1. R.Schmidt - TU Darmstadt Januar 20081 Der LHC Beschleuniger am CERN: Kollisionen intensiver Teilchenstrahlen bei hoher Strahlenergie Der LHC Beschleuniger am CERN: Kollisionen intensiver Teilchenstrahlen bei hoher Strahlenergie Rüdiger Schmidt - CERN TU Darmstadt Januar 2008 Der LHC: “Just another collider?” Kollision intensiver Teilchenstrahlen Injectorkomplex und LHC Operation und Betriebssicherheit Status und Ausblick

2. R.Schmidt - TU Darmstadt Januar 20082 Vortrag GradKolleg 2004

3. R.Schmidt - TU Darmstadt Januar 2008 3 Installation of cryogenic distribution line in the LHC tunnel – started during summer 2003 Status 2007

4. R.Schmidt - TU Darmstadt Januar 2008 4 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 10 34 [cm -2 s -1 ] (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.... )

5. R.Schmidt - TU Darmstadt Januar 2008 5 The CERN Beschleuniger Komplex LEP e+e- (1989-2000) 104 GeV/c LHC pp und Ionen 7 TeV/c 26.8 km Umfang 8.3 Tesla supraleitende Magnete CERN Hauptgelände Schweiz Genfer See Frankreich LHC Beschleuniger (etwa 100m unter der Erde) SPS Beschleuniger CERN- Prevessin CMS ALICELHCbATLAS

6. R.Schmidt - TU Darmstadt Januar 2008 6 The LHC: just another collider ? NameStartParticlesMax proton energy [GeV] Length [m] B Field [Tesla] Stored beam energy [MJoule] TEVATRON Fermilab Illinois USA 1983p-pbar98063004.51.6 for protons HERA DESY Hamburg Germany 1992p – e+ p – e- 92063005.52.7 for protons RHIC Brookhaven Long Island USA 2000Ion-Ion p-p 25038344.30.9 per proton beam LHC CERN Geneva Switzerland 2008Ion-Ion p-p 7000268008.3362 per proton beam

7. R.Schmidt - TU Darmstadt Januar 2008 7 Challenges for LHC l High-field (8.3 Tesla) superconducting magnets operating at a temperature of 1.9 K with an energy stored in the magnets of 10 GJ l Beam-parameters pushed to the extreme Energy stored in the beam two orders of magnitude above others Transverse energy density three orders of magnitude compared to other accelerators Consequences for several systems (machine protection, collimation, vacuum system, cryogenics, …) l GJoule beams running through superconducting magnets that quench with mJoule l Complexity of the accelerator (most complex scientific instrument ever constructed) with 10000 magnets powered in 1712 electrical circuits

8. R.Schmidt - TU Darmstadt Januar 2008 8 New approaches and novel technologies l Two-In-One superconducing magnets inside helium 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 convertors and control of the current with an unprecedented accuracy of 1 ppm l New devices and materials for absorbing the particles l Radiation studies for the accelerator at an unprecedented scale l Development of radiation tolerant electronics and highly radiation resistant optical fibres l Overall consideration for machine protection: an accidental release of the energy can lead to massive damage l Approach for machine protection systems driven by studies on safety, reliability and availability using formal methods

9. R.Schmidt - TU Darmstadt Januar 2008 9 A total number of 1232 dipole magnets are required to close the circle

10. R.Schmidt - TU Darmstadt Januar 2008 10 LHC dipole magnet lowered into the tunnel First cryodipole lowered on 7 March 2005 Descent of the last magnet, 26 April 2007

11. R.Schmidt - TU Darmstadt Januar 2008 11 Interconnecting two magnets out of 1700

12. R.Schmidt - TU Darmstadt Januar 2008 12 Current leads with High Temperature Superconductor 12 Feedboxes (‘DFB’) : transition from copper cable to super-conductor Water cooled Cu cables

13. R.Schmidt - TU Darmstadt Januar 2008 13 DFB with ~17 out of 1600 HTS current leads

14. R.Schmidt - TU Darmstadt Januar 2008 14 RF cavities, four per beam with some 10 MVolt

15. R.Schmidt - TU Darmstadt Januar 2008 15 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 2008 : Commissioning with beam planned

16. R.Schmidt - TU Darmstadt Januar 2008 16 Colliding very intense proton beams

17. R.Schmidt - TU Darmstadt Januar 2008 17 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 10 34 [cm -1 s -2 ] LEP (e+e-) : 3-4 10 31 [cm -2 s -1 ] Tevatron (p-pbar) : some 10 32 [cm -2 s -1 ] B-Factories : >10 34 [cm -2 s -1 ] ~40 m in straight section (not to scale) IP

18. R.Schmidt - TU Darmstadt Januar 2008 18 Luminosity parameters What happens with one particle experiencing the force of the em-fields or 10 11 protons in the other beam during the collision ?

19. R.Schmidt - TU Darmstadt Januar 2008 19 Limitation: beam-beam interaction

20. R.Schmidt - TU Darmstadt Januar 2008 20 Electromagnetic force on a particle in the counterrotating beam Bunch intensity limited due to this strong non- linearity to about N = 10 11 Optimising luminosity by increasing N

21. R.Schmidt - TU Darmstadt Januar 2008 21 Beam beam interaction determines parameters Number of protons N per bunch limited to about 10 11 f = 11246 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 = 10 34 [cm -2 s -1 ] => 362 MJoule per beam

22. R.Schmidt - TU Darmstadt Januar 2008 22 Livingston type plot: Energy stored magnets and beam based on graph from R.Assmann

23. R.Schmidt - TU Darmstadt Januar 2008 23 What does this mean? 10 GJoule: the energy of an A380 at 700 km/hour corresponds to the energy stored in the LHC magnet system: Sufficient to heat up and melt 12 tons of Copper!! 362 MJoule: the energy stored in one LHC beam corresponds approximately to… 90 kg of TNT 8 litres of gasoline 15 kg of chocolate It’s how ease the energy is released that matters most !!

24. R.Schmidt - TU Darmstadt Januar 2008 24 Very high beam current: consequences l Dumping the beam in a safe way l Beam induced quenches (when 10 -8 -10 -7 of beam hits magnet at 7 TeV) l Beam cleaning (Betatron and momentum cleaning) l Radiation, in particular in experimental areas from beam collisions (beam lifetime is dominated by this effect) l Beam instabilities due to impedance l Synchrotron radiation at 7 TeV - power to cryogenic system l Photo electrons - accelerated by the following bunches l Single particle dynamics: dynamic aperture and magnet field quality, in particular in the presence of dynamic effects in superconducing magnets during the ramp

25. R.Schmidt - TU Darmstadt Januar 2008 25 The LHC accelerator complex Complexity due to the LHC main ring AND due to the injector chain

26. R.Schmidt - TU Darmstadt Januar 2008 26 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 Beam Cleaning (warm) IR7: Betatron Beam Cleaning (warm) Beam dump blocks

27. R.Schmidt - TU Darmstadt Januar 2008 27 The CERN accelerator complex: injectors and transfer High intensity beam from the SPS into LHC at 450 GeV via TI2 and TI8 LHC accelerates from 450 GeV to 7 TeV LEIR CPS SPS Booster LINACS LHC 3 4 5 6 7 8 1 2 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

28. R.Schmidt - TU Darmstadt Januar 2008 28 TI 8 LHC SPS 6911 m 450 GeV LSS6 IR2 TT40 LSS4 IR8 TI 8 beam tests 23/24.10.04 6/7.11.04 TI 2 beam test 28/29.10.07 combined length 5.6 km over 700 magnets ca. 2/3 of SPS LHC transfer lines and injections - overview TT40 beam tests 8.9.03 TI 2

29. R.Schmidt - TU Darmstadt Januar 2008 29 Transfer line TI8 (MIBT magnet)

30. R.Schmidt - TU Darmstadt Januar 2008 30 LHC accelerator LHC Main Systems Superconducting magnets Cryogenics Vacuum system Powering (industrial use of High Temperature Superconducting material)

31. R.Schmidt - TU Darmstadt Januar 2008 31 1232 main dipoles + 3700 multipole corrector magnets 392 main quadrupoles + 2500 corrector magnets Regular arc: Magnets

32. R.Schmidt - TU Darmstadt Januar 2008 32 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

33. R.Schmidt - TU Darmstadt Januar 2008 33 1232 Dipolemagnets Length about 15 m Magnetic Field 8.3 T Two beam tubes with an opening of 56 mm Dipole magnets for the LHC

34. R.Schmidt - TU Darmstadt Januar 2008 34 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 T [K] B [T] J [kA/mm 2 ] Operating temperature of superconductors J [kA/mm2]

35. R.Schmidt - TU Darmstadt Januar 2008 35 Critical current density of technical superconductors + 3 tesla Ph.Lebrun

36. R.Schmidt - TU Darmstadt Januar 2008 36 Beam tubes Supraconducting coil Nonmagetic collars Ferromagnetic iron Steelcylinder for Helium Insulationvacuum Supports Vacuumtank Dipole magnet cross section 16 mBar cooling tube

37. R.Schmidt - TU Darmstadt Januar 2008 37 Specific heat of liquid helium and copper Discovery of He II phase transition (1927) by W.H. Keesom and M.Wolfke

38. R.Schmidt - TU Darmstadt Januar 2008 38 Equivalent thermal conductivity of He II Copper OFHC Helium II G. Bon Mardion et al.

39. R.Schmidt - TU Darmstadt Januar 2008 39 Principle of He II cooling of LHC magnets

40. R.Schmidt - TU Darmstadt Januar 2008 40 4 stages 1st stage cartridge Air Liquide & IHI-Linde Axial-centrifugal impeller Cold compressors of LHC 1.8 K units

41. R.Schmidt - TU Darmstadt Januar 2008 41 Operation and machine protection

42. R.Schmidt - TU Darmstadt Januar 2008 42 injection phase 12 batches from the SPS (every 20 sec) one batch 216 / 288 bunches LHC magnetic cycle and beam operation L.Bottura 450 GeV 7 TeV beam dump energy ramp coast coast (2  360 MJ) start of the ramp

43. R.Schmidt - TU Darmstadt Januar 2008 43 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

44. R.Schmidt - TU Darmstadt Januar 2008 44 What happens in case the full LHC beam impact onto material? Since 2003/4 collaboration with GSI and TU Darmstadt, N.Tahir (GSI), D.H.H.Hoffmann and many others

45. R.Schmidt - TU Darmstadt Januar 2008 45 Beam losses into material l Proton losses into material lead to particle cascades l The energy deposition increases the temperature 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 The material could be damaged….. losing their performance (mechanical strength) melting and vaporisation Magnets could quench….. beam lost - re-establish condition will take hours Repair could take a long time

46. R.Schmidt - TU Darmstadt Januar 2008 46 Damage of material for impact of a pencil beam copper graphite

47. R.Schmidt - TU Darmstadt Januar 2008 47 Full LHC beam deflected into copper target Target length [cm] vaporisation melting Copper target 2 m Energy density [GeV/cm 3 ] on target axis 2808 bunches

48. R.Schmidt - TU Darmstadt Januar 2008 48 SPS experiment: Beam damage at 450 GeV Controlled SPS experiment l 8  10 12 protons clear damage l beam size σ x/y = 1.1mm/0.6mm above damage limit l 2  10 12 protons below damage limit 25 cm 0.1 % of the full LHC beam energy 10 times the beam area 6 cm 8  10 12 6  10 12 4  10 12 2  10 12

49. R.Schmidt - TU Darmstadt Januar 2008 49 STEP1: Calculation of energy deposition of a 7 TeV proton beam in material with a beam of  =0.2 mm (FLUKA) copper, one bunch carbon, one bunch copper, per proton carbon, one bunch at 16 cm

50. R.Schmidt - TU Darmstadt Januar 2008 50 STEP2: Hydrodynamic simulations with BIG-2 including the response of the target with LHC beam for copper After an impact of some bunches, pressure and temperature in the beam heated region increase drastically. A hydrodynamic simulation with a model including a multiphase semi-empirical equation-of-state describes the target behaviour during the diffferent phases of heating and expansion. State changes and pressure waves are taken into account by the numerical simulation. N.Tahir (GSI), D.H.H.Hoffmann et al.

51. R.Schmidt - TU Darmstadt Januar 2008 51 Target radial coordinate [cm] radial copper solid state 100 bunches – target density reduced to ~10% Density change at 16 cm in target after impact of 100 bunches N.Tahir (GSI), D.H.H.Hoffmann et al. After an impact of about 100 bunches, the beam heated region has expanded drastically and the density in the inner region decreases by about a factor of ~10. The bulk of the following beam will not be absorbed and continues to tunnel further and further into the target, between 20 and 40 m. Such effects have been observed for heavy ion beams. The LHC might be an interesting tool to study HighEnergyDensityMatter.

52. R.Schmidt - TU Darmstadt Januar 2008 52 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

53. R.Schmidt - TU Darmstadt Januar 2008 53 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

54. R.Schmidt - TU Darmstadt Januar 2008 54 L.Bruno: Thermo-Mechanical Analysis with ANSYS Temperature of beam dump block at 80 cm inside up to 800 0 C

55. R.Schmidt - TU Darmstadt Januar 2008 55 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]

56. R.Schmidt - TU Darmstadt Januar 2008 56 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 Multi-stage beam halo cleaning (collimation) system to protect sensitive LHC magnets from beam induced quenches and damage Halo particles are first scattered by the primary collimator (closest to beam) Scattered particles (forming the secondary halo) are absorbed by the secondary collimators, or scattered to form the tertiary halo. More than 100 collimators jaws needed for the nominal LHC beam. Primary and secondary 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

57. R.Schmidt - TU Darmstadt Januar 2008 57 Accidental kick by the beam dump kicker at 7 TeV part of beam touches collimators (about 20 bunches from 2808) P.Sievers / A.Ferrari / V. Vlachoudis Beryllium

58. R.Schmidt - TU Darmstadt Januar 2008 58 RF contacts for guiding image currents Beam spot

59. R.Schmidt - TU Darmstadt Januar 2008 59 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!

60. R.Schmidt - TU Darmstadt Januar 2008 60 +- 3  ~1.3 mm 56.0 mm Beam in vacuum chamber with beam screen at 7 TeV Interception of beam- induced heat loads at 5-20 K (supercritical helium) Shielding of the 1.9 K cryopumping surface from synchrotron radiation High-conductivity copper lining for low beam impedance Low-reflectivity sawtooth surface at equator to reduce photoemission and electron cloud

61. R.Schmidt - TU Darmstadt Januar 2008 61 About 3600 beam loss monitors to detect particle losses and to trigger a beam dump Ionization chambers to detect beam losses –Montitors in the arc –Monitors close to all collimators –Simulation and experiments to determine threshold for beam losses Student from TU Darmstadt involved for his Masters project

62. R.Schmidt - TU Darmstadt Januar 2008 62 Status summary l Installation and magnet interconnections finished l Cryogenics Nearly finished and operational (e.g. cryoplants) Two sectors been at 1.9 K, third sector being cooled down Cooldown for other sectors to start soon l Powering system: commissioning on the way Power converters commissioning on short circuits in tunnel finished Magnet powering tests started in two sectors, main dipoles at 8.5 kA corresponding to 5 TeV l Other systems (RF, Beam injection and extraction, Beam instrumentation, Collimation, Interlocks, Controls) Essentially on schedule for first beam in 2008 l Injector complex and transfer lines ready

63. R.Schmidt - TU Darmstadt Januar 2008 63 LHC Sector 78 – First cooldown  From 300K to 80K precooling with LN2. 1200 tons of LN2 (64 trucks of 20 tons). Three weeks for first sector.  From 80K to 4.5K. Cooldown with refrigerator. Three weeks for the first sector. 4700 tons of material to be cooled.  From 4.5K to 1.9K. Cold compressors at 15 mbar. Four days for the first sector.

64. R.Schmidt - TU Darmstadt Januar 2008 64 Magnet temperature in one sector

65. R.Schmidt - TU Darmstadt Januar 2008 65 Courtesy F.Bordry 2ppm Current tracking between the three main circuits of Sector 78

66. R.Schmidt - TU Darmstadt Januar 2008 66 Ramping the dipole magnets to a current for 5 TeV 8000 A 4000 A Dipole magnet current 12 hours

67. R.Schmidt - TU Darmstadt Januar 2008 67 Temperature after an induced quench 10 minutes

68. R.Schmidt - TU Darmstadt Januar 2008 68 Conclusions

69. R.Schmidt - TU Darmstadt Januar 2008 69 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

70. R.Schmidt - TU Darmstadt Januar 2008 70 Typical (recent) examples

71. R.Schmidt - TU Darmstadt Januar 2008 71 Repair of the inner triplett

72. R.Schmidt - TU Darmstadt Januar 2008 72 RF bellows in the 1700 interconnections

73. R.Schmidt - TU Darmstadt Januar 2008 73 Arc plug-in module at warm temperature

74. R.Schmidt - TU Darmstadt Januar 2008 74 Arc plug-in module at working temperature

75. R.Schmidt - TU Darmstadt Januar 2008 75 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

76. R.Schmidt - TU Darmstadt Januar 2008 76 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 200520062007 1 2 3 4 5 6 7 8 9 10 11 12 Fabrication of equipment Installation LHC Beam commissioning LHC “hardware” commissioning 2008 1 2 3 4 5 6 7 8 9 10 11 12

77. R.Schmidt - TU Darmstadt Januar 2008 77 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 We recognize that the planned schedule is very aggressive, given the complexity and potential for damage involved in the initial phases of operation. l It will be important to understand the performance of the machine protection system, the collimation system and the orbit feedback system as well as cycle repeatability and adequate beta-beat control before proceeding to run with significant stored beam energy. Pressure to take shortcuts must be resisted. Machine Advisory Committee, chaired by Prof. M. Tigner, June 2005

78. R.Schmidt - TU Darmstadt Januar 2008 78Acknowledgement 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 the USA, Russia, India, Canada, special contributions from France and Switzerland Industry plays a major role in the construction of the LHC TU Darmstadt and GSI among the contributors Thanks for the material from: R.Assmann, R.Bailey, F.Bordry, L.Bottura, L.Bruno, L.Evans, B.Goddard, M.Gyr, Ph.Lebrun

79. R.Schmidt - TU Darmstadt Januar 2008 79 Vielen Dank für die Einladung l Möglichkeiten für zukünftige Zusammenarbeit im Bereich von Strahlverlust, Betriebssicherheit, HighEnergyDensity States of Matter,….. l Beteiligung bei einem SPS Experiment, in dem der hochintensive 450 GeV Strahl auf Targets gelenkt wird? l Viele andere Bereiche……..