R.Schmidt - AAPT The LHC Accelerator and (some of) its Challenges The LHC Accelerator and (some of) its Challenges Rüdiger Schmidt - CERN AAPT Baltimore January 2008 The LHC and the relativistic hammer thrower Acceleration and Deflection High intensity beams at very high energy The LHC accelerator complex Operation und Machine Protection Status and Outlook

R.Schmidt - AAPT CERN: leading European institute for Particle Physics, started 1954 with 2600 staff and 6800 users Close to Geneva across the French-Swiss border 20 member states, ~7 observers (e.g. USA), many others participating LEP / LHC The U.S. LHC Accelerator Research Program (LARP) is a collaboration of BNL, FNAL, LBNL, and SLAC, working with CERN to address a variety of issues.

R.Schmidt - AAPT LHC: Energy and Luminosity l Particle physics requires an accelerator colliding beams with a centre-of-mass energy substantially exceeding 1TeV l To observe rare events, the luminosity should be in the order of [cm -2 s -1 ] (challenge for the LHC accelerator) l Event rate: l Nuclear and particle physics require heavy ion collisions in the LHC (quark-gluon plasma.... )

R.Schmidt - AAPT CERN accelerator complex LEP e+e- ( ) 104 GeV/c Tunnel with a Circumference of 26.8 km LHC proton proton beams colliding in 4 points at 7 TeV/c Ion collisions also planned CERN Main site Switzerland Lake Geneva France LHC Accelerator (about 100m underground) SPS accelerator CERN Prevessin site CMS ALICELHCbATLAS

R.Schmidt - AAPT LHC: From first ideas to realisation 1982 : First studies for the LHC project 1983 : Z0 detected at SPS proton antiproton collider 1985 : Nobel Price for S. van der Meer and C. Rubbia 1989 : Start of LEP operation (Z-factory) 1994 : Approval of the LHC by the CERN Council 1996 : Final decision to start the LHC construction 1996 : LEP operation at 100 GeV (W-factory) 2000 : End of LEP operation and removal of LEP equipment 2003 : Start of the LHC installation 2005 : Start of hardware commissioning 2007 : Installation of superconducting magnets finished 2008 : Beam commissioning and first collisions planned

R.Schmidt - AAPT The LHC: just another collider? NameStartParticlesMax proton energy [GeV] Length [m] B Field [Tesla] Stored beam energy [MJoule] TEVATRON Fermilab Illinois USA 1983p-pbar for protons HERA DESY Hamburg Germany 1992p – e+ p – e for protons RHIC Brookhaven Long Island USA 2000Ion-Ion p-p per proton beam LHC CERN Geneva Switzerland 2008Ion-Ion p-p per proton beam

R.Schmidt - AAPT To accelerate protons to 7 TeV … Acceleration of the protons in an electrical field with 7000 Billion Volt……. But:  no constant electrical field above some Million Volt (break down)  no time dependent electrical field above some 10 Million Volt Proton travel around the circular accelerator with the speed of light and are accelerated by ~1 Million Volt per turn

R.Schmidt - AAPT ….and to keep them on the circle The relativistic hammer thrower Magnets deflect protons and keep them on a circle Electrical field accelerates proton and magnetic field increases Very strong magnetic field

R.Schmidt - AAPT Lorentz force on a charged particle: acceleration The force on a charged particle is proportional to the charge, the electric field, and the vector product of velocity and magnetic field: x s v E FEFE Electric field about 10 MV z

R.Schmidt - AAPT Lorentz force on a charged particle: acceleration and deflection The force on a charged particle is proportional to the charge, the electric field, and the vector product of velocity and magnetic field: z x s B FBFB Electric field about 10 MV Momentum 7000 GeV/c Radius 2805 m Magnetic field B = 8.3 Tesla Superconducting magnets required operating at 1.9 K Deflecting magnetic fields for two beams in opposite directions v

R.Schmidt - AAPT A total number of 1232 dipole magnets, 15 m long, are required to close the m long circle

R.Schmidt - AAPT LHC dipole magnet lowered into the tunnel First cryodipole lowered on 7 March 2005 Descent of the last magnet, 26 April 2007

R.Schmidt - AAPT Interconnecting two magnets out of 1700

R.Schmidt - AAPT Principle of LHC dipole magnets Two beam tubes Total current per aperture in one direction about 1 MA Proton beam 1 Proton beam 2

R.Schmidt - AAPT Dipole magnet cross section Steelcylinder for pressurised helium Beam tubes (56 mm)Superconducting coil Vacuumtank Insulationvacuum Nonmagnetic collars Support posts Ferromagnetic iron16 mBar cooling tube

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R.Schmidt - AAPT The superconducting state only occurs in a limited domain of 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 LHC dipole magnets operate in helium at a temperature of 1.9 K Outside the domain the magnet quenches – mJ are sufficient to locally heat the superconductor T [K] B [T] J [kA/mm 2 ] Operating temperature of NbTi superconductors J [kA/mm2]

R.Schmidt - AAPT RF cavities, four per beam with some 10 MVolt

R.Schmidt - AAPT High intensity beams at very high energy

R.Schmidt - AAPT ~40 m in straight section (not to scale) Experiment Luminosity parameters

R.Schmidt - AAPT Beam beam interaction determines parameters Number of protons N per bunch limited to about f = Hz Beam size at IP σ = 16  m for  = 0.5 m (beam size in arc σ = ~ 0.2 mm with one bunch N b =1 with N b = 2808 bunches (every 25 ns one bunch) L = [cm -2 s -1 ] => 362 MJoule per beam

R.Schmidt - AAPT Challenges for LHC l High-field (8.3 Tesla) superconducting magnets operating at 1.9 K with 10 GJ stored energy in the magnets l Beam-parameters pushed to the extreme l Energy stored in the beam two orders of magnitude above other machines l GJoule beams running through superconducting magnets that quench with mJoule l Complexity of the accelerator (likely to be the most complex scientific instrument ever constructed) with ~10000 magnets powered in ~1700 electrical circuits The energy stored in one LHC beam corresponds approximately to: 90kg TNT 8kg gasoline 15kg chocolate

R.Schmidt - AAPT The LHC accelerator complex

R.Schmidt - AAPT LHC Layout eight arcs (sectors) eight long straight section (about 700 m long) IR6: Beam extraction and dump IR4: RF + Beam instrumentation IR5:CMS IR1: ATLAS IR8: LHC-B IR2:ALICE Injection IR3: Momentum beam cleaning (warm) IR7: Betatron beam cleaning (warm) Beam dump blocks

R.Schmidt - AAPT TI 8 LHC SPS 6911 m 450 GeV LSS6 IR2 TT40 LSS4 IR8 TI 8 beam tests 23/ / TI 2 beam test 28/ combined length 5.6 km over 700 magnets ca. 2/3 of SPS LHC transfer lines and injections - overview TT40 beam tests TI 2

R.Schmidt - AAPT Transfer line TI8 (MIBT magnet)

R.Schmidt - AAPT ATLAS Detector

R.Schmidt - AAPT Focusing beam to a size of 16  m High gradient quadrupole magnet triplet with large aperture (US-JAPAN) Total crossing angle of 300  rad Beam size at interaction point 16  m, in arcs about 0.3 mm Collisions in multibunch operation distance about 100 m Interaction point QFQDQFQDQFQD Experiment

R.Schmidt - AAPT One of the triplets at Point 5 (CMS)

R.Schmidt - AAPT Operation and machine protection

R.Schmidt - AAPT injection phase 12 batches from the SPS (every 20 sec) one batch 216 / 288 bunches LHC magnetic cycle - beam injection L.Bottura 450 GeV 7 TeV beam dump energy ramp coast start of the ramp

R.Schmidt - AAPT What happens in case the full LHC beam impact onto material?

R.Schmidt - AAPT Full LHC beam deflected into copper target Target length [cm] vaporisation melting N.Tahir (GSI) et al. Copper target 2 m Energy density [GeV/cm 3 ] on target axis 2808 bunches Beam could tunnel for ~30 m into target

R.Schmidt - AAPT SPS experiment: Beam damage at 450 GeV Controlled SPS experiment l 8  protons clear damage l beam size σ x/y = 1.1mm/0.6mm above damage limit l 2  protons below damage limit 25 cm 0.1 % of the full LHC beam energy 10 times the cross section 6 cm 8     10 12

R.Schmidt - AAPT The only component that can stand a loss of the full beam is the beam dump block all other components would be damaged about 8 m concrete shielding beam absorber (graphite) about 35 cm max C

R.Schmidt - AAPT Beam Cleaning System Primary collimator Secondary collimators Absorbers Protection devices Tertiary collimators Triplet magnets Beam Primary halo particle Secondary halo Tertiary halo + hadronic showers hadronic showers Beam cleaning (collimation) system capture particles that would be lost in superconducting magnets and induce quenches and damage More than 100 collimators jaws needed for the LHC beam Most collimators made of carbon to survive severe beam impact! Collimators must be precisely aligned (< 0.1 mm) to guarantee a high efficiency above 99.9% at nominal intensities. It’s not easy to stop 7 TeV protons !! Experiment

R.Schmidt - AAPT RF contacts for guiding image currents Beam spot Carbon jaw 1.2 m long ~2 mm

R.Schmidt - AAPT Status and Outlook

R.Schmidt - AAPT Status summary l Installation and magnet interconnections finished l Cryogenics Nearly finished and operational (e.g. cryoplants) l Powering system: commissioning on the way Power converters commissioning on short circuits in tunnel finished Magnet powering tests started in two sectors l Other systems (RF, Beam injection and extraction, Beam instrumentation, Collimation, Interlocks, Controls) l Injector complex and transfer lines ready l In May / June ready for first beam l Some months later first luminosity operation… …..if there are no problems that require partial warm-up

R.Schmidt - AAPT Magnet temperature in one 3 km long sector Two-In-One superconducting magnets inside 1.9 K system

R.Schmidt - AAPT Ramping the dipole magnets to a current for 5 TeV High current power converters controlling the current with an unprecedented accuracy of 1 ppm 8000 A 4000 A Dipole magnet current 12 hours

R.Schmidt - AAPT Current leads with High Temperature Superconductors at an industrial scalce 42 Feedboxes (‘DFB’) : transition from copper cable to super-conductor Water cooled Cu cables

R.Schmidt - AAPT DFB with ~17 out of 1600 HTS current leads

R.Schmidt - AAPT stages 1st stage cartridge Air Liquide & IHI-Linde Axial-centrifugal impeller Cold compressors of LHC 1.8 K units to provide helium at 1.9 K

R.Schmidt - AAPT First collimator in the tunnel R.Assmann et al Vacuum tank with two jaws installed Advanced Carbon Composite material for the jaws with water cooling! Designed for maximum robustness: Advanced Carbon Composite material for the jaws with water cooling!

R.Schmidt - AAPT Always smooth progress? No ….. this is unrealistic l The LHC is a machine with unprecedented complexity l The technology is pushed to its limits l The LHC is a ONE-OFF machine l The LHC was constructed during a period when CERN had to substantially reduce the personel l Problems came up and were solved / are being solved, such as dipole magnets, cryogenics distribution line, collimators, inner triplet, RF fingers (PiMS), He level gauges, …. In my view what makes such project a success: not absence of problems, but because problems are detected and adressed with competent and dedicated staff and collaborators that master all different technologies

R.Schmidt - AAPT Conclusions l The LHC is a global project with the world-wide high- energy physics community devoted to its progress and results l As a project, it is much more complex and diversified than the SPS or LEP or any other large accelerator project constructed to date Machine Advisory Committee, chaired by Prof. M. Tigner, March 2002 l No one has any doubt that it will be a great challenge for both machine to reach design luminosity and for the detectors to swallow it l However, we have a competent and experienced team, and 30 years of accumulated knowledge from previous CERN projects has been put into the LHC design L.Evans (LHC Project Leader)

R.Schmidt - AAPT The LHC accelerator is being realised by CERN in collaboration with institutes from many countries over a period of more than 20 years Main contribution come from USA (via LARP) and from other countries (Japan, Russia, India, Canada, special contributions from France and Switzerland) Industry plays a major role in the construction of the LHC Thanks for the material from: R.Assmann, R.Bailey, F.Bordry, L.Bottura, L.Bruno, L.Evans, B.Goddard, M.Gyr, Ph.Lebrun Acknowledgement see also P.Limons (FERMILAB) LHC talk tomorrow

R.Schmidt - AAPT Reserve Slides

R.Schmidt - AAPT orthogonal g 2a z LHC RF frequency 400 MHz Revolution frequency Hz Particle acceleration: RF cavity with electric field

R.Schmidt - AAPT Schematic layout of beam dump system in IR6 Q5R Q4R Q4L Q5L Beam 2 Beam 1 Beam Dump Block Septum magnet deflecting the extracted beam H-V kicker for painting the beam about 700 m about 500 m Fast kicker magnet

R.Schmidt - AAPT Beam losses into material l Proton losses lead to particle cascades in materials l The energy deposition leads to a temperature increase l For the maximum energy deposition as a function of material there is no straightforward expression l Programs such as FLUKA are being used for the calculation of the energy deposition Magnets could quench….. beam lost - re-establish condition will take hours The material could be damaged….. melting losing their performance (mechanical strength) Repair could take several weeks

R.Schmidt - AAPT Operational margin of a superconducting magnet Bc Tc 9 K Applied Magnetic Field [T] Bc critical field 1.9 K quench with fast loss of ~5 · 10 9 protons quench with fast loss of ~5 · 10 6 protons 8.3 T 0.54 T QUENCH Tc critical temperature This is about 1000 times more critical than for TEVATRON, HERA, RHIC Temperature [K] Applied magnetic field [T]

R.Schmidt - AAPT Quench - transition from superconducting state to normalconducting state Quenches are initiated by an energy in the order of mJ (corresponds to the energy of 1000 protons at 7 TeV) l Movement of the superconductor by several  m (friction and heat dissipation) l Beam losses l Failure in cooling To limit the temperature increase after a quench (in 1s to 5000 K) l The quench has to be detected l The energy is distributed in the magnet by force-quenching the coils using quench heaters l The magnet current has to be switched off within << 1 second

R.Schmidt - AAPT Courtesy F.Bordry 2ppm Current tracking between three main circuits

R.Schmidt - AAPT

R.Schmidt - AAPT Beam lifetime with nominal intensity at 7 TeV Beam lifetime Beam power into equipment (1 beam) Comments 100 h1 kWHealthy operation 10 h10 kWOperation acceptable, collimation must absorb large fraction of beam energy (approximately beam losses = cryogenic cooling power at 1.9 K) 0.2 h500 kWOperation only possibly for short time, collimators must be very efficient 1 min6 MWEquipment or operation failure - operation not possible - beam must be dumped << 1 min> 6 MWBeam must be dumped VERY FAST Failures will be a part of the regular operation and MUST be anticipated

R.Schmidt - AAPT End of data taking in normal operation: Beam Dump l Luminosity lifetime estimated to be approximately 10 h (after 10 hours only 1/3 of initial luminosity) l Beam current somewhat reduced - but not much l Energy per beam still about MJ l Beams are extracted into beam dump blocks l The only component that can stand a loss of the full beam is the beam dump block - all other components would be damaged l At 7 TeV, fast beam loss with an intensity of about 5% of one single “nominal bunch” could damage superconducting coils l In case of failure: beam must go into beam dump block

R.Schmidt - AAPT Density change in target after impact of 100 bunches Energy deposition calculations using FLUKA Numerical simulations of the hydrodynamic and thermodynamic response of the target with two- dimensional hydrodynamic computer code Target radial coordinate [cm] radial copper solid state N.Tahir (GSI) et al. 100 bunches – target density reduced to 10%

R.Schmidt - AAPT  ~1.3 mm Beam +/- 3 sigma 56.0 mm Beam in vacuum chamber with beam screen at 7 TeV

R.Schmidt - AAPT Beam+/- 3 sigma 56.0 mm 1 mm +/- 8 sigma = 4.0 mm Example: Setting of collimators at 7 TeV - with luminosity optics Beam must always touch collimators first ! R.Assmanns EURO Collimators at 7 TeV, squeezed optics

R.Schmidt - AAPT The LHC Phase 1 Collimator Vacuum tank with two jaws installed Designed for maximum robustness: Advanced Carbon Composite material for the jaws with water cooling! R.Assmann et al

R.Schmidt - AAPT New approaches and novel technologies l Two-In-One superconducting magnets inside 1.9 K system l Compressors operating at cold to provide helium at 1.9 K l Beam screen inside vacuum chamber at higher temperature l High Temperature Superconductors at an industrial scale, for current leads l High current power converters and control of the current with an unprecedented accuracy of 1 ppm l New devices and materials for absorbing the particles l Overall consideration for machine protection: an accidental release of the energy can lead to massive damage

R.Schmidt - AAPT Recalling LHC challenges and outlook l Enormous amount of equipment l Complexity of the LHC accelerator l New challenges in accelerator physics with LHC beam parameters pushed to the extreme Fabrication of equipment Installation LHC Beam commissioning LHC “hardware” commissioning

R.Schmidt - AAPT Repair of the inner triplett

R.Schmidt - AAPT RF bellows in the 1700 interconnections

R.Schmidt - AAPT Arc plug-in module at warm temperature

R.Schmidt - AAPT Arc plug-in module at working temperature

R.Schmidt - AAPT Solution is on the way… l Problem: fingers bend into beampipe obstructing the aperture l Due to wrong angle of RF fingers PLUS size of the gap between the magnet apertures larger than nominal (still inside specification) l Laboratory tests and finite element analysis confirm the two factors l Only part of the interconnects is affected l Complete survey of sector 78 using X-ray techniques l Repair is not so difficult…once bad PiM identified l A technique was developed for quickly checking at warm the LHC beam aperture l Using air flow blowing a light ball equipped with a 40MHz transmitter through the beam vacuum pipe, use BPMs to detect it as it passes