Beam axes of Ring 1 and Ring 2 liein parallel to the axis z in the horizontal plane (x, z). Theentire chain of elements is fully symmetric with respect tothe horizontal plane i.e. has vertical symmetry and is hor-izontally asymmetric because of the location of the orbitcorrectors and collimators.Every collimator tank is presented as a pair of jaws ina vacuum box. The longitudinal axis of a collimator coin-cides with the beam axis of Ring 1 or Ring 2. There arefour primary collimators in the system : horizontal, ver-tical, and at normalised X   Y azimuths 45 and 135.Every secondary collimators has an individual position andan individual X   Y azimuth [5].The warm dipole and quadrupole modules MBW andMQW are described in [6]. The two-dimensional mapsof the magnetic field [7] are used to simulate the cor-rect transport of charged particles in the dipoles and thequadrupoles. The warm dipole correctors are placed nearevery quadrupole in pairs so that the vertical corrector ofRing 1 is accompanied by the horizontal corrector of Ring 2and vice versa. Every corrector consists of one moduleMCBW [8].The beam pipes of both rings are copper tubes. The beampipe inside magnets and in the short drift spaces betweenmagnets has 44 mm inner diameter and 48 mm outer di-ameter and the inner diameter of the regular beam pipe inthe long drift spaces is 100 mm and the outer diameter is105 mm [9].Reasonable maximum of material around the beam linesis the first approach to the shielding design of the cleaningsystem. Iron shielding covers all the long drifts betweenmagnets. The typical transverse cross-section of the shield-ing is shown in Figure 1. Its outer dimensions are limitedmainly by the free space for the passage-way in the tun-nel. The inner dimensions are determined by the minimumspace required for the beam pipes or collimators.-75-50-250255075-75 -50 -25 0 25 50 75IronConcreteY, cmX, cmFigure 1: The shielding cross-section. The small centralcircles are the beam pipes in drift sections. The upper rightcircle is a survey device. The large circle is a scoring sur-face.4 RESULTSHadronic and electromagnetic cascades simulations wereperformed with the last version of the MARS code [10].Energy cut-off for hadron transport was 10 MeV. A thin(1 cm) cylindrical vacuum layer surrounding the whole as-sembly of elements was used for scoring the rate of outgo-ing particles (see Figure 1). The scoring shell was subdi-vided longitudinally in one metre long steps. To computedoses, the same cylinder layer was filled with polystyrenein a separate calculation.The results for hadron flux density presented in Figure 2were obtained assuming 109 primary interactions per sec-ond at 7 TeV in the collimators of one ring [2]. The struc-ture of the single-beam distributions 2a) and 2b) reflectsboth the map of primary interactions and the spread of highenergy secondaries along the beamline. The superposition2c) of the single-beam distributions is practically symmet-ric with respect to the crossing point IP7 at z = 251 m.Fluence attenuation by the shielding is the better thelonger is the distance from the closest source of radiation.The attenuation factor is equal to approximately 4 near thecollimators and grows up to 20 a few metres downstreamof them.Hadron fluence is a good indicator with respect to theradioactivation of the machine components, cooling water,air in the tunnel and rock outside. Absorbed dose is the bet-ter indicator with respect to the radiation damage of cableinsulation and other organic parts of equipment. The an-nual doses in Figure 3 were obtained for average expectedlosses of 1:6 1016 primary interactions in the collimatorsof one ring per year [2].Shielding effect in the case of absorbed dose is muchbetter than in the case of hadron fluence as can be seenin Fig.3. The dose attenuation factor is equal to 20 nearthe collimators and above a hundred at a distance fromthem. Absorbed dose in the case without shielding exceeds104 Gy/year almost everywhere. This level is dangerousfor the generic organic insulations. With shielding only afew hot spots with the annual dose above 103 Gy can befound. More detailed maps of doses and fluences may befound in [11].5 FURTHER WORKUnder the present assumptions, the calculated fluences atthe coils of the magnets are low enough to allow for us-ing organic insulation. But, to avoid peaks of irradiation atsome locations additional internal shielding will be mod-elled with further simulations. Calculation of activation ofthe air and of the rock outside the tunnel are under workusing the present map of fluences.6 ACKNOWLEDGMENTSThe authors would like to thank K. Potter, G.R. Stevensonand T. Taylor for their help and support along this study.7 REFERENCES[1] ”The Large Hadron Collider - Conceptual Design”,CERN/AC/95-05 (LHC), 1995.[2] M.Hofert et al., CERN/TIS-RP/IR/95-19.1, 1995.[3] N.Catalan Lasheras et al., CERN LHC Report 156, 1997.[4] T.Trenkler, J.B.Jeanneret, CERN SL/Note 94-105(AP),1994.[5] D.I.Kaltchev et al., CERN LHC Project Report 134, 1997.[6] M.Giesch, CERN AT/95-04; CERN LHC Note 323, 1995.[7] G.DeRijk, CERN LHC Project Note 100, 1997.[8] G.DeRijk, Proceedings of this Conference.[9] A.G.Mathewson, S.Zhang, CERN AT-VA 95-23, 1995.[10] I.L.Azhgirey et al., in: Ann. of XV Workshop on Charg.Part. Acc., p.74, Protvino, 1996.[11] I.L.Azhgirey et al., CERN LHC Project note 121, 1997.10 410 510 610 7F, cm-2   s-1Beam 110 410 510 610 7 Beam 210 410 510 610 70 25 50 75 100 125 150 175 200 225 250z, mBeams 1+2500-50Y, cmRing 2Ring 1Figure 2: Hadron flux density around the beam lines. Clear histograms - the case without shielding, grey histograms -the case with shielding. The z-range covers a half of the staight section. Beam enters at z=0, where the primary collimatorsare located. F(z) in z=[250,500] for beam 2 is similar to F(z) for beam 1 left-right reflected.10 210 310 410 50 25 50 75 100 125 150 175 200 225 250z, mD a, Gy  yr-1Figure 3: Above, a schematic layout of the cleaning insertion. Dark hatched surfaces stand for magnets and light hatchedones for shielding. Collimators appear as thin vertical lines in the shielding elements. Below, annual absorbed dose inorganic material around the beam lines.

Cascade Simulations for the LHC Betatron Cleaning Insertion

Abstract

Similar works

Full text

Available Versions

CERN Document Server