Rüdiger Schmidt - Dezember The LHC accelerator Rüdiger Schmidt - CERN Besuch 2/12/2006 Challenges Particle physics LHC accelerator physics LHC technology Operation and machine protection Cryogenic distribution line

Rüdiger Schmidt - Dezember Energy and Luminosity l Particle physics requires an accelerator colliding beams with a centre-of-mass energy substantially exceeding 1TeV l In order to observe rare events, the luminosity should be in the order of [cm -1 s -2 ] (challenge for the LHC accelerator) l Event rate: l Assuming a total cross section of about 100 mbarn for pp collisions, the event rate for this luminosity is in the order of 10 9 events/second (challenge for the LHC experiments) l Nuclear and particle physics require heavy ion collisions in the LHC (quark-gluon plasma.... )

Rüdiger Schmidt - Dezember CERN and the LHC

CERN is the leading European institute for particle physics It is close to Geneva across the French Swiss border There are 20 CERN member states, 5 observer states, and many other states participating in research LHC CMS ATLAS

LEP: e+e- 104 GeV/c ( ) Circumference 26.8 km LHC proton-proton Collider 7 TeV/c in the LEP tunnel 2 rings Injection from SPS at 450 GeV/c ATLAS CMS

Rüdiger Schmidt - Dezember 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 2002 : LEP equipment removed 2003 : Start of the LHC installation 2005 : Start of hardware commissioning 2007 : Commissioning with beam planned

Rüdiger Schmidt - Dezember LHC Accelerator Physics: An Introduction Why protons? Why in the LEP tunnel? Why superconducting magnets? Why “two” accelerators in one tunnel?

Rüdiger Schmidt - Dezember Particle acceleration Acceleration of a charged particle by an electrical potential Energy gain given by the potential l For an acceleration to 7 TeV a voltage of 7 TV is required l The maximum electrical field in an accelerator is in the order of some 10 MV/m (superconducting RF cavities) l To accelerate to 7 TeV would require a linear accelerator with a length of about 350 km (assuming 20 MV/m)

Rüdiger Schmidt - Dezember How to get to 7 TeV: Synchrotron – circular accelerator and many passages in RF cavities LINAC (planned for several hundred GeV - but not above 1 TeV) LHC circular machine with energy gain per turn some MeV

Rüdiger Schmidt - Dezember Particle deflection: Lorentz Force The force on a charged particle is proportional to the charge, and to the vector product of velocity and magnetic field: Maximaler Impuls 7000 GeV/c Radius 2805 m Ablenkfeld B = 8.33 Tesla Magnetfeld mit Eisenmagneten maximal 2 tesla, daher werden supraleitende Magnete benötigt z x s v B F

Rüdiger Schmidt - Dezember LHC Layout eight arcs (sectors) eight long straight section (about 700 m long) IR6: Beam dumping system IR4: RF + Beam instrumentation IR5:CMS IR1: ATLAS IR8: LHC-B IR2:ALICE Injection IR3: Momentum Cleaning (warm) IR7: Betatron Cleaning (warm) Beam dump blocks

Rüdiger Schmidt - Dezember Autumn 2004 The CERN accelerator complex: injectors and transfer High intensity beam from the SPS into LHC at 450 GeV via TI2 and TI8 LHC accelerates to 7 TeV LEIR CPS SPS Booster LINACS LHC TI8 TI2 Ions protons Beam 1 Beam 2 Beam size of protons decreases with energy:  2 = 1 / E Beam size large at injection Beam fills vacuum chamber at 450 GeV

Rüdiger Schmidt - Dezember Beam transport Need for keeping protons on a circle: dipole magnets Need for focusing the beams: l Particles with different injection parameters (angle, position) separate with time Assuming an angle difference of rad, two particles would separate by 1 m after 10 6 m. At the LHC, with a length of m, this would be the case after 50 turns (5 ms !) l The beam size must be well controlled At the collision point the beam size must be tiny l Particles with (slightly) different energies should stay together l Particles would „drop“ due to gravitation

Rüdiger Schmidt - Dezember The LHC arcs: FODO cells u Dipole- und Quadrupol magnets –Particle trajectory stable for particles with nominal momentum u Sextupole magnets –To correct the trajectories for off momentum particles –Particle trajectories stable for small amplitudes (about 10 mm) u Multipole-corrector magnets –Sextupole - and decapole corrector magnets at end of dipoles –Particle trajectories can become instable after many turns (even after, say, 10 6 turns)

Rüdiger Schmidt - Dezember High luminosity by colliding trains of bunches Number of „New Particles“ per unit of time: The objective for the LHC as proton – proton collider is a luminosity of about [cm -1 s -2 ] LEP (e+e-) : [cm -1 s -2 ] Tevatron (p-pbar) : [cm -1 s -2 ] B-Factories: [cm -1 s -2 ]

Rüdiger Schmidt - Dezember Luminosity parameters

Rüdiger Schmidt - Dezember Beam beam interaction determines parameters Number of protons N per bunch limited to about f = Hz Beam size σ = 16  m for  = 0.5 m with one bunch N b =1 with N b = 2808 bunches (every 25 ns one bunch) L = [cm -2 s -1 ]

Rüdiger Schmidt - Dezember Large number of bunches IP l Crossing angle to avoid parasitic beam beam interaction

Rüdiger Schmidt - Dezember Large number of bunches IP l Crossing angle to avoid parasitic beam beam interaction

Rüdiger Schmidt - Dezember summarising constraints and consequences…. Centre-of-mass energy must well exceed 1 TeV, LHC installed into LEP tunnel l Colliding protons, and also heavy ions l Magnetic field of 8.3 T with superconducting magnets l Large amount of energy stored in magnets Luminosity of cm -2 s -1 l Need for “two accelerators” in one tunnel with beam parameters pushed to the extreme – with opposite magnetic dipole field l Large amount of energy stored in beams

Rüdiger Schmidt - Dezember Very high beam current Many bunches and high energy - Energy stored in one beam about 360 MJ l Dumping the beam in a safe way l Beam induced quenches (when of beam hits magnet at 7 TeV) l Beam cleaning (Betatron and momentum cleaning)

Livingston type plot: Energy stored in the beam courtesy R.Assmann Transverse energy density: even a factor of 1000 larger

Rüdiger Schmidt - Dezember LHC accelerator in the tunnel LHC Main Systems Superconducting magnets Cryogenics Vacuum system Powering (industrial use of High Temperature Superconducting material)

Rüdiger Schmidt - Dezember main dipoles multipole corrector magnets 392 main quadrupoles corrector magnets Regular arc: Magnets

Rüdiger Schmidt - Dezember Regular arc: Cryogenics Supply and recovery of helium with 26 km long cryogenic distribution line Static bath of superfluid helium at 1.9 K in cooling loops of 110 m length Connection via service module and jumper

Rüdiger Schmidt - Dezember Insulation vacuum for the cryogenic distribution line Regular arc: Vacuum Insulation vacuum for the magnet cryostats Beam vacuum for Beam 1 + Beam 2

Rüdiger Schmidt - Dezember Regular arc: Electronics Along the arc about several thousand electronic crates (radiation tolerant) for: quench protection, power converters for orbit correctors and instrumentation (beam, vacuum + cryogenics)

R.Schmidt – CERN visit 2/12/ Transfer on jacks

R.Schmidt – CERN visit 2/12/ Preparation of interconnect

R.Schmidt – CERN visit 2/12/ Interconnection of beam tubes Cryogenic distribution line

Rüdiger Schmidt - Dezember ATLAS Detector

R.Schmidt – CERN visit 2/12/ LHC low-  triplets (installed in IR5)

R.Schmidt – CERN visit 2/12/ LHC low-  triplets ( Q1 installed in IR5)

R.Schmidt – CERN visit 2/12/ Getting 13 kA into the cold….

R.Schmidt – CERN visit 2/12/ Getting beam into LHC…

R.Schmidt – CERN visit 2/12/ Getting beam into LHC… TI8 to LHC

R.Schmidt – CERN visit 2/12/ Getting beam into LHC… injection kicker

Rüdiger Schmidt - Dezember Dipolmagnets Length about 15 m Magnetic Field 8.3 T Two beam tubes with an opening of 56 mm Dipole magnets for the LHC

Rüdiger Schmidt - Dezember Coils for Dipolmagnets 15 m long

Rüdiger Schmidt - Dezember Superconducting cable for 12 kA 15 mm / 2 mm Temperature 1.9 K cooled with Helium Force on the cable: F = B * I0 * L with B = 8.33 T I0 = Ampere L = 15 m F = 165 tons 56 mm

Rüdiger Schmidt - Dezember Beam tubes Supraconducting coil Nonmagetic collars Ferromagnetic iron Steelcylinder for Helium Insulationvacuum Supports Vacuumtank

Rüdiger Schmidt - Dezember First cryodipole lowered on 7 March 2005 Only one access point for 15 m long dipoles, 35 tons each

Rüdiger Schmidt - Dezember Transport in the tunnel with an optical guided vehicle about 1600 magnets to be transported for 15 km at 3 km/hour

Rüdiger Schmidt - Dezember Machine protection

Rüdiger Schmidt - Dezember Kugelstossen: The energy of one shot (5 kg) at 800 km/hour corresponds to the energy stored in one bunch at 7 TeV. There are 2808 bunches. Factor 200 compared to HERA, TEVATRON and SPS. shot Energy stored in one beam at 7 TeV: 362 MJoule

Rüdiger Schmidt - Dezember 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 6 cm 25 cm 0.1 % of the full LHC beams V.Kain et al

Rüdiger Schmidt - Dezember 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

Rüdiger Schmidt - Dezember 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

Rüdiger Schmidt - Dezember Beam Dump Block - Layout about 8 m L.Bruno concrete shielding beam absorber (graphite)

Rüdiger Schmidt - Dezember Beam on Beam Dump Block about 35 cm M.Gyr initial transverse beam dimension in the LHC about 1 mm beam is blown up due to long distance to beam dump block additional blow up due to fast dilution kickers: painting of beam on beam dump block beam impact within less than 0.1 ms

Rüdiger Schmidt - Dezember Protection and Beam Energy A small fraction of beam sufficient for damage Very efficient protection systems throughout the cycle are required A tiny fraction of the beam is sufficient to quench a magnet Very efficient beam cleaning is required Sophisticated beam cleaning with about 50 collimators, each with two jaws, in total about 90 collimators and beam absorbers Collimators are close to the beam (full gap as small as 2.2 mm, for 7 TeV with fully squeezed beams), particles will always touch collimators first !

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

Rüdiger Schmidt - Dezember 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

Rüdiger Schmidt - Dezember 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

Rüdiger Schmidt - Dezember First collimator in the tunnel

Rüdiger Schmidt - Dezember RF contacts for guiding image currents Beam spot 2 mm

Rüdiger Schmidt - Dezember Conclusions

Rüdiger Schmidt - Dezember Recalling LHC challenges 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

Rüdiger Schmidt - Dezember 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

Rüdiger Schmidt - Dezember Some references Accelerator physics l Proceedings of CERN ACCELERATOR SCHOOL (CAS), In particular: 5th General CERN Accelerator School, CERN 94-01, 26 January 1994, 2 Volumes, edited by S.Turner Superconducting magnets / cryogenics l Superconducting Accelerator Magnets, K.H.Mess, P.Schmüser, S.Wolff, World Scientific 1996 l Superconducting Magnets, M.Wilson, Oxford Press l Superconducting Magnets for Accelerators and Detectors, L.Rossi, CERN-AT MAS (2003) LHC l Technological challenges for the LHC, CERN Academic Training, 5 Lectures, March 2003 (CERN WEB site) l Beam Physics at LHC, L.Evans, CERN-LHC Project Report 635, 2003 l Status of LHC, R.Schmidt, CERN-LHC Project Report 569, 2003 l...collimation system.., R.Assmann et al., CERN-LHC Project Report 640, 2003 l LHC Design Report 1995 l LHC Design Report in preparation