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Der LHC Beschleuniger Rüdiger Schmidt - CERN Vorlesung an der Technische Universität Darmstadt 20 -24 Februar 2006 Herausforderungen LHC Beschleunigerphysik LHC Technologie Operation und Maschinenschutz Rüdiger Schmidt - Februar 2006 - TU Darmstadt Cryogenic distribution line 1

Energy and Luminosity l Particle physics requires an accelerator colliding beams with a centre-of-mass energy substantially exceeding 1 Te. V l In order to observe rare events, the luminosity should be in the order of 1034 [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 109 events/second (challenge for the LHC experiments) l Nuclear and particle physics require heavy ion collisions in the LHC (quark-gluon plasma. . ) Rüdiger Schmidt - Februar 2006 - TU Darmstadt 2

LHC Event 109 events / second Rüdiger Schmidt - Februar 2006 - TU Darmstadt 3

CMS Detektor Rüdiger Schmidt - Februar 2006 - TU Darmstadt 4

ATLAS Detektor Rüdiger Schmidt - Februar 2006 - TU Darmstadt 5

CERN and the LHC Rüdiger Schmidt - Februar 2006 - TU Darmstadt 6

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 CMS LHC ATLAS Rüdiger Schmidt - Februar 2006 - TU Darmstadt 7

LEP: e+e 104 Ge. V/c (1989 -2000) CMS Circumference 26. 8 km LHC proton-proton Collider 7 Te. V/c in the LEP tunnel 2 rings Injection from SPS at 450 Ge. V/c ATLAS Rüdiger Schmidt - Februar 2006 - TU Darmstadt 8

LHC: From first ideas to realisation 1982 : First studies for the LHC project 1983 : Z 0 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 Ge. V (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 - Februar 2006 - TU Darmstadt 9

LHC Accelerator Physics: An Introduction Why protons? Why in the LEP tunnel? Why superconducting magnets? Why “two” accelerators in one tunnel? Rüdiger Schmidt - Februar 2006 - TU Darmstadt 10

Particle acceleration Acceleration of a charged particle by an electrical potential Energy gain given by the potential l For an acceleration to 7 Te. V a voltage of 7 TV is required The maximum electrical field in an accelerator is in the order of some 10 MV/m (superconducting RF cavities) To accelerate to 7 Te. V would require a linear accelerator with a length of about 350 km (assuming 20 MV/m) Rüdiger Schmidt - Februar 2006 - TU Darmstadt 11

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: z s B v F • • x Maximaler Impuls 7000 Ge. V/c Radius 2805 m Ablenkfeld B = 8. 33 Tesla Magnetfeld mit Eisenmagneten maximal 2 tesla, daher werden supraleitende Magnete benötigt Rüdiger Schmidt - Februar 2006 - TU Darmstadt 12

Energy loss for charged particles by synchrotron radiation Radius Lorenz Force = accelerating force charged particle Particle trajectory Figure from K. Wille Radiation field Rüdiger Schmidt - Februar 2006 - 13

Energy loss for charged particles electrons / protons in LEP tunnel Rüdiger Schmidt - Februar 2006 - TU Darmstadt 14

. . . just assuming to accelerate electrons to 7 Te. V . . . better to accelerate protons Rüdiger Schmidt - Februar 2006 - TU Darmstadt 15

LHC Layout Beam dump blocks IR 5: CMS eight arcs (sectors) eight long straight section (about 700 m long) IR 4: RF + Beam instrumentation IR 3: Momentum Cleaning (warm) IR 6: Beam dumping system IR 7: Betatron Cleaning (warm) IR 8: LHC-B IR 2: ALICE IR 1: ATLAS Injection Rüdiger Schmidt - Februar 2006 - TU Darmstadt Injection 16

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 10 -6 rad, two particles would separate by 1 m after 106 m. At the LHC, with a length of 26860 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 - Februar 2006 - TU Darmstadt 17

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, 106 turns) Rüdiger Schmidt - Februar 2006 - TU Darmstadt 18

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 1034 [cm-1 s-2] • LEP (e+e-) : • Tevatron (p-pbar) : • B-Factories: 3 -4 1031 [cm-1 s-2] 3 1031 [cm-1 s-2] 1034 [cm-1 s-2] Rüdiger Schmidt - Februar 2006 - TU Darmstadt 19

Luminosity parameters Rüdiger Schmidt - Februar 2006 - TU Darmstadt 20

Beam beam interaction determines parameters Number of protons N per bunch limited to about 1011 f = 11246 Hz Beam size σ = 16 m for = 0. 5 m with one bunch Nb=1 with Nb = 2808 bunches (every 25 ns one bunch) L = 1034 [cm-2 s-1] Rüdiger Schmidt - Februar 2006 - TU Darmstadt 21

Large number of bunches IP l Crossing angle to avoid parasitic beam interaction Rüdiger Schmidt - Februar 2006 - TU Darmstadt 22

Large number of bunches IP l Crossing angle to avoid parasitic beam interaction Rüdiger Schmidt - Februar 2006 - TU Darmstadt 23

Crossing angle for multibunch operation u u u Total crossing angle of 300 rad Beam size at IP 16 m, in arcs about 1 m Beams in the arcs in two vacuum chambers Rüdiger Schmidt - Februar 2006 - TU Darmstadt 24

summarising constraints and consequences…. Centre-of-mass energy must well exceed 1 Te. V, 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 1034 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 - Februar 2006 - TU Darmstadt 25

Very high beam current Many bunches and high energy Energy stored in one beam about 362 MJ l l l Dumping the beam in a safe way Beam induced quenches (when 10 -7 of beam hits magnet at 7 Te. V) Beam cleaning (Betatron and momentum cleaning) Rüdiger Schmidt - Februar 2006 - TU Darmstadt 26

Livingston type plot: Energy stored in the beam courtesy R. Assmann Transverse energy even Rüdiger Schmidt - Februar 2006 density: - TU Darmstadt a factor of 1000 larger 27

LHC accelerator in the tunnel LHC Main Systems Superconducting magnets Cryogenics Vacuum system Powering (industrial use of High Temperature Superconducting material) Rüdiger Schmidt - Februar 2006 - TU Darmstadt 28

Regular arc: Magnets 1232 main dipoles + 392 main quadrupoles + 2500 corrector magnets Rüdiger Schmidt - Februar 2006 - TU Darmstadt 3700 multipole corrector magnets 29

Regular arc: Connection via service module and jumper Supply and recovery of helium with 26 km long cryogenic distribution line Cryogenics Static bath of superfluid helium at 1. 9 K in cooling loops of 110 m length Rüdiger Schmidt - Februar 2006 - TU Darmstadt 30

Regular arc: Beam vacuum for Vacuum Beam 1 + Beam 2 Insulation vacuum for the cryogenic distribution line Insulation vacuum for the magnet cryostats Rüdiger Schmidt - Februar 2006 - TU Darmstadt 31

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) Rüdiger Schmidt - Februar 2006 - TU Darmstadt 32

Dipole magnets for the LHC 1232 Dipolmagnets Length about 15 m Magnetic Field 8. 3 T Two beam tubes with an opening of 56 mm Rüdiger Schmidt - Februar 2006 - TU Darmstadt 33

Coils for Dipolmagnets 15 m long Rüdiger Schmidt - Februar 2006 - TU Darmstadt 34

Superconducting cable for 12 k. A 15 mm / 2 mm Temperature 1. 9 K cooled with Helium Force on the cable: F = B * I 0 * L with B = 8. 33 T I 0 = 12000 Ampere 56 mm L = 15 m F = 165 tons Rüdiger Schmidt - Februar 2006 - TU Darmstadt 35

Ferromagnetic iron Nonmagetic collars Supraconducting coil Beam tubes Steelcylinder for Helium Insulationvacuum Vacuumtank Supports Rüdiger Schmidt - Februar 2006 - TU Darmstadt 36

First cryodipole lowered on 7 March 2005 Only one access point for 15 m long dipoles, 35 tons. Rüdiger each. Schmidt - Februar 2006 - TU Darmstadt 37

Transport in the tunnel with an optical guided vehicle about 1600 magnets to be transported for 15 km at 3 km/hour Rüdiger Schmidt - Februar 2006 - TU Darmstadt 38

Operation and machine protection Rüdiger Schmidt - Februar 2006 - TU Darmstadt 39

LHC magnetic cycle energy ramp coast 7 Te. V start of the ramp injection phase preparation and access 450 Ge. V L. Bottura Rüdiger Schmidt - Februar 2006 - TU Darmstadt 40

LHC magnetic cycle - Beam injection beam dump 7 Te. V injection phase 12 batches from the SPS (every 20 sec) one batch 216 / 288 bunches 450 Ge. V L. Bottura Rüdiger Schmidt - Februar 2006 - TU Darmstadt 41

SPS experiment: Beam damage at 450 Ge. V Controlled SPS experiment l l 8 1012 protons clear damage beam size σx/y = 1. 1 mm/0. 6 mm above damage limit l 2 1012 protons below damage limit 25 cm 6 cm V. Kain et al 0. 1 % of the full LHC beams Rüdiger Schmidt - Februar 2006 - TU Darmstadt 42

Regular (very healthy) operation Assuming that the beams are colliding at 7 Te. V Single beam lifetime larger than 100 hours…. . Collision of beams with a luminosity of 1034 cm-2 s-1 • lifetime of the beam can be be dominated by collisions • 109 protons / second lost per beam / per experiment (in IR 1 and IR 5 - high luminosity insertions) Rüdiger Schmidt - Februar 2006 - TU Darmstadt 43

End of data taking in normal operation l l l Luminosity lifetime estimated to be approximately 10 h (after 10 hours only 1/3 of initial luminosity) Beam current somewhat reduced - but not much Energy per beam still about 200 -300 MJ Beams are extracted in beam dump blocks The only component that can stand a fast loss of the full beam at top energy is the beam dump block - all other components would be damaged At 7 Te. V, fast beam losses with an intensity of about 5% of a “nominal bunch” could damage superconducting coils Rüdiger Schmidt - Februar 2006 - TU Darmstadt 44

Beam lifetime with nominal intensity at 7 Te. V Beam lifetime Beam power into equipment (1 beam) Comments 100 h 1 k. W Healthy operation 10 h 10 k. W Operation acceptable, collimation must absorb large fraction of beam energy (approximately beam losses = cryogenic cooling power at 1. 9 K) 0. 2 h 500 k. W Operation only possibly for short time, collimators must be very efficient 1 min 6 MW Equipment or operation failure operation not possible - beam must be dumped << 1 min > 6 MW Beam must be dumped VERY FAST Failures will be a part of the regular operation and MUST be anticipated Rüdiger Schmidt - Februar 2006 - TU Darmstadt 45

Beam losses into material l l Proton losses lead to particle cascades in materials The energy deposition leads to a temperature increase For the maximum energy deposition as a function of material there is no straightforward expression 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 Rüdiger Schmidt - Februar 2006 - TU Darmstadt 46

Full LHC beam deflected into copper target 2808 bunches Copper target 2 m Energy density [Ge. V/cm 3] on target axis vaporisation melting Target length [cm] N. Tahir (GSI) et al. Rüdiger Schmidt - Februar 2006 - TU Darmstadt 47

Density change in target after impact of 100 bunches copper solid state radial 100 bunches – target density reduced to 10% Target radial coordinate [cm] • • Energy deposition calculations using FLUKA Numerical simulations of the hydrodynamic and thermodynamic response of the target with twodimensional hydrodynamic computer code Rüdiger Schmidt - Februar 2006 - TU Darmstadt N. Tahir (GSI) et al. 48

Operational margin of a superconducting magnet Applied Magnetic Field [T] Bc critical field Bc quench with fast loss of ~5 · 106 protons 8. 3 T QUENCH quench with fast loss of ~5 · 109 protons 0. 54 T 1. 9 K Rüdiger Schmidt - Februar 2006 - TU Darmstadt Tc critical Tc temperature 9 K 49

Quench - transition from superconducting state to normalconducting state Quenches are initiated by an energy in the order of m. J (corresponds to the energy of 1000 protons at 7 Te. V) 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 1 s 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 Rüdiger Schmidt - Februar 2006 - TU Darmstadt 50

Schematic layout of beam dump system in IR 6 Septum magnet deflecting the extracted beam Beam 1 Q 5 L H-V kicker for painting the beam Beam Dump Block Q 4 L about 700 m Fast kicker magnet Q 4 R about 500 m Q 5 R Beam 2 Rüdiger Schmidt - Februar 2006 - TU Darmstadt 51

Beam Dump Block - Layout beam absorber (graphite) about 8 m concrete shielding L. Bruno Rüdiger Schmidt - Februar 2006 - TU Darmstadt 52

Beam on Beam Dump Block 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 about 35 cm beam impact within less than 0. 1 ms M. Gyr Rüdiger Schmidt - Februar 2006 - TU Darmstadt 53

Temperature of beam dump block at 80 cm inside up to 800 0 C L. Bruno: Thermo-Mechanical Analysis with ANSYS Rüdiger Schmidt - Februar 2006 - TU Darmstadt 54

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 Te. V with fully squeezed beams), particles will always touch collimators first ! Rüdiger Schmidt - Februar 2006 - TU Darmstadt 55

56. 0 mm +- 3 ~1. 3 mm Beam +/- 3 sigma Beam in vacuum chamber with beam screen at 7 Te. V Rüdiger Schmidt - Februar 2006 - TU Darmstadt 56

56. 0 mm Collimators at 7 Te. V, squeezed optics 1 mm R. Assmanns EURO +/- 8 sigma = 4. 0 mm Beam +/- 3 sigma Example: Setting of collimators at 7 Te. V - with luminosity optics Beam must always touch collimators first ! Rüdiger Schmidt - Februar 2006 - TU Darmstadt 57

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 - Februar 2006 - TU Darmstadt 58

RF contacts for guiding image currents 2 mm Beam spot Rüdiger Schmidt - Februar 2006 - TU Darmstadt 59

Conclusions Rüdiger Schmidt - Februar 2006 - TU Darmstadt 60

Recalling LHC challenges l l l Enormous amount of equipment Complexity of the LHC accelerator New challenges in accelerator physics with LHC beam parameters pushed to the extreme Fabrication of equipment Installation LHC “hardware” commissioning LHC Beam commissioning 1 2 3 4 5 6 7 8 9 10 11 12 2004 1 2 3 4 5 6 7 8 9 10 11 12 2005 1 2 3 4 5 6 7 8 9 10 11 12 2006 Rüdiger Schmidt - Februar 2006 - TU Darmstadt 1 2 3 4 5 6 7 8 9 10 11 12 2007 61

Conclusions l The LHC is a global project with the world-wide highenergy 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 l No one has ny doubt that it will be a great challenge for both machine to reach design luminosity and for the detectors to swallow it. 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 - Februar 2006 - TU Darmstadt 62

Acknowledgement The LHC accelerator is being realised by CERN supported by the member states, in collaboration with institutes from many countries over a period of more than 20 years Many contribution come from the USA, 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, L. Bottura, L. Bruno, R. Denz, A. Ferrari, B. Goddard, M. Gyr, D. Hagedorn, J. B. Jeanneret, P. Proudlock, B. Puccio, F. Rodriguez-Mateos, F. Ruggiero, L. Rossi, S. Russenschuck, P. Sievers, G. Stevenson, A. Verweij, V. Vlachoudis, L. Vos Rüdiger Schmidt - Februar 2006 - TU Darmstadt 63

Some references Accelerator physics l Proceedings of CERN ACCELERATOR SCHOOL (CAS), http: //schools. web. cern. ch/Schools/CAS_Proceedings. html • In particular: 5 th 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 2003 -002 -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 2003 Rüdiger Schmidt - Februar 2006 - TU Darmstadt 64

The CERN accelerator complex: injectors and transfer 5 LHC 4 Beam 1 Beam 2 6 7 3 2 SPS TI 8 TI 2 protons LINACS Autumn 2004 1 Booster CPS Ions LEIR 8 High intensity beam from the SPS into LHC at 450 Ge. V via TI 2 and TI 8 LHC accelerates to 7 Te. V Beam size of protons decreases with energy: 2 = 1 / E Beam size large at injection Beam fills vacuum chamber at 450 Ge. V Rüdiger Schmidt - Februar 2006 - TU Darmstadt 65

Energy stored in one beam at 7 Te. V: 362 MJoule Kugelstossen: shot The energy of one shot (5 kg) at 800 km/hour corresponds to the energy stored in one bunch at 7 Te. V. There are 2808 bunches. Factor 200 compared to HERA, TEVATRON and SPS. Rüdiger Schmidt - Februar 2006 - TU Darmstadt 66

Magnetic field - current density - temperature Superconducting material determines: Tc critical temperature Bc critical field Bc Production process: Jc critical current density Tc Lower temperature increased current density Typical for Nb. Ti: 2000 A/mm 2 @ 4. 2 K, 6 T Copyright A. Verweij Für 10 T, Operation less than 1. 9 K required Rüdiger Schmidt - Februar 2006 - TU Darmstadt 67