Energy deposition in the superconducting magnets by particles from p-p collisions is a significant challenge for the design of the LHC high luminosity insertions. We have studied the dependence of the energy deposition on the apertures and strengths of insertion magnets and on the placement of absorbers in front of and within the quadrupoles. Monte Carlo simulations were made using the code DTUJET to generate 7 x 7 TeV p-p events and the code MARS to follow hadronic and electromagnetic cascades induced in the insertion components. The 3D geometry and magnetic field descriptions of the LHC-4.1 lattice were used. With a quadrupole coil aperture  70 mm, absorbers can be placed within the magnet bore which reduce the peak power density, at full luminosity, below 0.5 mW/g, a level that should allow the magnets to operate at their design field. The total heat load can be removed by a cooling system similar to that used in the main magnets

Mokhov, N V

Strait, J B

CERN Document Server

EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCHEuropean Laboratory for Particle PhysicsOPTIMIZATION OF THE LHC INTERACTION REGIONWITH RESPECT TO BEAM-INDUCED ENERGY DEPOSITIONJ. Strait*N. Mokhov**Energy deposition in the superconducting magnets by particles from p-p collisions is a significant challenge forthe design of the LHC high luminosity insertions.  We have studied the dependence of the energy deposition onthe apertures and strengths of insertion magnets and on the placement of absorbers in front of and within thequadrupoles.  Monte Carlo simulations were made using the code DTUJET to generate 7 x 7 TeV p-p events andthe code MARS to follow hadronic and electromagnetic cascades induced in the insertion components.  The 3Dgeometry and magnetic field descriptions of the LHC-4.1 lattice were used.  With a quadrupole coil aperture 70 mm, absorbers can be placed within the magnet bore which reduce the peak power density, at fullluminosity, below 0.5 mW/g, a level that should allow the magnets to operate at their design field.  The total heatload can be removed by a cooling system similar to that used in the main magnets.LHC Division*Detached from Fermilab, Batavia, Ill, USA**Fermilab, Batavia, Ill, USAEPAC 96, Sitges, Spain, June 1996Geneva, Large Hadron Collider ProjectCERNCH - 1211 Geneva 23SwitzerlandLHC Project Report 43Abstract26/07/96OPTIMIZATION OF THE LHC INTERACTION REGIONWITH RESPECT TO BEAM-INDUCED ENERGY DEPOSITIONN. Mokhov, Fermilab, Batavia, Illinois, USAJ. Strait, CERN, Geneva, SwitzerlandAbstractEnergy deposition in the superconducting magnets by parti-cles from p-p collisions is a significant challenge for the de-sign of the LHC high luminosity insertions. We have stud-ied the dependence of the energy deposition on the aper-tures and strengths of insertion magnets and on the place-ment of absorbers in front of and within the quadrupoles.Monte Carlo simulations were made using the code DTUJETto generate 7x7 TeV p-p events and the code MARS to fol-low hadronic and electromagnetic cascades induced in theinsertion components. The 3D geometry and magnetic fielddescriptions of the LHC–4.1 lattice were used. With aquadrupole coil aperture70 mm, absorbers can be placedwithin the magnet bore which reduce the peak power den-sity, at full luminosity, below 0.5 mW/g, a level that shouldallow the magnets to operate at their design field. The totalheat load can be removed by a cooling system similar to thatused in the main magnets.1 INTRODUCTIONThe Large Hadron Collider (LHC) [1] is designed to pro-duce p-p collisions atps=14 TeV and L = 1034cm 2s 1.The interaction rate of 8108s 1 represents a power of al-most 900 W per beam, the large majority of which is di-rected towards the low- insertions. Previous studies [2,3, 4] have identified this as a potentially serious problem.The quadrupole fields sweep the secondary particles into thecoils preferentially along the vertical and horizontal planes,giving rise to local peak power densityPmaxas much as anorder of magnitude larger than the average. Tests of porouscable insulation systems [5] cooled by a 1.9 K helium bathhave shown that for typical cable dimensions up to about1 mW/g of heat can be removed while keeping the helium in-side the cable below 2.2 K. This is the most important pointof this study, since too large Pmaxcould prevent the low-quadrupoles from reaching their required gradient.To minimize Pmax, we have studied its dependence onthe aperture of the front absorber and of absorbers placed in-side the magnets, the low- quadrupole coil diameters, andthe beam separation/recombinationdipole length. Solutionswhich satisfy the requirements with a reasonable safety mar-gin have been found.Permanent address: Fermilab, Batavia, Illinois, USAInternal  AbsorbersD1Q03Q3Q2bQ2aQ01Q1Front Absorber01 02 03 04 01 5 2 5 3 5 4 5 5 5 6 5z (m)r (mm)Figure 1: The LHC low- insertion including absorberswhich reach the 10 limit (injection/collision optics:solid/dashed line) for dcoil=70 mm quadrupoles.2 COMPUTER MODELLINGFig. 1 shows the LHC low- insertion [1, 6]. The innertriplet is made of four identical high-gradient quadrupoleswith coil inner diameter dcoil=70 mm [7] (Q1 and Q3 fo-cusing and Q2a and Q2b defocusing), which are poweredin series and operate at a maximum gradient of 227 T/mat the high luminosity IRs. Two independently powered“trim” quadrupoles of dcoil=85 mm and maximum operat-ing gradient of 120 T/m (Q01 and Q03) provide the addi-tional strength required by Q1 and Q3 and allow tuning ofthe triplet. Behind the triplet are the dipoles D1 (single aper-ture) and D2 (twin aperture). They havedcoil=85 mm and anoperating field of 4.3 T. Their length (11.5 m) is set by therequired strength at the combined experimental and injec-tion insertions (points 2 and 8), where space is more limitedthan at the high luminosity IRs (points 1 and 5).Alternate IR designs with quadrupoles of dcoil=60 mmand 80 mm have also been considered. The gradients werescaled with dcoil(a little more slowly than 1/r for thick shellquadrupoles) and corresponding length changes were made.Optics with minimal perturbations to the baseline were com-puted for injection (450 GeV, =6 m) and collision (7 TeV,=0.5 m) conditions and are summarized in Table 1. Rel-ative to the baseline 70 mm case maxfor 80 (60) mmquadrupoles changes by +6.6% (-5.1%) yielding changesin the maximum beam size of +3.3% (-2.6%), considerablyless than the change in dcoil. Thus increasing the apertureshould improve the field quality over the region occupied bythe beam and allow more shielding inside the magnet bore,Table 1: Characteristics of the IR optics.dcoil60 mm 70 mm 80 mmLmag5.1 m 5.5 m 6.0 mStage Coll. Inj. Coll. Inj. Coll. Inj.G (T/m)Q1-Q3 251 15.5 227 14.0 202 12.4Q01 70 4.7 80 5.3 92 6.1Q03 105 8.5 101 7.7 95 6.1max(m) 4204 358 4431 377 4724 402Table 2: Minimum inner radii of absorbers.dcoil60 mm 70 mm 80 mmClearance 10 10 8 10Collimator 14.0 14.0 12.0 14.0Q1 19.0 19.5 17.0 20.0Q01 21.5 21.5 18.5 22.0Q2-Q03 26.5 27.0 23.5 28.0D1 36.5 37.5 34.0 38.0while decreasing the aperture will have the opposite effect.A 1.8 m long copper absorber is placed in front of thetriplet and stainless steel absorbers are placed within themagnet bores to minimize the energy deposition in the coils.The LHC design requires [1] that the physical aperture, in-cluding effects of dispersion, closed orbit errors, construc-tion and alignment tolerances, and the crossing angle in theIRs, be everywhere at least 10 (except at the beam clean-ing collimators), where  is the rms beam size. Fig. 1 showsthe 10 limit for injection and collision conditions and ab-sorbers with inner radius rinat this limit. The cusp betweenQ2b and Q3 is where the maximum  changes from oneplane to the other. The outer radius of the internal absorbersis 2 mm less than rcoil. Table 2 gives rinof the absorbersfor the three quadrupole diameters. To allow the effective-ness of the absorber to be evaluated versus thickness for afixed insertion design, the rinfor 8 are given for the 70 mmquadrupoles. As the rcoilgrows from 30 to 40 mm the 10limits increase by only 0.5 mm (Q1-Q01) and 1.5 mm (Q2-Q03), allowing an increased absorber thickness. However,the D1 absorber decreases from 5.5 to 4 mm thick.The p-p collisions and showers in the IR components aresimulated with the DTUJET93 event generator [8] and theMARS code [9], version 13(96) respectively. Charged parti-cles are tracked through the lattice and the fields within eachmagnetic element. The cut-off energies are 1 MeV (chargedparticles), 0.2 MeV (photons) and 0.5 eV (neutrons). Mag-net coils are modeled with 4 radial bins of 8.5 mm depth, az-imuthal bins varying from 5 at the horizontal and verticalplanes to 15 between, and axial bins between 1.1 m (Q1)and 3.8 m (D1) long. The magnet coils, which are a mixtureof NbTi, copper, insulation and helium, are simulated as ahomogeneous material with A=50, Z=23 and =7 g/cm3.Details such as cooling channels in the yoke and coil endsare not included. Statistical errors on the Monte Carlo calcu-lation are estimated to be15% for Pmax,6% for the en-ergy deposited in each magnet, and1% for the total powerin the inner triplet, based on comparison of results from dif-ferent runs with independent random seeds.3 RESULTSFig. 2 shows Pmaxvs z for the IR with 70 mm quadrupolesand no internal absorbers, absorbers at 10 and 8, and allquadrupole absorbers of a uniform radius at the 10 limitin Q2-Q03. The front absorber aperture is set at 10 forthe case of no internal absorbers. With no internal absorberPmax= 1.20.2 mW/g, at or above the allowable limit.With individually sized 10 absorbers the peak is a factorof 3 smaller, giving a reasonable safety margin. Use of an8 absorber reduces Pmaxin Q1, but there is little over-all improvement. Increasing rinof the absorbers in Q1-Q01to match the other quadrupoles results in a 25% increase inPmax. However, this increase may not be statistically sig-nificant and further study will be required to determine if itis necessary to use different absorbers in Q1 and Q01 thanin the rest of the triplet.An unacceptably large Pmaxis observed at the back ofD1 even with a 10 absorber. However, at the high lumi-nosity IRs it is possible to move the outer dipole D2 up toan additional 90 m farther from D1. This would reduce thelength of D1 to one-third its present value, corresponding tothe first bin in Fig. 2, which has an acceptable power density.Alternatively the integrated strength would be low enoughto allow use of conventional magnets for D1 and D2, elim-inating the problem altogether.The cases of three quadrupole diameters with 10 ab-sorbers are compared in Fig. 3. Pmaxis 40% larger (30%smaller) with 60 mm (80 mm) quadrupoles than the baseline70 mm case. The reduced margin with dcoil=60 mm makesthis option unattractive. The 80 mm case has a significantlylarger margin, which could be used, if required, to provideadditional physical aperture. The larger maxis unlikely tobe a problem since the field quality in the region occupiedby the beam would be better with a larger aperture magnet.Shown also is the case in which all quadrupoles, includ-ing Q01 and Q03, have the same dcoil=70 mm and the ab-sorbers have a uniformrin. Pmaxis 80% larger than the casewith 85 mm trims and individually sized absorbers (Fig. 3)and 45% larger than with uniform absorbers (Fig. 2). Ap-parently it is unacceptable to have a continuous annular gapbetween the absorber outer and coil inner radii.Table 3 summarizes the total power deposited in the mag-nets and internal absorbers. The quadrupoles and the dipoleD1 are considered separately, since the actual dipole con-figuration will probably be different than that consideredhere. There is little difference among the cases with in-ternal absorbers. Up to half the power is deposited in theabsorbers, and it is tempting to consider cooling them at ahigher temperature. However, the insulating space betweenthe absorber and the vacuum pipe would reduce the absorbernone10 s8 suniform0.00.40.81.21.62 0 3 0 4 0 5 0 6 0z (m)Power Density (mW/g)Figure 2: Pmaxvs z for 70 mm quadrupoles with severalabsorber configurations.60 mm70 mm80 mm  70 mm Q01/Q030.00.20.40.60.82 0 3 0 4 0 5 0 6 0z (m)Power Density (mW/g)Figure 3: Pmaxvs z for main quadrupoles of threedcoilwith85 mm trim quadrupoles, and 70 mm main with 70 mm trimquadrupoles. The data are plotted at the z values for the70 mm quadrupoles to ease comparison.thickness, making this option impractical except possiblywith 80 mm magnets. The longitudinal power distributionis shown in Table 4 for 70 mm quadrupoles with 10 ab-sorbers. Averaged over each element, the power densityvaries from 3 W/m (Q2a) to 10 W/m (Q01). However, thevariation within one magnet can be as large as a factor of 8(Q1 with uniform diameter absorbers).4 CONCLUSIONSEnergy deposited in the superconducting magnets is an im-portant issue in the overall design of the LHC IRs. Re-ducing Pmaxto an acceptable level requires the use of in-ternal absorbers at least 5-6 mm thick. Quadrupoles withdcoil=70 mm, the current baseline design, are large enoughto accommodate such liners and leave a 10 physical aper-ture. A larger dcoilwould allow use of a thicker absorber,greater physical aperture for the same absorber thickness, orpossibly cooling the absorber at a higher temperature thanthe magnet. Pmaxin D1 at the high luminosity IRs is un-acceptably large if dipoles of the baseline length are used.However, here the dipoles can be moved farther apart reduc-ing their length by up to a factor of 3 or allowing the use ofconventional magnets.Table 3: Total deposited power (W).dcoil(mm) 70 70 70 70 60 80Absorber () none 10 10 8 10 10unifQuadrupoles 115 82 86 66 98 69Absorbers – 61 52 73 37 78Total 115 143 138 139 135 147D1 45 26 34 19 24 25Absorber – 10 16 15 12 9Total 45 36 50 34 36 34Table 4: Total power (W) deposited in each magnet for70 mm quadrupoles with 10 absorbers.Q1 Q01 Q2a Q2b Q3 Q03Magnet 15 6 13 17 26 4Absorber 18 10 5 9 13 7Total 33 16 18 26 39 115 ACKNOWLEDGEMENTSWe would like to thank P. Limon, R. Ostojic, K. Potter andT. Taylor for useful discussions. This work was supportedin part by the U.S. Department of Energy.6 REFERENCES[1] “The Large Hadron Collider Conceptual Design,”CERN/AC/95-05(LHC), 1995, P. Lefe`vre and T. Pet-tersson, editors.[2] K. Eggert and A. Morsch, “Particle Losses in the LHC In-teraction Regions,” CERN AT/93-17 (DI), 1993; A. Morsch,“Local Power Distribution from Particle Losses in the LHCInner Triplet Magnet Q1,” CERN AT/94-06 (DI), 1994.[3] A. Morsch, R. Ostojic, T.M. Taylor, “Progress in the SystemsDesign of the Inner Triplet of 70 mm Aperture Quadrupolesfor the LHC Low-beta Insertions,” Proc. 4th European Part.Accel. Conf., London, England, 1994.[4] N. V. Mokhov, “Accelerator/Experiment Interface at HadronColliders: Energy Deposition in the IR Components andMachine Related Background to Detectors”, Fermilab–Pub–94/085, 1994.[5] L. Burnod, et al., “Thermal Modelling of the LHC DipolesFuncitioning in Superfluid Helium,” Proc. 4th EuropeanPart. Accel. Conf., London, England, 1994.[6] R. Ostojic and T.M. Taylor, “Proposal for and ImprovedOptical and Systems Design of the LHC Low- Triplets,”CERN AT/94-38 (MA), 1994.[7] R. Ostojic, T.M. Taylor and G.A. Kirby, “Design and Con-struction of a One-Metre Model of the 70 mm ApertureQuadrupole for the LHC Low- Insertions,” Proc. 13th Int.Conf. on Mag. Tech. (MT13), Victoria, Canada, 1993.[8] P. Aurenche, et al., “DTUJET93”, Comput. Phys. Commun.,83, p. 107, 1994.[9] N. V. Mokhov, “The MARS Code System User’s Guide, Ver-sion 13(95)”, Fermilab–FN–628, 1995.

Optimization of the LHC Interaction Region With Respect to Beam-Induced Energy Deposition

Energy deposition in the superconducting magnets by particles from p- p collisions is a significant challenge for the design of the LHC high luminosity insertions. We have studies the dependence of the energy deposition on the apertures and strengths of insertion magnets and on the placement of absorbers in front of and within the quadrupoles. Monte Carlo simulations were made using the code DTUJET to generate 7{times}7 TeV p-p events and the code MARS to follow hadronic and electromagnetic cascades induced in the insertion components. The 3D geometry and magnetic field descriptions of the LHC-4.1 lattice were used. With a quadrupole coil aperture {ge}70 mm, absorbers can be placed within the magnet bore which reduce the peak power density, at full luminosity, below 0.5 mW/g, a level that should allow the magnets to operate at their design field. The total heat load can be removed by a cooling system similar to that used in the main magnets

Mokhov, N.V.

Strait, J.B.

UNT Digital Library

F Fermi National Accelerator LaboratoryFERMILAB-Conf-96/136Optimization of the LHC Interaction Region with Respect toBeam-Induced Energy DepositionN.V. Mokhov and J.B. StraitFermi National Accelerator LaboratoryP.O. Box 500, Batavia, Illinois 60510June 1996Presented at the European Particle Accelerator Conference,Barcelona, Spain, June 10-14, 1996Operated by Universities Research Association Inc. under Contract No. DE-AC02-76CHO3000 with the United States Department of EnergyDisclaimerThis report was prepared as an account of work sponsored by an agency of the United StatesGovernment. Neither the United States Government nor any agency thereof, nor any oftheir employees, makes any warranty, expressed or implied, or assumes any legal liability orresponsibility for the accuracy, completeness, or usefulness of any information, apparatus,product, or process disclosed, or represents that its use would not infringe privately ownedrights. Reference herein to any specic commercial product, process, or service by tradename, trademark, manufacturer, or otherwise, does not necessarily constitute or imply itsendorsement, recommendation, or favoring by the United States Government or any agencythereof. The views and opinions of authors expressed herein do not necessarily state or reectthose of the United States Government or any agency thereof.Optimization of the LHC Interaction Regionwith Respect to Beam-Induced EnergyDepositionN. V. Mokhov and J. B. StraityFermi National Accelerator LaboratoryP.O. Box 500, Batavia, Illinois 60510y On leave at CERN, CH-1211 Geneva, SwitzerlandJune 10, 1996AbstractEnergy deposition in the superconducting magnets by particles from p-p col-lisions is a significant challenge for the design of the LHC high luminosity inser-tions. We have studied the dependence of the energy deposition on the aperturesand strengths of insertion magnets and on the placement of absorbers in front of andwithin the quadrupoles. Monte Carlo simulations were made using the code DTUJETto generate 7x7 TeV p-p events and the code MARS to follow hadronic and elec-tromagnetic cascades induced in the insertion components. The 3D geometry andmagnetic field descriptions of the LHC–4.1 lattice were used. With a quadrupolecoil aperture 70 mm, absorbers can be placed within the magnet bore which re-duce the peak power density, at full luminosity, below 0.5 mW/g, a level that shouldallow the magnets to operate at their design field. The total heat load can be removedby a cooling system similar to that used in the main magnets.Presented at the European Particle Accelerator Conference, Barcelona, Spain, June 10-14, 19961Figure 1: The LHC low- insertions including absorbers which reach the 10 limit(injection/collision optics: solid/dashed line) for dcoil=70 mm quadrupoles.22 Computer ModellingFig. 1 shows the LHC low- insertion [1, 6]. The inner triplet is made of four iden-tical high-gradient quadrupoles with coil inner diameter dcoil=70 mm [7] (Q1 andQ3 focusing and Q2a and Q2b defocusing), which are powered in series and op-erate at a maximum gradient of 227 T/m at the high luminosity IRs. Two indepen-dently powered “trim” quadrupoles of dcoil=85 mm and maximum operating gradi-ent of 120 T/m (Q01 and Q03) provide the additional strength required by Q1 andQ3 and allow tuning of the triplet. Behind the triplet are the dipoles D1 (single aper-ture) and D2 (twin aperture). They have dcoil=85 mm and an operating field of 4.3 T.Their length (11.5 m) is set by the required strength at the combined experimentaland injection insertions (points 2 and 8), where space is more limited than at the highluminosity IRs (points 1 and 5).Alternate IR designs with quadrupoles of dcoil=60 mm and 80 mm have alsobeen considered. The gradients were scaled with dcoil (a little more slowly than 1/rfor thick shell quadrupoles) and corresponding length changes were made. Opticswith minimal perturbations to the baseline were computed for injection (450 GeV,=6 m) and collision (7 TeV, =0.5 m) conditions and are summarized in Table 1.Relative to the baseline 70 mm case max for 80 (60) mm quadrupoles changes by+6.6% (-5.1%) yielding changes in the maximum beam size of +3.3% (-2.6%), con-siderably less than the change in dcoil. Thus increasing the aperture should improvethe field quality over the region occupied by the beam and allow more shielding in-side the magnet bore, while decreasing the aperture will have the opposite effect.A 1.8 m long copper absorber is placed in front of the triplet and stainless steelabsorbers are placed within the magnet bores to minimize the energy deposition inthe coils. The LHC design requires [1] that the physical aperture, including effects ofdispersion, closed orbit errors, construction and alignment tolerances, and the cross-ing angle in the IRs be everywhere at least 10 (except at the beam cleaning colli-mators), where  is the rms beam size. Fig. 1 shows the 10 limit for injection andTable 1: Characteristics of the IR optics.dcoil 60 mm 70 mm 80 mmLmag 5.1 m 5.5 m 6.0 mStage Coll. Inj. Coll. Inj. Coll. Inj.G (T/m)Q1-Q3 251 15.5 227 14.0 202 12.4Q01 70 4.7 80 5.3 92 6.1Q03 105 8.5 101 7.7 95 6.1max (m) 4204 358 4431 377 4724 4023Table 2: Minimum inner radii of absorbers.dcoil 60 mm 70 mm 80 mmClearance 10 10 8 10Collimator 14.0 14.0 12.0 14.0Q1 19.0 19.5 17.0 20.0Q01 21.5 21.5 18.5 22.0Q2-Q03 26.5 27.0 23.5 28.0D1 36.5 37.5 34.0 38.0collision conditions and absorbers with inner radius rin at this limit. The cusp be-tween Q2b and Q3 is where the maximum  changes from one plane to the other.The outer radius of the internal absorbers is 2 mm less than rcoil. Table 2 gives rinof the absorbers for the three quadrupole diameters. To allow the effectiveness ofthe absorber to be evaluated versus thickness for a fixed insertion design, the rin for8 are given for the 70 mm quadrupoles. As the rcoil grows from 30 to 40 mm the10 limits increase by only 0.5 mm (Q1-Q01) and 1.5 mm (Q2-Q03), allowing an in-creased absorber thickness. However, the D1 absorber decreases from 5.5 to 4 mmthick.The p-p collisions and showers in the IR components are simulated with theDTUJET93 event generator [8] and the MARS code [9], version 13(96) respectively.Charged particles are tracked through the lattice and the fields within each magneticelement. The cut-off energies are 1 MeV (charged particles), 0.2 MeV (photons) and0.5 eV (neutrons). Magnet coils are modeled with 4 radial bins of 8.5 mm depth, az-imuthal bins varying from 5 at the horizontal and vertical planes to 15 between,and axial bins between 1.1 m (Q1) and 3.8 m (D1) long. The magnet coils, whichare a mixture of NbTi, copper, insulation and helium, are simulated as a homoge-neous material with A=50, Z=23 and =7 g/cm3. Details such as cooling channelsin the yoke and coil ends are not included. Statistical errors on the Monte Carlo cal-culation are estimated to be 15% for Pmax,6% for the energy deposited in eachmagnet, and 1% for the total power in the inner triplet, based on comparison ofresults from different runs with independent random seeds.3 ResultsFig. 2 shows Pmax vs z for the IR with 70 mm quadrupoles and no internal absorbers,absorbers at 10 and 8, and all quadrupole absorbers of a uniform radius at the10 limit in Q2-Q03. The front absorber aperture is set at 10 for the case of nointernal absorbers. With no internal absorber Pmax = 1.20.2 mW/g, at or abovethe allowable limit. With individually sized 10 absorbers the peak is a factor of 34none10σ8σuniform0.00.40.81.21.62 0 3 0 4 0 5 0 6 0z (m)Power Density (mW/g)Figure 2: Pmax vs z for 70 mm quadrupoles with several absorber configurations.smaller, giving a reasonable safety margin. Use of an 8 absorber reduces Pmax inQ1, but there is little overall improvement. Increasing rin of the absorbers in Q1-Q01 to match the other quadrupoles results in a 25% increase in Pmax. However,this increase may not be statistically significant and further study will be required todetermine if it is necessary to use different absorbers in Q1 and Q01 than in the restof the triplet.An unacceptably large Pmax is observed at the back of D1 even with a 10 ab-sorber. However, at the high luminosity IRs it is possible to move the outer dipoleD2 up to an additional 90 m farther from D1. This would reduce the length of D1 toone-third its present value, corresponding to the first bin in Fig. 2, which has an ac-ceptable power density. Alternatively the integrated strength would be low enoughto allow use of conventional magnets for D1 and D2, eliminating the problem alto-gether.The cases of three quadrupole diameters with 10 absorbers are compared inFig. 3. Pmaxis 40% larger (30% smaller) with 60 mm (80 mm) quadrupoles thanthe baseline 70 mm case. The reduced margin with dcoil=60 mm makes this optionunattractive. The 80 mm case has a significantly larger margin, which could be used,if required, to provide additional physical aperture. The larger max is unlikely to bea problem since the field quality in the region occupied by the beam would be betterwith a larger aperture magnet.Shown also is the case in which all quadrupoles, including Q01 and Q03, havethe same dcoil=70 mm and the absorbers have a uniform rin. Pmax is 80% larger than560 mm70 mm80 mm 70 mm Q01/Q030.00.20.40.60.82 0 3 0 4 0 5 0 6 0z (m)Power Density (mW/g)Figure 3: Pmax vs z for main quadrupoles of three dcoil with 85 mm trim quadrupoles,and 70 mm main with 70 mm trim quadrupoles. The data are plotted at the z valuesfor the 70 mm quadrupoles to ease comparison.the case with 85 mm trims and individually sized absorbers (Fig. 3) and 45% largerthan with uniform absorbers (Fig. 2). Apparently it is unacceptable to have a con-tinuous annular gap between the absorber outer and coil inner radii.Table 3 summarizes the total power deposited in the magnets and internal ab-sorbers. The quadrupoles and the dipole D1 are considered separately, since the ac-tual dipole configuration will probably be different than that considered here. ThereTable 3: Total deposited power (W).dcoil (mm) 70 70 70 70 60 80Absorber () none 10 10 8 10 10unifQuadrupoles 115 82 86 66 98 69Absorbers – 61 52 73 37 78Total 115 143 138 139 135 147D1 45 26 34 19 24 25Absorber – 10 16 15 12 9Total 45 36 50 34 36 346Table 4: Total power (W) deposited in each magnet for 70 mm quadrupoles with 10absorbers.Q1 Q01 Q2a Q2b Q3 Q03Magnet 15 6 13 17 26 4Absorber 18 10 5 9 13 7Total 33 16 18 26 39 11is little difference among the cases with internal absorbers. Up to half the power isdeposited in the absorbers, and it is tempting to consider cooling them at a highertemperature. However, the insulating space between the absorber and the vacuumpipe would reduce the absorber thickness, making this option impractical exceptpossibly with 80 mm magnets. The longitudinal power distribution is shown in Ta-ble 4 for 70 mm quadrupoles with 10 absorbers. Averaged over each element, thepower density varies from 3 W/m (Q2a) to 10 W/m (Q01). However, the variationwithin one magnet can be as large as a factor of 8 (Q1 with uniform diameter ab-sorbers).4 ConclusionsEnergy deposited in the superconducting magnets is an important issue in the over-all design of the LHC IRs. Reducing Pmaxto an acceptable level requires the useof internal absorbers at least 5-6 mm thick. Quadrupoles with dcoil=70 mm, the cur-rent baseline design, are large enough to accommodate such liners and leave a 10physical aperture. A larger dcoil would allow use of a thicker absorber, greater phys-ical aperture for the same absorber thickness, or possibly cooling the absorber at ahigher temperature than the magnet. Pmax in D1 at the high luminosity IRs is unac-ceptably large if dipoles of the baseline length are used. However, here the dipolescan be moved farther apart reducing their length by up to a factor of 3 or allowingthe use of conventional magnets.5 AcknowledgementsWe would like to thank P. Limon, R. Ostojic, K. Potter and T. Taylor for useful dis-cussions. This work was supported in part by the U.S. Department of Energy.7References[1] “The Large Hadron Collider Conceptual Design,” CERN/AC/95-05(LHC),1995, P. Lefèvre and T. Pettersson, editors.[2] K. Eggert and A. Morsch, “Particle Losses in the LHC Interaction Regions,”CERN AT/93-17 (DI), 1993; A. Morsch, “Local Power Distribution from Par-ticle Losses in the LHC Inner Triplet Magnet Q1,” CERN AT/94-06 (DI), 1994.[3] A. Morsch, R. Ostojic, T.M. Taylor, “Progress in the Systems Design of the In-ner Triplet of 70 mm Aperture Quadrupoles for the LHC Low-beta Insertions,”Proc. 4th European Part. Accel. Conf., London, England, 1994.[4] N. V. Mokhov, “Accelerator/Experiment Interface at Hadron Colliders: En-ergy Deposition in the IR Components and Machine Related Background toDetectors”, Fermilab–Pub–94/085, 1994.[5] L. Burnod, et al., “Thermal Modelling of the LHC Dipoles Funcitioning in Su-perfluid Helium,” Proc. 4th European Part. Accel. Conf., London, England,1994.[6] R. Ostojic and T.M. Taylor, “Proposal for and Improved Optical and SystemsDesign of the LHC Low- Triplets,” CERN AT/94-38 (MA), 1994.[7] R. Ostojic, T.M. Taylor and G.A. Kirby, “Design and Construction of a One-Metre Model of the 70 mm Aperture Quadrupole for the LHC Low- Inser-tions,” Proc. 13th Int. Conf. on Mag. Tech. (MT13), Victoria, Canada, 1993.[8] P. Aurenche, et al., “DTUJET93”, Comput. Phys. Commun., 83, p. 107, 1994.[9] N. V. Mokhov, “The MARS Code System User’s Guide, Version 13(95)”,Fermilab–FN–628, 1995.8

Optimization of the LHC interaction region with respect to beam-induced energy deposition

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Optimization of the LHC Interaction Region With Respect to Beam-Induced Energy Deposition

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