The High Energy LHC (HE-LHC) project is studying the feasibility of a new proton-proton collider with a beam energy of 13.5 TeV. The nominal optics features a β^{*} of 0.25 m and crab-cavities. Here we present a flat-beam optics that can be used with a non-zero crossing angle, in the absence of crab cavities. This is followed by energy deposition studies for the superconducting quadrupoles and dipole separators. The total dose in these magnets coming from the collision debris is evaluated

Abelleira, Jose Luis

Cruz Alaniz, Emilia

Seryi, Andrei

van Riesen-Haupt, Léon

The High Energy LHC (HE-LHC) project is studying the feasibility of a new proton-proton collider with a beam energy of 13.5 TeV. The nominal optics features a β^{*} of 0.25 m and crab-cavities. Here we present a flat-beam optics that can be used with a non-zero crossing angle, in the absence of crab cavities. This is followed by energy deposition studies for the superconducting quadrupoles and dipole separators. The total dose in these magnets coming from the collision debris is evaluate

Abelleira Fernandez, JL

Cruz-Alaniz, E

van Riesen-Haupt, L

Seryi, A

Oxford University Research Archive (ORA)

HE-LHC final focus: flat beam parameters and energy deposition studies

Abelleira Fernandez, Jose

Cruz-Alaniz, Emilia

van Riesen-Haupt, Leon

Oxford University Research Archive

HE-LHC FINAL FOCUS: FLAT BEAM PARAMETERS AND ENERGYDEPOSITION STUDIES ∗J. L. Abelleira, E. Cruz-Alaniz, L. van Riesen-Haupt, A. SeryiJohn Adams Institute, University of Oxford, UKAbstractThe High Energy LHC (HE-LHC) project is studying thefeasibility of a new proton-proton collider with a beam en-ergy of 13.5 TeV. The nominal optics features a β∗ of 0.25 mand crab-cavities. Here we present a flat-beam optics thatcan be used with a non-zero crossing angle, in the absence ofcrab cavities. This is followed by energy deposition studiesfor the superconducting quadrupoles and dipole separators.The total dose in these magnets coming from the collisiondebris is evaluated.THE HIGH ENERGY LHCThe High Energy LHC (HE-LHC) aims at providing ppcollisions at a center of mass energy of 27 TeV, making useof the existing LHC tunnel [1]. A large beam rigidity isimposed by the circulating 13.5-TeV beams in the 26.7-kmLHC tunnel, and requires the installation of 16-T bendingdipoles. To this purpose, the same magnet technology as forthe FCC-hh magnets can be applied [2].FINAL FOCUS DESIGNTwo high luminosity Interaction Regions (IR) are envis-aged at IR1 & IR5. An identical triplet at each side of bothIRs focalizes the beams at collision to maximize the luminos-ity. The design of this triplet is discussed in [3]. This finalfocus system is compatible with a round and a flat optics.The main parameters of the final focus quadrupoles, iden-tical for all of them, are shown in Table 1. The transversecross section of the FLUKA model for the magnets is shownin Fig. 1.Table 1: Quadrupole Parameters of the Final Focus TripletParameter ValueGradient 146 T/mInner radius 44.6 mmAbsorber thickness 20 mmInner coil radius 70.4 mmThe quadrupoles differ in length only, as seen in Fig. 2.Q2 consists of two units, and its gradient has opposite signto Q1 and Q3. The main parameters of the options discussedin this paper are shown in Table 2.∗ Work supported by EuroCircol, EU’s Horizon 2020 grant No 654305 &STFC grant to the John Adams Institute.Figure 1: Transverse cross section of the FLUKA model forthe triplet quadrupoles, including the tungsten shielding.Figure 2: Schematic of the final-focus triplet.FLAT BEAM OPTICSThe use of flat beams has been studied for the FCC-hhas an alternative to the use of crab cavities [4]. Flat beamsrestore some of the luminosity lost with the crossing angle inthe absence of crab cavities. This is achieved by reducing β∗ywhile the Piwinski angle (φ) is decreased through an enlargedβ∗x , as φ = θσs/2√ε β∗x , where θ is the full crossing angle,σs is the longitudinal beam size, and ε is the transverse beamemittance. If the beam separation (Δin) is kept, the crossingangle can be reduced too, as θ = Δin√ε/β∗x . However, thebeam separation must be enlarged as the flat beam ratio(β∗x/β∗y) increases [5]. This causes that part of the benefitof flattening the beam is diluted if the beam separation isincreased. Thus, the performance of the flat beam opticsdepends heavily on the beam separation.We have explored a range of parameters to define an opti-mum set of {β∗x , β∗y} for the flat option. We have looked atmaximizing the integrated luminosity without incurring ina large flat beam ratio, while keeping the total beam-beamparameter below 0.02 and the nominal luminosity below30·1034 cm−2s−1 [6]. With these constraints, an optimumworking point for the flat optics was found at β∗x=0.4 m,β∗y=0.1 m. In the worst case of having to increase the beamseparation by 50 %, the luminosity loss with respect to theround optics with crab cavities would be 16 %. On the otherhand, the luminosity loss of running the round optics withoutcrab cavities would be as large as 32 %.9th International Particle Accelerator Conference IPAC2018, Vancouver, BC, Canada JACoW PublishingISBN: 978-3-95450-184-7 doi:10.18429/JACoW-IPAC2018-MOPMK005MOPMK005356ContentfromthisworkmaybeusedunderthetermsoftheCCBY3.0licence(©2018).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOI.01 Circular and Linear CollidersA01 Hadron CollidersTable 2: HE-LHC parameter comparison of the different optics choices in this paper, round and flat. For the flat beamoption, two different beam separations are considerednominal flatBunch population, N [·1011] 2.2Normalized emittance, εN [μm] 2.5Number of bunches, nb 2808Bunch length, σs [cm] 7.55β∗x [m] 0.25 0.4β∗y [m] 0.25 0.1Beam separation, Δin[σ] 10 10/15Full crosing angle, θ[μrad] 260 208/312Crab cavities yes noPiwinski angle, φ 1.5 0.94/1.41Total tune shift ξt [ ·10−3] 20 16/11Nominal luminosity, L [·1034 cm−2s−1] 26 25/20Average luminosity, Lave [fb−1/day] 6.2 5.8/5.2Figure 3 shows the luminosity performance of the dif-ferent optics, until their respective optimum run time. Theoptimum run times are in the range from 3 to 4.1 h, assum-ing a preparation time between runs of 3 h. The luminositydecays due to the particle burn out, which is faster than theemittance damping time (3.6 h). For this reason, unlike theFCC-hh, there is no increase in luminosity. We can see thatthe performance of the flat optics with Δin = 10σ is almostidentical than that for round beams with crab cavities. ForΔin = 15σ, on the other hand, the luminosity is considerablylower, However, it is still better than for the case with roundbeams and no crab cavities. 0 5 10 15 20 25 30 0  1  2  3  4  5  6L [1034 cm-2s-1 ]t [h]round with crab cavitiesflat 10σflat 15σround without crab cavitiesFigure 3: Luminosity evolution for the round and flat optics.INTERACTION REGION OPTICSFigure 4 shows the betatron functions for the round op-tics, that present a maximum of 19 km. The correspondingbeam stay clear (BSC) is >12σ. The IR was designed withan optimization code [7] including several iterations withenergy deposition simulations. Other aspects of this triplet,including matching to the arc, dynamic aperture and injec-tion optics are also discussed in [3] .Figure 4: Interaction region for the round Optics (β∗ =0.25 m).ENERGY DEPOSITION SIMULATIONSThe debris from the pp collisions has been simulated withFLUKA [8,9] in order to guarantee the triplet survival duringthe entire lifetime, estimated in 10 ab−1. Energy depositionsimulations are shown in Fig. 5 for the round optics. Twocases are presented, with beam crossing in the horizontaland vertical plane, respectively. The radiation profile issymmetric on both sides of the interaction point. This isbecause the quadrupole is also symmetric from the referencesystem of the debris particles. The differences between thetwo crossing planes are caused by the quadrupolar fieldof the triplet magnets, which changes from focalizing todefocalizing for the horizontal and for the vertical plane.The vertical crossing presents higher peak doses, which canbe explained as Q1 and Q3 are defocalizing for this planewhile Q2 is focalizing.9th International Particle Accelerator Conference IPAC2018, Vancouver, BC, Canada JACoW PublishingISBN: 978-3-95450-184-7 doi:10.18429/JACoW-IPAC2018-MOPMK00501 Circular and Linear CollidersA01 Hadron CollidersMOPMK005357ContentfromthisworkmaybeusedunderthetermsoftheCCBY3.0licence(©2018).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOI.Figure 5: Peak dose profile for the round optics (θ =260 mrad).The maximum dose is found at Q1, and is lower than30 MGy, which is considered the present limit for the mag-net survival. In addition, the dose can be reduced if alternatecrossing is applied, as for each crossing plane, the peak isfound in a different location of the coil. This effect has beendiscussed for the FCC-hh final-focus [4, 10, 11]. The flatbeam scenario has also been simulated, without any signifi-cant difference in peak dose, in spite of the smaller crossingangle. Not only the quadrupoles are shielded, but the beampipe between magnets must be shielded too, otherwise alarge peak dose would appear at the begging of each magnet.However, for technical reasons, not all the space betweenmagnets can be shielded. Some space must be allocated forthe interconnects. In this study we have assumed intercon-nects of 50 cm. If we assume instead 100-cm interconnects,we observe peaks at the beginning of both Q2 units [12].Besides the peak dose, a very important aspect of to lookat is the peak power density absorbed on the magnet coils.An excessive power produces a temperature increase thatcan induce a magnet quench. This limit is considered to bewithin the range 3-5 mW/cm3 [13]. The peak power densityis shown in Fig. 6. The power density is below 3 mW/cm3,which indicates that the triplet is well quench protected.Figure 6: Peak power density for the round optics (θ =260 mrad).DOSE IN DIPOLE SEPARATION D1First studies have been carried out to estimate the dosein the first dipole separator, D1. This separation magnethas a length of 8 m and a magnetic field strength of 11.1 T.We have assumed coil aperture of 70 mm (radius), with ashielding of 5 mm, which gives a BSC > 30σ. Figure 7shows the radiation profile in D1 for the horizontal and ver-tical crossing. Peak dose is almost 100 MGy, considerablylarger than the limit. From these results we can concludenot only that D1 must be shielded, but that the thickness ofthe shielding must be more than 5 mm.Figure 7: Peak dose profile for D1.CONCLUSIONSWe have presented a final focus system which has beenoptimized to minimize the energy deposition in the coils.We have also shown the option of a flat-beam optics, whichis feasible with this triplet. We have found an optimum setof β∗x,y that can be used in case crab cavities technology isnot feasible for this machine. We have shown the strongdependence of the luminosity with the required beam sep-aration. First radiation studies for separation dipoles havebeen performed, showing the need for shielding in D1, atleast, in order to protect the superconducting coils. Morework will be carried out to minimize the dose in D1, andto extend this study to the other separation/recombinationdipole, D2.ACKNOWLEDGMENTSWe would like to acknowledge the collaboration withthe rest of the HE-LHC group and to the CERN FLUKAteam. In particular, we acknowledge Ilaria Besana for havingbuilt the FLUKA model of the FCC-hh quadrupole magnets,which was modified and re-scaled the HE-LHC magnets inthis study.9th International Particle Accelerator Conference IPAC2018, Vancouver, BC, Canada JACoW PublishingISBN: 978-3-95450-184-7 doi:10.18429/JACoW-IPAC2018-MOPMK005MOPMK005358ContentfromthisworkmaybeusedunderthetermsoftheCCBY3.0licence(©2018).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOI.01 Circular and Linear CollidersA01 Hadron CollidersREFERENCES[1] D. Amorim et al., “High-Energy LHC design”, presentedat IPAC’18, Vancouver, Canada, April-May 2018, paperMOPMF064.[2] D. Shulte et al., “ Future Circular Collider Study”, FCC week2018, Amsterdam, Netherlands, 2018.[3] L. van Riesen-Haupt et al., “Experimental Interaction RegionOptics for the High Energy LHC”, presented at IPAC’18,Vancouver, Canada, April-May 2018, paper MOPMK006.[4] J. L. Abelleira et al., “Energy Deposition Studies and Lumi-nosity Evolution for the Alternative FCC-hh Triplet”, pre-sented at IPAC’18, Vancouver, Canada, April-May 2018,paper MOPMK003.[5] T. Pieloni et al., “Beam Beam for the HE-LHC”, FCC Week2018, Amsterdam, Netherlands, 2018.[6] J. L. Abelleira et al., “HE-LHC with Flat beams”, FCC Week2018, Amsterdam, Netherlands, 2018.[7] L. van Riesen-Haupt et al., “A Code for Optimising TripletLayout”, in Proc. IPAC’17, Copenhagen, Denmark, May2017, paper TUPVA043, pp. 2163-2165.[8] A. Ferrari, P.R. Sala, A. Fassò, and J. Ranft, “FLUKA:a multiparticle transport code”, Rep. CERN-2005-10,INFN/TC05/11, SLAC-R-773, Oct. 2005.[9] G. Battistoni et al.,“Overview of the FLUKA code”, Annalsof Nuclear Energy, vol. 82, pp. 10-18, Aug. 2015.[10] Roman Martin et al., “Interaction region design driven byenergy deposition”, Physical Review Accelerators and Beams,Volume 20, 2017.[11] F. Cerutti et al., “Beam loss studies in IP”, FCC week 2018,Amsterdam, Netherlands, 2018.[12] J. L. Abelleira et al., “IR1 & IR5 Radiation Shielding”, FCCWeek 2018, Amsterdam, Netherlands, 2018.[13] Daniel Schoerling “Review of peak power limits for highluminosity IR triplet magnets”, FCC-hh other magnet designmeeting, 23 June 2018.9th International Particle Accelerator Conference IPAC2018, Vancouver, BC, Canada JACoW PublishingISBN: 978-3-95450-184-7 doi:10.18429/JACoW-IPAC2018-MOPMK00501 Circular and Linear CollidersA01 Hadron CollidersMOPMK005359ContentfromthisworkmaybeusedunderthetermsoftheCCBY3.0licence(©2018).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOI.

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HE-LHC Final Focus: Flat Beam Parameters and Energy Deposition Studies

HE-LHC Final Focus: Flat Beam Parameters and Energy Deposition Studies

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