R.Schmidt - TU Darmstadt Januar 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

R.Schmidt - TU Darmstadt Januar Vortrag GradKolleg 2004

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

R.Schmidt - TU Darmstadt Januar 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 -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.... )

R.Schmidt - TU Darmstadt Januar The CERN Beschleuniger Komplex LEP e+e- ( ) 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

R.Schmidt - TU Darmstadt Januar 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 - TU Darmstadt Januar 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 magnets powered in 1712 electrical circuits

R.Schmidt - TU Darmstadt Januar 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

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

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

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

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

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

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

R.Schmidt - TU Darmstadt Januar 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

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

R.Schmidt - TU Darmstadt Januar 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 -2 s -1 ] Tevatron (p-pbar) : some [cm -2 s -1 ] B-Factories : >10 34 [cm -2 s -1 ] ~40 m in straight section (not to scale) IP

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

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

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

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

R.Schmidt - TU Darmstadt Januar 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 !!

R.Schmidt - TU Darmstadt Januar Very high beam current: consequences 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) 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

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

R.Schmidt - TU Darmstadt Januar 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

R.Schmidt - TU Darmstadt Januar 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 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

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

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

R.Schmidt - TU Darmstadt Januar main dipoles multipole corrector magnets 392 main quadrupoles corrector magnets Regular arc: Magnets

R.Schmidt - TU Darmstadt Januar 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

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

R.Schmidt - TU Darmstadt Januar 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]

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

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

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

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

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

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

R.Schmidt - TU Darmstadt Januar Operation and machine protection

R.Schmidt - TU Darmstadt Januar 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

R.Schmidt - TU Darmstadt Januar 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 - TU Darmstadt Januar 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

R.Schmidt - TU Darmstadt Januar 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

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

R.Schmidt - TU Darmstadt Januar 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

R.Schmidt - TU Darmstadt Januar 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 beam area 6 cm 8     10 12

R.Schmidt - TU Darmstadt Januar 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

R.Schmidt - TU Darmstadt Januar 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.

R.Schmidt - TU Darmstadt Januar 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.

R.Schmidt - TU Darmstadt Januar 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

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

R.Schmidt - TU Darmstadt Januar 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 - TU Darmstadt Januar 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

R.Schmidt - TU Darmstadt Januar 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

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

R.Schmidt - TU Darmstadt Januar 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 - TU Darmstadt Januar  ~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

R.Schmidt - TU Darmstadt Januar 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

R.Schmidt - TU Darmstadt Januar 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

R.Schmidt - TU Darmstadt Januar LHC Sector 78 – First cooldown  From 300K to 80K precooling with LN 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 tons of material to be cooled.  From 4.5K to 1.9K. Cold compressors at 15 mbar. Four days for the first sector.

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

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

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

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

R.Schmidt - TU Darmstadt Januar Conclusions

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

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

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

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

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

R.Schmidt - TU Darmstadt Januar 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

R.Schmidt - TU Darmstadt Januar 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 - TU Darmstadt Januar 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

R.Schmidt - TU Darmstadt Januar Acknowledgement 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

R.Schmidt - TU Darmstadt Januar 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……..