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Design of the Large Hadron Electron Collider Interaction Region

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Design of the Large Hadron Electron Collider Interaction Region PHYSICAL REVIEW SPECIAL TOPICS—ACCELERATORS AND BEAMS 18, 111001 (2015) Design of the large hadron electron collider interaction region E. Cruz-Alaniz* and D. Newton University of Liverpool, Liverpool L69 3BX, United Kingdom and Cockcroft Institute, Daresbury Laboratory, Warrington WA4 4AD, United Kingdom R. Tomás CERN, CH 1211 Geneva 23, Switzerland M. Korostelev Department of Physics, Lancaster University, Lancaster LA1 4YB, United Kingdom and Cockcroft Institute, Daresbury Laboratory, Warrington WA4 4AD, United Kingdom (Received 3 June 2015; published 5 November 2015) The large hadron electron collider (LHeC) is a proposed upgrade of the Large Hadron Collider (LHC) within the high luminosity LHC (HL-LHC) project, to provide electron-nucleon collisions and explore a new regime of energy and luminosity for deep inelastic scattering. The design of an interaction region for any collider is always a challenging task given that the beams are brought into crossing with the smallest beam sizes in a region where there are tight detector constraints. In this case integrating the LHeC into the existing HL-LHC lattice, to allow simultaneous proton-proton and electron-proton collisions, increases the difficulty of the task. A nominal design was presented in the the LHeC conceptual design report in 2012 featuring an optical configuration that focuses one of the proton beams of the LHC to βà ¼ 10 cm in the LHeC interaction point to reach the desired luminosity of L ¼ 1033 cm−2 s−1. This value is achieved with the aid of a new inner triplet of quadrupoles at a distance Là ¼ 10 m from the interaction point. However the chromatic beta beating was found intolerable regarding machine protection issues. An advanced chromatic correction scheme was required. This paper explores the feasibility of the extension of a novel optical technique called the achromatic telescopic squeezing scheme and the flexibility of the interaction region design, in order to find the optimal solution that would produce the highest luminosity while controlling the chromaticity, minimizing the synchrotron radiation power and maintaining the dynamic aperture required for stability. DOI: 10.1103/PhysRevSTAB.18.111001 PACS numbers: 41.85.-p I. INTRODUCTION AND MOTIVATION Particle physics has profited in the past from nucleon- The Large Hadron Collider (LHC) [1] at CERN with nucleon, lepton-nucleon and lepton-lepton interactions. The LHC has brought nucleon-nucleon collisions into circumference of 27p kmffiffiffi has been providing proton-proton collisions between s ¼ 7 TeV and 13 TeV, lead-lead the TeV era and the high luminosity Large Hadron pffiffiffi Collider (HL-LHC) [6] project aims to build on this success collisions at s ¼ 2.76 TeV=nucleon and proton-lead pffiffiffi by increasing the luminosity to 5 × 1034 cm−2 s−1 in IP1 collisions at s ¼ 5 TeV=nucleon in four different inter- and IP5. action points, ATLAS [2] in interaction point 1 (IP1), The large hadron electron collider (LHeC) aims to make ALICE [3] in interaction point 2 (IP2), CMS [4] in use of the LHC infrastructure and a new 60 GeV electron interaction point 5 (IP5) and LHCb [5] in interaction point accelerator to provide electron-proton (e-p) collisions, also, 8 (IP8). Each of these interaction points is located in its pffiffiffi in the TeV scale, aiming for an energy ( s ¼ 2 TeV) corresponding interaction region (IR). Other sections of the 4 times higher and a luminosity (1033 cm−2 s−1) 100 times ring, the interaction region 3 (IR3) and interaction region higher than the previous e-p collider, HERA [7]. The LHeC 7 (IR7) are reserved for collimation purposes. A layout of would work alongside the HL-LHC and provide a com- the LHC configuration is shown in Fig. 1. plementary set of measurements. This paper starts by describing the method to achieve high luminosity collisions in the HL-LHC experiments * e.cruz‑[email protected] using the achromatic telescopic squeezing (ATS) scheme in Sec. II. The nominal LHeC IR design status as it was Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distri- presented in the LHeC conceptual design report (CDR) bution of this work must maintain attribution to the author(s) and is described in Sec. III, at this point the integration into the published article’s title, journal citation, and DOI. the HL-LHC lattice was not yet successful. This paper 1098-4402=15=18(11)=111001(11) 111001-1 Published by the American Physical Society CRUZ-ALANIZ et al. Phys. Rev. ST Accel. Beams 18, 111001 (2015) in the IT generate huge chromatic aberrations that exceed the capabilities of the standard chromatic correction scheme performed by the sextupole families [9]. In order to further reduce the βà the achromatic tele- scopic squeezing (ATS) scheme [9] has been proposed to overcome the previous limitations as explained below. B. Basic principles of the ATS A standard matching procedure is done in the interaction regions to get a βà of 44 cm (named presqueezed βÃ) in the case of round beams optics. A further reduction of the presqueezed βà is followed by a telescopic squeeze, in which β-beating waves are gen- erated in the arcs adjacent to the high luminosity insertions, namely the arc sectors 45, 56, 81, and 12, by adjusting the quadrupole strengths in the neighboring straight sections, i.e. IR4, IR6, IR8 and IR2. A fundamental merit of this scheme is the locality of the chromaticity correction of the inner triplet by using one single arc of sextupoles on either side of IP1 and IP5. By adjusting the phase advance in the arc cell to π=2, the β FIG. 1. LHC schematic configuration showing clockwise beam waves generated in the arc reach their maximum at every 1 colliding with counterclockwise beam 2 in the four different other sextupole and the rate of increase of the β function is experiments [1]. proportional to the rate of decrease of the βà during the squeeze. This increase of the β function in the location of demonstrates the feasibility of the extension of the ATS these sextupoles enhances the efficiency of the chromaticity scheme into the LHeC IR, as described in Sec. IV. The correction to compensate the chromaticity produced by the flexibility of this design is also studied to explore the limits high β functions in the IT. on luminosity and the reduction of the synchrotron radi- This correction of the chromaticity also features the ation in the IR (Sec. V). Most importantly the chromatic control of the chromatic Twiss parameters. This is studied correction of the previous optical designs is addressed via the Montague functions which are given by and its limits explored (Sec. VI). The synchrotron radiation 1 pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi is studied to avoid too large background in the detector 2 2 W ¼ A þ B ; ð1Þ (Sec. VII). Lastly, particle tracking studies are done to 2 study the feasibility of such designs in terms of the stability of the beam (Secs. VIII and IX). where 1 ∂β II. HIGH LUMINOSITY COLLISIONS A ¼ ; ð2Þ β ∂δp The following sections introduce the HL-LHC current design, to later extend the study with the LHeC insertion ∂α in IR2. B ¼ − αA ð3Þ ∂δp βà A. Minimizing in HL-LHC and δp is the relative momentum deviation. The upgrade plans for the HL-LHC project include the Minimizing the Montague functions in the insertions implementation of a new inner triplet (IT) of high aperture IR3 and IR7 is required to not deteriorate the collimation quadrupoles. This inner triplet comprises three quadrupoles efficiencies. (Q1, Q2 and Q3) to the left and right of IP1 and IP5 [8]. The Montague functions have been studied previously Following the standard matching procedure [9] with for the LHC in [11] and the HL-LHC in [9], where further MADX [10], using as variables the strengths of the quadru- explanations about the overall ATS implementation can poles in IR1 and IR5, achieves a minimum value of βà in also be found. IP1 and IP5 respectively of about 30 cm. At this point The implementation of the ATS scheme provides a solid the mechanical acceptance of most of the magnets in the ground for the HL-LHC target of βà ¼ 15 cm in IP1 and matching section and the gradients of the matching quadru- IP5. Furthermore, the ATS scheme has also inspired a poles reach their limits. Furthermore, the high β functions telescopic squeeze implemented in the Relativistic Heavy 111001-2 DESIGN OF THE LARGE HADRON ELECTRON … Phys. Rev. ST Accel. Beams 18, 111001 (2015) TABLE I. L-R LHeC baseline and possible upgrade parameters. Baseline Upgrade Protons Electrons Protons Electrons Luminosity [1033 cm−2 s−1]111010 Beam energy (GeV) 7000 60 7000 60 Normalized emittance γϵx;y (μm) 3.75 50 2.5 20 βà (m) 0.1 0.12 0.05 0.10 rms beam size σx;y (μm) 7 7 4 4 rms beam divergence σx;y (μrad) 70 58 80 40 Beam current (mA) 430 (860) 6.4 1112 25 Bunch spacing (ns) 25 (50) 25 (50) 25 25 Bunch population [109] 1.7 × 102 1(2) 2.2 × 102 4 Bunch charge (nC) 27 0.16 (0.32) 35 0.64 Ion Collider (RHIC) to further reduce the βà [12]. The final IR design will need to incorporate an escape line for following sections explain the LHeC design to later on the neutral particles coming from the IP, probably requiring extend the ATS scheme to include the LHeC insertion. to split D1 into two parts separated by tens of meters. Bending dipoles around the IP are used to make the III.
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