CERN-ACC-2013-009 HiLumi LHC FP7 High Luminosity Large Hadron Collider Design Study Deliverable Report OPTICS AND LATTICE FILES Arduini, Gianluigi (CERN) et al 31 May 2013 The HiLumi LHC Design Study is included in the High Luminosity LHC project and is partly funded by the European Commission within the Framework Programme 7 Capacities Specific Programme, Grant Agreement 284404. This work is part of HiLumi LHC Work Package 2: Accelerator Physics & Performance. The electronic version of this HiLumi LHC Publication is available via the HiLumi LHC web site <http://hilumilhc.web.cern.ch> or on the CERN Document Server at the following URL: <http://cds.cern.ch/search?p=CERN-ACC-2013-009> CERN-ACC-2013-009
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CERN-ACC-2013-009
HiLumi LHCFP7 High Luminosity Large Hadron Collider Design Study
Deliverable Report
OPTICS AND LATTICE FILES
Arduini, Gianluigi (CERN) et al
31 May 2013
The HiLumi LHC Design Study is included in the High Luminosity LHC project and ispartly funded by the European Commission within the Framework Programme 7
Capacities Specific Programme, Grant Agreement 284404.
This work is part of HiLumi LHC Work Package 2: Accelerator Physics & Performance.
The electronic version of this HiLumi LHC Publication is available via the HiLumi LHC web site<http://hilumilhc.web.cern.ch> or on the CERN Document Server at the following URL:
HILUMI LHC FP7 High Luminosity Large Hadron Coll ider Design Study
Seventh Framework Programme, Capac i t ies Spec i f ic Programme, Research In f ras truc tures, Col laborat ive Pro ject , Design Study
DELIVERABLE REPORT
OPTICS AND LATTICE FILES DELIVERABLE: D2.1
Document identifier: HILUMILHC-Del-D2-1
Due date of deliverable: End of Month 18 (April 2013)
Report release date: 31/05/2013
Work package: WP2: Accelerator Physics and Performance
Lead beneficiary: CERN
Document status: Final
Abstract:
In order to achieve the HL-LHC goal in terms of integrated luminosity, a considerable reduction of the beam size at the high luminosity Interaction Points (IP) is needed. This is obtained by adapting the optics to achieve values of the so-called function as low as 15 cm at IP1 (ATLAS) and IP5 (CMS). The concept is based on the novel Achromatic Telescopic Squeezing (ATS) concept enabling both the matching of very low β* optics and the correction of the chromatic aberrations induced. New large aperture magnets will be needed in the inner triplet close to the interaction point, and its matching section, due to the strong beam divergence that is created by the extremely low β* values. A baseline layout including initial specifications for the new equipment has been delivered in close collaboration with WP3, resulting in a complete layout and optics for HL-LHC with 150 mm aperture in the inner triplet (IT) Nb3Sn quadrupoles operating at 140 T/m to replace the present low triplet. The layouts and magnet specifications have been defined and the main steps of the transition optics from injection to collision have been studied and are now available.
For more information on HiLumi LHC, its partners and contributors please see www.cern.ch/HiLumiLHC
The HiLumi LHC Design Study is included in the High Luminosity LHC project and is partly funded by the European Commission within the Framework Programme 7 Capacities Specific Programme, Grant Agreement 284404. HiLumi LHC began in November 2011 and will run for 4 years.
The information herein only reflects the views of its authors and not those of the European Commission and no warranty expressed or implied is made with regard to such information or its use.
Delivery Slip
Name Partner Date
Authored by G. Arduini, S. Fartoukh, B. Holzer, M. Giovannozzi, A. Wolski
CERN 13/05/2013
Edited by G. Arduini, S. Fartoukh, B. Holzer, M. Giovannozzi, A. Wolski
CERN 16/05/2013
Reviewed by L. Rossi (Project Coordinator) CERN 17/05/2013
1. EXECUTIVE SUMMARY In order to achieve the HL-LHC goal in terms of integrated luminosity, a considerable reduction of the beam size at the high luminosity Interaction Points (IP) is needed. This is obtained by adapting the optics to achieve values of the so-called function as low as 15 cm at IP1 (ATLAS) and IP5 (CMS). The concept is based on the novel Achromatic Telescopic Squeezing (ATS) concept enabling both the matching of very low β* optics and the correction of the chromatic aberrations induced. A key issue for the optics design and the lattice modifications is indeed to establish a smooth matching between the small Twiss parameters at the IP and the periodic arc. New large aperture magnets will be needed both in the new inner triplet close to the interaction point, and to equip the matching section of the new high luminosity insertions, due to the strong beam divergence that is created by the extremely low β* values. . A baseline layout including initial specifications for the new equipment has been delivered in close collaboration with WP3, resulting in a complete layout and optics for HL-LHC with 150 mm aperture in the inner triplet (IT) Nb3Sn quadrupoles operating at 140 T/m to replace the present low triplet. The layouts and magnet specifications have been defined and the main steps of the transition optics from injection to collision have been studied and are now available. A repository for optics and lattice files is available at /afs/cern.ch/eng/lhc/optics/HLLHCV1.0 and http://hllhcoptics.web.cern.ch/hllhcoptics/HLLHCV1.0/ .
2. INTRODUCTION In order to achieve the HL-LHC goal in terms of integrated luminosity, [1] a considerable reduction of the beam size at the high luminosity Interaction Points (IP) is needed. This is obtained by adapting the optics to achieve values of the so-called function as low as 15 cm at IP1 (ATLAS) and IP5 (CMS). The concept is based on the Achromatic Telescopic Squeezing (ATS) scheme [2] enabling both the matching of very low β* optics and the correction of the chromatic aberrations induced. This scheme was successfully tested in 2012 [3], but at low beam intensity and with zero crossing angle, because of the present aperture constraints. A key issue for the optics design and the lattice modifications is indeed to establish a smooth matching between the small Twiss parameters at the IP and the periodic arc. That is the first issue addressed and solved by the ATS scheme (which in some sense mismatch the -functions in the arcs in order to further squeeze *). New large aperture magnets will be needed in the inner triplet close to the interaction point due to the strong beam divergence that is created by the extremely low β* values. Depending on the magnet technology (Nb3Sn or Nb-Ti) that will be available, a number of beam optics has been developed to define the specifications for the new superconducting magnets. Quadrupole strength flexibility and chromatic corrections have been studied, the influence of the quadrupole fringe fields has been taken into account and the lattice in the matching section had been optimised including the needs of the crab cavities that will be installed. The transition between injection and low β optics has to guarantee smooth gradient changes over a wide range of β* values and the tolerances on misalignments and power converter ripple has been re-evaluated. Finally the successful combination of the quadrupole strengths in the high luminosity matching sections with those in the neighbouring IRs - a key concept of the ATS - plays an essential role to reach smallest β* values.
OPTICS AND LATTICE FILES
Doc. Identifier:
HILUMILHC-Del-D2-1
Date: 31/05/2013
Grant Agreement 284404 PUBLIC 5 / 14
A baseline layout including initial specifications for the new equipment has been specified in close collaboration with WP3, resulting in a complete layout and optics for HL-LHC with 140 mm aperture in the inner triplet (IT) quadrupoles [4, 5]. The decision was then taken to increase the aperture in the IT to 150 mm, to ensure full compatibility with the baseline * of 15 cm. At present the most promising solution is based on 150 mm aperture Nb3Sn quadrupoles operating at 140 T/m to replace the present low triplet. Aperture requirements for all other new magnets have been specified [6]. The layouts and magnet specifications are summarised in [7] and the main steps of the transition optics from injection to collision [8] have been studied and are now available, although the connection between the so-called pre-squeezed * of 44 cm and 15 cm is still missing for this layout. A repository for optics and lattice files is available at /afs/cern.ch/eng/lhc/optics/HLLHCV1.0 and http://hllhcoptics.web.cern.ch/hllhcoptics/HLLHCV1.0/ .
OPTICS AND LATTICE FILES
Doc. Identifier:
HILUMILHC-Del-D2-1
Date: 31/05/2013
Grant Agreement 284404 PUBLIC 6 / 14
3. THE HL-LHC V1.0 OPTICS
3.1. LAYOUT AND MAIN OPTICS CONSIDERATIONS
The HL-LHC lattice, established in tight collaboration with the other HiLumi-LHC work-packages and in particular with WP3, differs in a number of points from the existing LHC. The main differences are listed here:
A new triplet with orbit correctors and a corrector package (with orbit correctors and a series of multipole corrector coils including in particular skew decapole and dodecapole correctors and normal decapole correctors which are not available in the existing IT corrector package);
A superconducting 150 mm aperture separation dipole (D1) magnet;
Presently no qualitative layout change in the Matching Section, but new larger aperture magnets (D2/Q4/Q5), some magnet displacements (D2/Q5) and crab-cavities integrated between D2 and Q4/.
The main modifications as compared to the LHC standard lattice are listed in Table 1. Equipment to be changed
New (old) Aperture [mm] Separation [mm] (for 2-in-1)
Performance (T/m, T·m, MV,...)
TAS 60 (34) n/a n/a IT 150 (70) n/a 140 T/m D1 160 (80) n/a 35 40 T·m
Table 1: Main parameters of the new elements for HL-LHC [9].
One of the most crucial features of the HL-LHC upgrade project is the use of crab cavities to compensate for the geometric luminosity loss that is related to the crossing angle of the two beams. However a considerable crossing angle will be needed to avoid parasitic encounters of the 25 ns spaced bunches in the machine and to establish a 12.5 σ separation at each parasitic encounter. Accordingly, a crossing angle of 590 μrad has to be established at the high luminosity IPs. The new crossing scheme must be closed at D2 within the two crab-cavities per beam at each IP to avoid excessive requests on power on the cavities. This implies very strong orbit correctors (see Fig. 1). The requirements on the orbit correctors are listed in Table 2.
OPTICS AND LATTICE FILES
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Grant Agreement 284404 PUBLIC 7 / 14
Figure 1: Crossing scheme for the LHC (left) and for the HL-LHC (right). Courtesy of R. de Maria [9].
Magnets Location Aperture & Type Int. Strength [T·m] (rectangular spec for nested MCBX)
MCBX2a IP side of Q2a 150 mm – Nested HV 2.5 (×-plane) 2.5 (|| plane) MCBX2b nIP side of Q2b 150 mm – Nested HV 2.5 ((× -plane) 2.5 (|| plane) MCBX3 nIP side of Q3 150 mm – Nested HV 4.5 ((× -plane)2.5 (|| plane) MCBRD nIP side of D2 2-in-1 @ 105 mm,
not nested 7.0 ((× -plane) 2.0 (||-plane)
Table 2. Requirements on the orbit corrector of the triplet and D2 [9]. An example of a typical ATS optics is presented in Fig 2. It shows the beam optics in the complete LHC and the arc β‐beating waves that reflect the ATS scheme are nicely visible.
Figure 2: Horizontal and vertical Beam sizes in mm along the 27 km circumference of the LHC ring, assuming the nominal emittance of the LHC beam, for a typical ATS collision optics with IR1 and IR5 squeezed down to
*=10 cm (i.e. beyond the HL-LHC goal).
Following the beam optics calculations for the ATS scheme in IR1 and IR5, the flexibility of the optics in IR1 and IR5 has been investigated taking into account especially the β functions at Q4 where crab cavities will be installed. In addition optimal phase advances for IR2 and IR8, where the ALICE and LHCb detectors are located, had to be established that are
OPTICS AND LATTICE FILES
Doc. Identifier:
HILUMILHC-Del-D2-1
Date: 31/05/2013
Grant Agreement 284404 PUBLIC 8 / 14
compatible with ATS squeeze as well as low- optics for ion operations and injections. An example that illustrates the complexity is given for IR8 in Fig. 3. The optics has to be matched on the left side to the standard periodic FODO structure of the LHC arc, whereas, on the other side, the matching section and dispersion suppressor of this low-luminosity IR is used to create the β-beating wave which needed for the ATS scheme to squeeze down the beam sizes at the interaction point of the ATLAS experiment (IR1). Still at the same time the IR8 optics corresponds to a moderately low- insertion for the beam collisions in IP8.
Figure 3: IR8 optics: the IR quadrupole settings are defined to fulfil the optics matching conditions for standard FODO optics on the left, and the ATS scheme conditions on the right side, and at the same time the luminosity
requirements of the LHCb experiment. In red the vertical -function and in green the horizontal one.
In order to reach this goal in the large range of possible optics solutions, optimal phase advances have been identified for IR2 and IR8 that are compatible at the same time with the injection optics, and the various operation modes (proton and ion) and subsequent * requirements in the four LHC experimental experiments ATLAS, ALICE, CMS and LHCb.
The results achieved so far, the successful upgrade optics and layout, and the corresponding parameter space of the HL-LHC were published at the IPAC2012 conference [3,10].
3.2. OPTICS CORRECTION STRATEGIES AND TOLERANCES
Chromatic aberrations (Q’, but also Q”, Q’’’, and the off-momentum -beating) are under control thanks to the ATS principle. The spurious dispersion from the crossing-angle, otherwise fully mismatched and reaching up to 20-25 m in the IT at a *=10 cm can be controlled thanks to the ATS specific phase advance and orbit bumps in the arcs (see Fig. 4).
OPTICS AND LATTICE FILES
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Fig. 4. Spurious dispersion before (left) and after (right) correction [9]. Note the different scale.
The very small β* values achieved in the new optics design of the HL-LHC requires large apertures in the high gradient final focusing quadrupoles, which lead to considerably stronger fringe field effects compared to the LHC standard magnets. As a consequence a considerable influence is expected on the beam optics, and the magnet model used to describe the machine had to be improved to take these effects into account [11,12]. Taking into account the effect of the two high luminosity regions in HL-LHC, the re-calculated optics shows a difference in of up to 10%, which consumes about half of the allowed 20% tolerance in the LHC accelerator if left uncorrected. A rematch of the beam optics using the improved model can be used in all HL-LHC luminosity optics to overcome this problem. The small functions that are foreseen at the interaction points of the HL-LHC optics lead inevitably to large values of these parameters at the triplet quadrupole lenses. With a maximum of of about 22 km the resulting beam size as well as the sensitivity of the beam with respect to external tolerances is considerably increased compared to the LHC standard optics [13]. For each quadrupole magnet in the triplet and matching section the tolerances have been determined, keeping the overall budget of the resulting beat within the limit that has been defined for the LHC, ≤ 20%. The values obtained will act as input for the power converter and magnet design. In parallel the transition between the meanwhile well-established HL-LHC-injection optics and the collision optics were studied in particular for the transition between the injection optics and the so called pre-squeeze optics that results in a value at the IPs of β*=44 cm. A number of constraints concerning the phase advance, the tolerable beat and the boundary conditions from the magnet technology have to be met. At any moment a smooth transition is required for the quadrupole strengths. Step-like change in the normalized gradients, zero crossings of the gradients or situations that lead to intolerable hysteresis and saturation have to be avoided. A successful scenario for the ATS pre-squeeze has been developed fulfilling all these requirements (see Fig. 5) [8].
OPTICS AND LATTICE FILES
Doc. Identifier:
HILUMILHC-Del-D2-1
Date: 31/05/2013
Grant Agreement 284404 PUBLIC 10 / 14
Figure 5: Smooth gradient changes optimised for optics transition between injection and pre-squeeze optics.
3.3. OPTICS AND LATTICE FILES A full set of beam optics has been established and optimized for the different LHC operation modes. The following versions are available: ATS collision optics with β* =15 cm in both planes in the high luminosity IPs 1, 5 and
β*=10m and 3m in the low luminosity IPs 2 and 8, respectively (round beams). This is defined as the HL-LHC standard optics for luminosity operation in proton-proton mode;
ATS collision optics with round beams and β*=10cm (this represent an ultimate configuration allowing to push the * beyond the nominal one);
ATS flat beam collision optics with βx*=30 cm, βy
*=7.5 cm and going to the extreme flat beam optics with βx
*=5 cm, βy*=20 cm and βx
*=20 cm, βy*=5 cm;
injection optics in three different versions with β*=18 m, 11 m and 6 m in IP1, 5. The 6 m version is considered as the baseline scheme and it is used as the optics at the end of the acceleration;
pre-squeezed optics corresponding to an almost standard low- concept, but with additional matching constraint on the left and right phase advances, both needed for the chromatic correction and to enable the second (telescopic) part of the squeeze which will further decrease the β* to its final value of 15 cm by acting only on the matching quadrupoles of IR4,6,2,8.
heavy ion operation optics providing β*=44 cm in IP1, 5 and 50 cm in IP2, 8.
The collection of these beam optics is available in the LHC data base and can be used to re-calculate the optics or act as starting point for further studies. A repository for the optics and lattice files is available under /afs/cern.ch/eng/lhc/optics/HLLHCV1.0 and http://hllhcoptics.web.cern.ch/hllhcoptics/HLLHCV1.0/ . The scripts and subroutines were explained to the team members to get them familiar with the tools to be used and the special boundary conditions of the ATS scheme.
3.4. NEW MATCHING SECTION LAYOUT An optimization of the layout of the matching section (and the re-calculation of the corresponding optics) which might be needed in order to reduce the demand on the deflecting voltage of the crab-cavities is well advanced [14]. The possibility to increase the β-value close to Q4 where the new cavities will be installed has been studied, keeping the compatibility with the ATS, and showing as well a net improvement in terms optics flexibility (in particular a β* reach of 15 cm in non-ATS mode) but at a price to severely limit the injection β* to 3m (just compatible with aperture constraint at 450 GeV). The most promising modifications are based on a triplet like structure in Q4, Q5 and Q6 and especially on the option of adding a
OPTICS AND LATTICE FILES
Doc. Identifier:
HILUMILHC-Del-D2-1
Date: 31/05/2013
Grant Agreement 284404 PUBLIC 11 / 14
second Q7 to gain margin for the optics flexibility. Schematically the proposed modifications are shown in Fig. 6.
Figure 6: Proposed lattice changes (including additional hardware) to optimise for smaller crab cavity voltage.
If applied this additional lattice modifications and the installation of the new Q7 would allow to reduce the crab cavity voltage from 12.5 MV to 8.8 MV although the present crab cavity tests are very encouraging and seem to indicate that the required total voltage above mentioned is realistic [15]. Other alternative layouts have been studied in parallel to explore the parameter space of the LHC lattice. They include lattice modifications like a new layout of the matching section, replacing Q5 and Q6 by a doublet, reinforcing Q7 by a longer quadrupole and replacing Q4 by a quadrupole triplet. Lattice flexibility and low function at the IP [16] have been attained without the ATS concept but the solutions found show extreme chromatic effects.
4. FUTURE PLANS / CONCLUSION / RELATION TO HL-LHC WORK After re-optimization of the HL-LHC lattice, a full set of beam optics has been established and optimized for all relevant operation modes. The lattice and optics files are available in the HL-LHC data base for further use by the members of all the WP involved in the HL-LHC Project (e.g. for beam-dynamics considerations and simulations, collimation studies, energy deposition estimates, etc.) and define the baseline for the new 150mm triplet version, called HLLHCV1.0. Injection, flat top, pre-squeezed and ATS collision optics are available, including standard collision (β* =50 cm) optics for the low luminosity IPs 2, 8 (in non-ATS mode). Optics tolerances have been determined, the fringe field effects which are more prominent than in the LHC nominal case have been included and the transition between flat top and pre-squeezed optics has been demonstrated. Updates of the optics files will be made available whenever modification of the layout will be required and approved by the Parameter and Layout Committee taking into account of the progress in the design of the magnets and of the other components.
OPTICS AND LATTICE FILES
Doc. Identifier:
HILUMILHC-Del-D2-1
Date: 31/05/2013
Grant Agreement 284404 PUBLIC 12 / 14
5. REFERENCES [1] L. Rossi and O. Brüning, High Luminosity Large Hadron Collider A description for
the European Strategy Preparatory Group, CERN-ATS-2012-236: http://cdsweb.cern.ch/record/1471000/files/CERN-ATS-2012-236.pdf
[2] S. Fartoukh, An Achromatic Telescopic Squeezing (ATS) Scheme For The LHC Upgrade, CERN-ATS-2011-161, in Proceedings of the 2nd International Particle Accelerator Conference, S. Sebastian, Spain, 4 – 9 September 2011, C. Petit-Jean-Genaz, A. Blanco, I. Etxebarria, F. Perez, A. Wolski, V. Schaa, eds., p. 2088-2090, http://cdsweb.cern.ch/record/1382077/files/CERN-ATS-2011-161.pdf
[3] S. Fartoukh et al., CERN-ATS-Note-2013-004 MD.
[4] S. Fartoukh and R. De Maria, Optics and Layout Solutions for HL-LHC with Large Aperture NB3SN and NB-TI Inner Triplets, CERN-ATS-2012-136, in Proceedings of the 3rd International Particle Accelerator Conference, New Orleans, USA, 20-25 May 2012, C. Petit-Jean-Genaz, J. Corbett, eds., p. 145-147: http://cdsweb.cern.ch/record/1459916/files/CERN-ATS-2012-136.pdf
[5] A repository for the optics and layout of the HL-LHC with a 140 mm- 150 T/m inner triplet, available under /afs/cern.ch/eng/lhc/optics/SLHCV3.1b and http://hllhcoptics.web.cern.ch/hllhcoptics/SLHCV3.1b/ .
[6] S. Fartoukh, HiLumi-LHC Optics, Presentation given at the LARP CM18/HiLumi LHC Meeting, Fermilab, 7-9 May, 2012: https://indico.fnal.gov/conferenceOtherViews.py?view=standard&confId=5072
[7] R. De Maria, S. Fartoukh, A. Bogomyagkov, M. Korostelev (2013), HLLHCV1.0: HL-LHC layout and optics models for 150 mm Nb3Sn triplets and local crab-cavities, TUPF014 in IPAC13 Proceedings.
[8] M. Korostelev, A.Wolski, R. De Maria, S. Fartoukh, Optics Transition between Injection and Collision optics for the HL-LHC Upgrade Project, TUPFI051 in IPAC13 Proceedings.
[9] S. Fartoukh, HL-LHC overview from the AP point of view: baseline and latest emerging challenges, Joint LARP CM20/HiLumi Meeting, 8-10 April 2013, Napa Valley, California, https://indico.cern.ch/conferenceTimeTable.py?confId=183635#20121114
[10] B.Holzer, R. De Maria, A. Chance, B. Dalena, J. Payet, A. Bogomyagkov, R. Appleby, M. Korostelev, K. Hock, A. Wolski, C. Milardi, A. Faus-Golfe, J. Resta (2012), Optics and lattice optimizations for the LHC upgrade project, CERN-ATS-2012-231, in Proceedings of the 3rd International Particle Accelerator Conference, New Orleans, USA, 20-25 May 2012, C. Petit-Jean-Genaz, J. Corbett, eds., p. 151-153: http://cdsweb.cern.ch/record/1470609/files/CERN-ATS-2012-231.pdf
[11] B. J. Holzer, R. De Maria, S. Fartoukh CERN, A. Chancé, B. Dalena, J. Payet, CEA, A. Bogomyagkov, BINP SB RAS, R. B. Appleby, S. Kelly, M. B. Thomas, L. Thompson, M. Korostelev, K. M. Hock, A. Wolski, C. Milardi, A. Faus-Golfe, J. Resta Lopez, Optics Design and Lattice Optimisation for the HL-LHC, TUPFI023, in IPAC13 proceedings.
OPTICS AND LATTICE FILES
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[12] M. Thomas et al, Study of the Impact of Fringe Fields of the Large Aperture Triplets on the Linear Optics of the HL-LHC, WEPEA059, in IPAC13 proceedings.
[13] C. Milardi, HL-LHC Task 2.2 workshop, 19-20 September 2012: https://indico.cern.ch/conferenceDisplay.py?confId=208496
[14] B. Dalena et al., High Luminosity LHC Matching Section Layout vs. Crab Cavity Voltage, TUPFI001 in IPAC13 Proceedings.
[15] J. Delayen, Proof of Principle cavity preparation and testing: RFD Cavity, Joint LARP CM20/HiLumi Meeting, 8-10 April 2013, Napa Valley, California, https://indico.cern.ch/conferenceTimeTable.py?confId=183635#20121114
[16] R. Appleby et al, “LSS Layout Optimizations for Low-Beta Optics for the HL-LHC”, WEPEA058, in IPAC13 proceedings.
