Technological Challenges for the LHC Upgrade Ingrid-Maria Gregor, - - PowerPoint PPT Presentation
Technological Challenges for the LHC Upgrade Ingrid-Maria Gregor, DESY a detector physicists view . LISHEP2011 Interna0onalSchoolofHEP RiodeJaneiro,Brazil July9,2011 100 Outline The LHC (current status)
Ingrid-Maria Gregor, DESY
Interna0onal School of HEP
Ingrid-Maria Gregor, DESY - Challenges at High Lumi LHC
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Apologies for the many interesting topics I didn’t cover!
The LHC (current status) Future Plans Overview Beam parameters and what they mean Beam Intensity Higher Field Magnets Luminosity Leveling Crab Cavities Conclusions
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LEP e+e- (1989-2000) 104 GeV/c per beam LHC pp and ions 7 TeV/c per beam 26.8 km length 8.3 Tesla superconducting magnets
(100m below surface) SPS accelerator
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Last magnet: April 26th 2007
Ingrid-Maria Gregor, DESY - Challenges at High Lumi LHC
The LHC surpasses existing accelerators/colliders in many aspects : The energy of the beam of 7 TeV that is achieved within the size constraints of the existing 26.7 km LEP tunnel. LHC dipole field 8.3 T HERA/Tevatron ~ 4 T The luminosity of the collider that will reach unprecedented values for a hadron machine:
Very high field magnets and very high beam intensities: Operating the LHC is a great challenge. There is a significant risk to the equipment and experiments. A factor 2 in field A factor 4 in size A factor 30 in luminosity
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Ingrid-Maria Gregor, DESY - Challenges at High Lumi LHC
7 based on graph from R.Assmann
Livingston type plot: Energy stored magnets and beam Potential equipment damage in case of failures during operation.
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Year Top energy [GeV] Length [m] Linac PSB PS SPS LHC 1979 0.05 30 1972 1.4 157 1959 26.0 628 1976 450.0 6911 2008 7000.0 26657
Ingrid-Maria Gregor, DESY - Challenges at High Lumi LHC
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Accelerator complete Ring cold and under vacuum 10.09: First beams around 19.09: Accident
2008 –2009
14 months of major repairs and consolidation NewQuench Protection System for online monitoring and protection of all inter-magnet joints But: uncertainties about the splice quality (copper stabilizer) Risk of thermal runaway scenarios => decision to limit beam energy to 3.5 TeV for first operation 20.11. Restart LHC at 1.18TeV 29.11: Both beams accelerated to 1.18 TeV simultaneously -> LHC Highest Energy Accelerator
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2010
19.03 Ramp to 3.5 TeV Collisions at 3.5+3.5 TeV LHC Reaches target energy for 2010/2011
2011
22.04: LHC sets world record beam intensity record broken almost on daily basis more Tops recorded than Tevatron …..
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https://twiki.cern.ch/twiki/bin/view/AtlasPublic/ LuminosityPublicResults#2011_pp_Collisions LHC Design July 2011
Momentum at collision [TeV/c] 7 3.5 Luminosity [cm-2s-1] 1.00E+34 1.26E+33 Number of bunches per beam 2808 1380 Bunch intensity 1.15E+11 1.25E+11
The performance of LHC is excellent Within a few months the goal for the year 2011 was reached: 1fb-1 ! Hopes are up to reach 5 fb-1 in 2011...
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Operation at even higher luminosity has three main purposes:
Perform more accurate measurement on the new particles discovered in the LHC Observe rare processes (predicted or newly discovered) with rates below the current sensitivity Extend the exploration of the energy frontier, extending the discovery reach by probing rare events. Besides the with to increase the luminosity there are some more technical reason: Radiation damage limit of IR quadrupoles ~400/fb ->~2020 this limit will be reached Hardware and shielding has not really been optimized for very high radiation Necessity to increase the heat removal capacity Restoring cooling capacity in IR5 left and decouple RF from magnets
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Error halving time (years)
Ingrid-Maria Gregor, DESY - Challenges at High Lumi LHC
Run until end of 2012 constantly improvements of the beam parameters (i.e. bunch spacing) Shut down for ~15 month to fully repair all ~10000 joints (non superconducting between SC magnets)
Resolder, install clamps …. Tie in LINAC4 (high intensity)
Shut down in 2018
collimation upgrade (dispersion suppressors) preparation for crab cavities & RF cryosystem detector upgrades
Shut down in ~2021
Full luminosity: 5x1034 leveled New inner triplets based on Nb3Sn Crab cavities
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“So to achieve high luminosity, all one has to do is make high population bunches of low emittance to collide at high frequency at locations where the beam optics provides as low values of the amplitude functions as possible.” PDG 2010, chapter 25
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Parameter Unit nominal upgrade Energy [TeV] 7 Protons/Bunch [1011] 1.15 1.7 Bunch Spacing [ns] 50…25 50…25 εn (x, y) [μm] 3.75 3.75 σz (rms) [cm] 7.55 7.55 Bunch Length (4 σ) [ns] 1.0 1.0 Longitudinal Emittance [eVs] 2.5 2.5 β* at IP1, IP5 [m] 0.55 0.25…0.14 Betatron Tunes {64.31, 59.32} {64.31, 59.32} Piwinski parameter: 0.65 1.4…2.5 BB Parameter, ξ , per IP 0.003 0.005…0.008 Crossing‐angle: θc [μrad] 285 315…509 Main RF [MHz] 400 400 Crab RF [MHz] 400 Peak luminosity w/o crab cavity 1034 cm‐2s‐1 1 3.3…3.8 Peak luminosity with crab cavity 1034 cm‐2s‐1 1.2 5.8…10.3 Pile up events per crossing 19 44…280
2 100
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n1 n2 Interaction Region area A with is the beam envelope at the IP; determined by the magnet arrangement and powering beam emittance (the extent occupied by the
particles of the beam in space and momentum phase space as it travels)
area A for a bunched beam luminosity “head on collision”
Beta function
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Angle at IP to avoid that the bunches collide in other places that the IP Crossing angle reduces luminosity “Piwinski parameter” effective cross section Piwinski parameter describes the effect that the crossing angle is affecting the beam dynamics The shorter the bunches ( ) the smaller is the effect
Geometry factor 2 2
effective cross section
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β* Brightness Geometry Factor Number of bunches Energy
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Ingrid-Maria Gregor, DESY - Challenges at High Lumi LHC
Provide passive protection against irregular fast losses and failures. Provide cleaning for slow losses in the super-conducting environment. Manage radiation impact of beam loss. Minimize background in the experiments.
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LHC has almost 100 collimators and absorbers. Alignment tolerances < 0.1 mm to ensure that over 99.99% of the protons are intercepted. The presently installed LHC collimation system provides
beam intensity of 40% with respect to nominal. beam 1.2
http://indico.cern.ch/conferenceDisplay.py?confId=139719
Ingrid-Maria Gregor, DESY - Challenges at High Lumi LHC
Primary 6 σ Secondary 8.8 σ Dump Protection 10.5 σ Tertiary 15 σ Triplet 18 σ
With collisions the aperture limit of the LHC is in the strong focusing quadrupoles (triplets) that are installed just next to the experiments.
Hierarchy of collimators must be preserved in all phases to avoid quenching super- conducting magnets and for damage protection. β* is presently limited to 3.5 m by aperture and tolerances.
Collimation hierarchy Exp.
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Ingrid-Maria Gregor, DESY - Challenges at High Lumi LHC
Limited in LHC by collimation system to ~ 20% at 3.5TeV Under certain assumptions on loss rates, imperfections Injectors can deliver nominal beams With experience assume that LHC can Move to tight collimator settings Improve loss rates Get the imperfection factor down
✦ Should allow to push to higher intensities (to ~40% nominal)
Then need to install something more Collimators in the cold regions of the machine in 2012 Using “missing magnet” space in the dispersion suppressors Requires moving magnets in LSS3 and LSS7 (24 magnets each) Should allow us to get to nominal intensity at 7TeV Phase II collimators installed in 2018
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Dispersion suppressor Matching section Separation dipoles Final focus
Today: 6x3 m x1.5 T; h=80 mm HL-LHC: 1x4 m x 7 T; Ø=150 mm Today: Two-in-One Ø =56 mm; 4.2K HL-LHC: Two-in-One Ø70 mm; 1.9 K Today: Q4 Two-inOne Ø=70 mm, 4.2 K; D2 ↑↑ 9 m x 3.5 T, 4.2 K HL-LHC: Q4 Two-in-One Ø=90 mm, 1.9 K; CRAB CAVITY; D2 ↑↑ 9 m x 5 T; 1.9 K Today MQX: 4 x 6 m, Ø=70 mm; HL-LHC MQX: 4 x 8 m x; Ø=150 mm
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Super conducting magnets beyond 10 tesla of accelerator qualities.
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Technical challenges:Nb3Sn is difficult material
Requires high temperature coil reaction after winding Materials compatibility (coil parts, insulation) Thermal expansion differentials (more critical for long magnets) Need to prevent degradation under stress Progress in Nb3Sn current density rapidly translated in record field dipoles Since ~2003, the critical current density
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Here cryo-collimators could be accomodated For HL-LHC the collimation needs to be improved, but no space is available replace 8T magnets (rather long) by 11 T magnets will gain space for collimation 11T magnets are under development within HL- LHC (in collaboration with Fermilab)
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Ingrid-Maria Gregor, DESY - Challenges at High Lumi LHC
The minimum β* is limited by the aperture of the triplets at the IP and also by the chromatic aberations introduced by the very tight squeeze Small β*⇒huge β at focusing quad Need bigger quads to go to smaller β*
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Existing quads
Proposed for upgrade
⇒ Also beyond the limit of NbTi -> Nb3Sn
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US-LARP is engaged in the production of a model by 2013 (4...6 m length) for the decision on the technology to be used (Nb3Sn vs. Nb-Ti) 120 mm aperture and 200 T/m gradient Testing first 1m long prototype High Field Quadrupole HQ (120 mm aperture, 1 m long) Achieved >155 T/m gradient in first test, at 4.5K Already above NbTi intrinsic limit at 1.9K First quench >150 T/m in second test Several coil failures due to insulation & conductor damage Traced to high compression during coil fabrication New & more challenging design - requires
The Nb3Sn development plan aims at demonstrating readiness for a technology decision and construction initiation in 2014
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SQ SM TQS LR LQS-4m HQ TQC
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see e.g. J.P.Koutchouk, Cham. 2010)
cσ2 z
Three possibilities in LHC, specific to crossing at an angle (no yet decided):
Leveling via dynamic beta* adjustments
no additional hardware necessary, but is probably complex to implement but is cheap.
Leveling via dynamic bunch length adjustments
no or minor side effect if the beam remains stable; needed: reduction of the voltage by 16 + bunch shortening
Leveling via dynamic crossing angle adjustments
Leveling via the Xing angle appears to have the best potential (performance, complexity) but requires unexplored solutions (Crab Crossing) or some interference with detectors (Early Separation). Integrated Lumi is the same
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Increase peak luminosity with increasing x- angle Increase intensities and smaller emittances beyond head-on beam-beam limit Level luminosity (reduce Pile-up, radiation damage)
Ingrid-Maria Gregor, DESY - Challenges at High Lumi LHC
RF crab cavity deflects head and tail in
effectively “head on” for luminosity and tune shift The crab cavity creates two-loop magnetic field (blue) inside to kick bunches sideway. 1st proposed in 1988, in operation at KEKB since 2007
http://www.kek.jp/intra-e/feature/2010/KEKBCrabCavity.html
Example of an crab cavity creating a two-loop magnetic field
Ingrid-Maria Gregor, DESY - Challenges at High Lumi LHC
The challenge: a normal RF cavity requires a transverse dimension > 0.609 λ ! For 400 MHz, this means > 460 mm. The LHC beams are separated 194 mm (0.26 λ)! Something very unconventional is needed!
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Ingrid-Maria Gregor, DESY - Challenges at High Lumi LHC
Parallel bar cavity (ODU) Half wave resonator (SLAC) Four bar cavity (U Lancaster) Kota cavity (KEK)
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Retain a conventional cavity option in the unlikely event of major unforeseen ’show stopper’ with all compacts… Requires significant civil engineering costs due to needed dogleg sections in the IRs Still acceptable, in view of the importance gaining back luminosity from the crossing angle. A straightforward conventional cavity installation in IR 4 as a global scheme would serve as an alternate option in the worst case. Decision point 2015 – stop if Compact CC’s are validated! Cryostat design exists (from LARP) compatible with P4 (800 MHz)
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LHC imposed brightness must be present from the lowest energy because brightness is (at best) conserved in a cascade of proton accelerators (Liouville’s theorem). Brightness (emittance and beam intensity) is defined in the accelerator chain before injection into the LHC. The emittance can be improved by increasing the injection energy It was decided to build a new linear accelerator at the beginning of the chain
Increasing the beam intensity by a factor of 2 Increase injection energy in the PS from 1.4 to 2 GeV, increasing the field in the PSB magnets and replacing its power supply Higher energy out of the PS gives smaller transverse emittance and beam sizes => reducing the injections losses into the SPS
Building etc. already existing
https://indico.cern.ch/conferenceDisplay.py?confId=129870
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⇒ Increase injection energy in the PSB from 50 to 160 MeV, Linac4 (160 MeV H-) to replace Linac2 (50 MeV H+) ⇒ Increase injection energy in the PS from 1.4 to 2 GeV, increasing the field in the PSB magnets, replacing power supply and changing transfer equipment ⇒ Upgrade the PSB , PS and SPS to make them capable to accelerate and manipulate a higher brightness beam (feedbacks, cures against electron clouds, hardware modifications to reduce impedance…)
To increase reliability and lifetime (until ~2030!) (tightly linked with consolidation) ⇒ Upgrade/replace ageing equipment (power supplies, magnets, RF…) ⇒ Procure spares ⇒ Improve radioprotection measures (shielding, ventilation…)
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Linac4 PS injector, PS and SPS Beam characteristics at LHC injection
2011 - 2012
Continuation of construction…
equipment
25 ns, 1.15 1011p/b, >2.9 mm.mrad 50 ns, 1.7 1011p/b, >2.5 mm.mrad 75 ns, 1.2 1011 p/b, ≤ 2 mm.mrad
2013 – 2014
(Long Shutdown 1)
commissioning
prototypes in PS and SPS
2015 - 2017
Linac4 beam current
increase of PSB brightness
(Injection still at 1.4 GeV)
PS injector, PS and SPS
PS and SPS hardware upgrades)
2018
(Long Shutdown 2)
PS and SPS
2019 –2021
After ~1 year of operation: beam characteristics for HL-LHC…
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Ingrid-Maria Gregor, DESY - Challenges at High Lumi LHC
Total beam current. Limited by:
Reduce β*, limited by
Brightness, limited by
Geometric factor, related to crossing angle and bunch length Maximize number of bunches
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Booster energy upgrade 1.4 → 2 GeV, ~2014
SPS enhancements 2012-2022
Ingrid-Maria Gregor, DESY - Challenges at High Lumi LHC
Leveled peak luminosity: L = 5 1034 cm-2 sec-1 Virtual peak luminosity: L = 10 1034 cm-2 sec-1 Integrated luminosity: 200 fb-1 to 300 fb-1 per year Total integrated luminosity: ca. 3000 fb-1
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Ingrid-Maria Gregor, DESY - Challenges at High Lumi LHC
The LHC is running extremely good, the goal for 2011 to collect 1 fb-1 was already reached -> nex goal is 5 fb-1 An even more potent machine is envisaged for 2020+ to access rare decays R&D for this goal is in full swing, a good understanding of the current machine allows to plan for the future 5*1034 is a possible luminosity for HL-LHC
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2008 by Lars Ottesen Henriksen
Ingrid-Maria Gregor, DESY - Challenges at High Lumi LHC
This talk represents the work of an almost countless number of people. I have incorporated significant material from:
The annual Chamonix meetings http://tinyurl.com/Chamonix2011 Frank Zimmermann’s many luminosity talks, Talks presented at LARP collaborations and DOE reviews See http://www.uslarp.org/
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Accelerator Physics in general:
Klaus Wille, “The Physics of Particle Accelerators”, Oxford University Press, 2000 CERN Accelerator School:http://cdsweb.cern.ch/record/603056/files/ CERN-2006-002.pdf Fundamentals of Accelerator Physics and Technology: http://uspas.fnal.gov/ materials/09UNM/UNMFund.html
HL-LHC Upgrade Details Breaching the Phase I Optics Limitations for the HL-LHC, S. Fartoukh
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ie, sector 3-4 goes from point 3 to point 4
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Compact Muon Solenoid (CMS) A Toroidal LHC ApparatuS (ATLAS) A Large Ion Collider Experiment (ALICE) B physics at the LHC (LHCb)
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Cryogenics is complicated and expensive, so what is the interest
High current density
Larger ampere-turns in a small volume -> no need for iron (but iron is still useful for shielding) Reduced power consumption
Superconductivity opens up new technical possibilities
Higher magnetic fields -> increased bending power
Higher electric fields -> higher accelerating gradients
Higher quadrupole gradients ! more focusing power
Ingrid-Maria Gregor, DESY - Challenges at High Lumi LHC
Ideal scenario: no imperfections included!
Chamonix 2011
Ingrid-Maria Gregor, DESY - Challenges at High Lumi LHC
Photoelectrons created in the vacuum pipe are accelerated by passing proton bunches. Slow or reflected secondary electrons survive until the next bunch arrives Depending on the pipe surface conditions and bunch spacing this may lead to an electron cloud build-up Effects on stability, emittance growth etc. are the consequence Currently the LHC is running at 50ns bunch spacing to reduce this effect
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Main Technical question
Space constraints -> 800 MHz elliptical (simple) versus 400 MHz “exotic”
Jc(4.2 K, 6 Jc(1.9 K, 9
T(K) B(T) J(A/mm2) 49:(;( ;9<3&#=( ;9!3:(=(
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The superconducting state only
temperature, magnetic field and transport current density Superconducting magnets produce high field with high current density Lowering the temperature enables better usage of the superconductor, by broadening its working range
Jc(4.2 K, 6 T)2300 A/mm2 Jc(1.9 K, 9 T)2300 A/mm2
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Hour glass effect
Relevant when β* is decreased
close to the bunch length σz. Define r = β* / σz . Luminosity gets reduced. For round beams the factor is
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Ingrid-Maria Gregor, DESY - Challenges at High Lumi LHC
Two crossing beams see the field of each other Space charge cancellation not present anymore Important limitation for high luminosity Beam beam effects: considered to be a major challenge to reach LHC luminosity
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witness bunches (zero collisions);
bunches colliding in IP 1 5 and 2 (3 collisions);
bunches colliding in IP 1 5 and 8 (3 collisions);
bunches colliding in IP 2 and 8 (2 collisions).
Effects of the beam-beam force are visible on the lifetime of the various bunches.
Beams in collision Beams in collision Beam1 Beam2
Intensity loss (%)
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Total crossing angle of 300 µrad Beam size at IP 16 µm, in arcs about 1 m Beams in the arcs in two vacuum chambers
1232 dipole magnets. B field 8.3 T (11.8 kA) @ 1.9 K (super-fluid Helium) 2 magnets-in-one design : two beam tubes with an
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Operating challenges:
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Extraction kickers Dilution kickers Extraction septum magnets Dump block Complex beam dumping system
commissioned. Beam swept over dump surface (power load)
Ingrid-Maria Gregor, DESY - Challenges at High Lumi LHC
[fromWikipedia] “CERN operates a network of six accelerators and a decelerator. Each machine in the chain increases the energy of particle beams before delivering them to experiments or to the next more powerful accelerator…
All these accelerators are used to prepare the beam needed by the Large Hadron Collider
Two linear accelerators generate low energy particles. Linac2 accelerates protons to 50MeV for injection in to the Proton Synchrotron Booster (PSB), and Linac3 provides heavy ions at 4.2MeVu fori injection into the Low Energy Ion Ring (LEIR).
The Proton Synchrotron Booster increases the energy of particles generated by the proton linear accelerator
before they are transferred to the other accelerators. The Low Energy Ion Ring (LEIR) accelerates the ions from the ion linear accelerator, before transferring them to the Proton Synchrotron (PS). This accelerator was commissioned in 2005, after having been reconfigured from the previous Low Energy Antiproton Ring (LEAR). The 28GeV Proton Synchrotron (PS), built in 1959 and still operating as a feeder to the more powerful SPS. The Super Proton Synchrotron (SPS), a circular accelerator with a diameter of 2 kilometres built in a tunnel, which started operation in 1976. It was designed to deliver an energy of 300GeV and was gradually upgraded to 450GeV. As well as having its own beamlines for fixed-target experiments (currently COMPASS and NA62),it has been operated as a proton– antiproton collider (the SppS collider), and for accelerating high energy electrons and positrons which were injected into the Large Electron Positron Collider (LEP). Since2008, it has been used to inject protons and heavy ions into the Large Hadron Collider LHC). 67