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Status of the LHC

This paper discusses the current status of the Large Hadron Collider (LHC) and its challenges, including the energy achieved, the dipole field, the luminosity, and the operating difficulties. It also covers the installation, preparation for beam, incidents, repairs, and beam operations at the LHC.

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Status of the LHC

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  1. Status of the LHC J. Wenninger CERN Beams Department Operation Group Status of the LHC - Rencontres de Moriond Rencontres de Moriond EW 2010 6-13 March 2010

  2. Outline Introduction Installation and preparation for beam Incident in sector 34 and repair LHC beam operation Conclusions Status of the LHC - Rencontres de Moriond

  3. LHC rings in the LEP tunnel CMS ATLAS 26.7 km LEP/LHC tunnel Depth 70-140 m Status of the LHC - Rencontres de Moriond LHCB CERN Central Control room ALICE

  4. ATLAS Status of the LHC - Rencontres de Moriond

  5. CMS Status of the LHC - Rencontres de Moriond

  6. LHCb Status of the LHC - Rencontres de Moriond

  7. ALICE Status of the LHC - Rencontres de Moriond

  8. TOTEM and LHCf Total X-section, elastic and diffractive scattering Forward production of neutral particles (cosmic ray shower modeling) Status of the LHC - Rencontres de Moriond

  9. LHC challenges • The LHC surpasses existing accelerators/colliders in 2 aspects: • The energy of the beam of 7 TeV that is achieved within the size constraints of the existing 26.7 km LEP tunnel. • LHC dipole field 8.3 T • HERA/Tevatron ~ 4 T • The luminosity of the collider: • LHC pp ~ 1034 cm-2 s-1 • Tevatron pp 3x1032 cm-2 s-1 • SppS pp 6x1030 cm-2 s-1 • Very high field magnets and very high beam intensities: • Operating the LHC is a great challenge. • There is a significant risk to the equipment and experiments. A factor 2 in field A factor 4 in size Status of the LHC - Rencontres de Moriond A factor 30 in luminosity

  10. LHC dipole magnet • 1232 dipolemagnets. • B field 8.3 T (11.8 kA) @ 1.9 K (superfluidHelium) • 2 magnets-in-one design: two beam tubes with an opening of 56 mm. • Operating challenges: • Dynamicfield changes at injection. • Verylowquenchlevels (~ mJ/cm3) Status of the LHC - Rencontres de Moriond

  11. Stored energy • Increase with respect to existing accelerators : • A factor 2 in magnetic field • A factor 7 in beam energy • A factor 200 in stored beam energy Status of the LHC - Rencontres de Moriond Damage threshold

  12. Setting the scale • The 11 GJ of enery stored in the magnets are sufficient to heat and melt 15 tons of Copper (~1.7 m3). • The 350 MJ stored in each beam correspond to ~90 kg of TNT. • Plasma-hydrodynamic simulations indicate that the beam will drill a ~30 m long hole into Copper. Status of the LHC - Rencontres de Moriond As an indication… Few cm long groove on an SPS vacuum chamber from the impact of ~1% of a nominal LHC beam during a beam incident

  13. Collimation 1.2 m beam To operate at nominal performance the LHC requires a large and complex collimation system • Ensure ‘cohabitation’ of: • 360 MJ of stored beam energy, • super-conducting magnets with quench limits of few mJ/cm3 • Almost 100 collimators and absorbers. • Organized in 4 stages / levels. • Alignment tolerances < 0.1 mm to ensure that over 99.99% of the protons are intercepted. • Primary and secondary collimators are made of Carbon to survive large beam loss. Status of the LHC - Rencontres de Moriond

  14. Outline Introduction Installation and preparation for beam Incident in sector 34 and repair LHC beam operation Conclusions Status of the LHC - Rencontres de Moriond

  15. Installation First dipole lowered March 2005 Status of the LHC - Rencontres de Moriond • Transport in the tunnel with an optically guided vehicle. • Approximately 1600 magnet assemblies transported over up to 20 km at 3 km/hour.

  16. 3 km long arc cryostat Status of the LHC - Rencontres de Moriond

  17. LHC cool-down 2008 First beam around the LHC All sectors at nominal temperature Cool-down time to 1.9 K is nowadays ~4 weeks/sector [sector = 1/8 LHC] Status of the LHC - Rencontres de Moriond

  18. LHC Hardware Commissioning • Commissioning of the magnets & circuits (power converter, quench protection, interlocks..) follows predefined test steps. • 1’700 circuits, 10’000 magnets • Commissioning time ~5 months • LHC commissioned for a beam energy of: • 2008: 5.5 TeV (5 TeV target for physics). • Issue with Magnet re-training required above ~6 TeV. • 2009: 1.2 TeV (incident, commissioning delays). • 2010: 3.5 TeV (limited by joint quality – see later). Status of the LHC - Rencontres de Moriond 11’122 test steps (2008) April September

  19. September 10th - control (show) room For 3 days all went perfectly well with beam… Status of the LHC - Rencontres de Moriond

  20. Outline Introduction Installation and preparation for beam Incident in sector 34 and repair LHC beam operation Conclusions Status of the LHC - Rencontres de Moriond

  21. Incident of Sept. 19th 2008 • On the beam startup date not all the circuits had been fully commissioning for 5 TeV beam operation. The last steps were completed a week later… • During the last commissioning step of the last main dipole circuit an electrical fault developed at ~5.2 TeV in the dipole bus bar at the interconnection between a quadrupole and a dipole magnet. • Later correlated to quench due to a local R ~220 nW – nominal 0.35 nW. • An electrical arc developed and punctured the helium enclosure. • Around 400 MJfrom a total of 600 MJ stored in the circuit were dissipated in the cold-mass and in electrical arcs. • Large amounts of Helium were released into the insulating vacuum. • The pressure wave due to Helium flow was the cause of most of the damage (collateral damage). Status of the LHC - Rencontres de Moriond

  22. Magnet Interconnection Melted by arc Status of the LHC - Rencontres de Moriond Dipole busbar

  23. Collateral damage Quadrupole-dipole interconnection Quadrupole support Status of the LHC - Rencontres de Moriond Sooth clad beam vacuum chamber • Main damage area covers ~ 700 metres. • 39out of 154 main dipoles, • 14 out of 47 main quadrupoles • from the sector had to be moved to the surface for repair (16) or replacement (37).

  24. Bus-bar joint • 24’000 bus-bar joints in the LHC main circuits. • 10’000 joints are at the interconnection between magnets. • They are welded in the tunnel. Status of the LHC - Rencontres de Moriond • Nominal joint resistance: • 1.6 K 300pΩ • 300K ~10μΩ For the LHC to operate safely at a certain energy, there is a limit to maximum value of the joint resistance.

  25. Welding Status of the LHC - Rencontres de Moriond

  26. Joint quality • The copper stabilizes the bus bar in the event of a cable quench (=bypass for the current while the energy is extracted from the circuit). • Protection system in place in 2008 not sufficiently sensitive. • A copper stabilizer with reduced continuity coupled to a superconducting cable badly soldered to the stabilizer may lead to a serious incident. Status of the LHC - Rencontres de Moriond Solder No solder X-ray of joint wedge • During repair work in the damaged sector, inspection of the joints revealed systematic voids caused by the welding procedure. bus U-profile bus

  27. LHC repair and consolidation 14 quadrupole magnets replaced 39 dipole magnets replaced 204 electrical inter-connections repaired Over 4km of vacuum beam tube cleaned Status of the LHC - Rencontres de Moriond New longitudinal restraining system for 50 quadrupoles Almost 900 new helium pressure release ports 6500 new detectors and 250km cables for new Quench Protection System to protect from busbar quenches Collateral damage mitigation

  28. Operating energy • Highest energy where LHC can be operated safely depends on: • Joint quality (max. excess resistance). • Quench propagation between magnets ( trigger of bus-bar quench). • Speed of energy extraction: time constant of current decay. • Based on models and experimental tests: • In the present situation the LHC cannot be operated above 3.5 TeV without taking a significant risk. • A major verification and repair campaign must be performed on all magnet interconnection to reach 7 TeV / beam – shutdown in 2012. Status of the LHC - Rencontres de Moriond >> LHC run 2010/2011 at 3.5 TeV / beam

  29. Outline Introduction Installation and preparation for beam Incident in sector 34 and repair LHC beam operation Conclusions Status of the LHC - Rencontres de Moriond

  30. Reserve slides 20thNovember 2009 • 14 months to repair, consolidate and re-commissioning all elements. • Energy limit at 1.2 TeV in 2009 due to additional work to make the new bus-bar quench protection system (nQPS) operational. • Great relief on November 20thwhen both beams circulated again !!! Status of the LHC - Rencontres de Moriond

  31. 2009 beam operation milestones Status of the LHC - Rencontres de Moriond • Many LHC systems were commissioned at forced pace – aim to check as much as possible. • Overall uptime ~60% - very good at this stage. • Our most optimistic dream plan became true !! • A touch of modesty… • The stored energy did not exceed 30 kJ – 0.01% of nominal.

  32. Beam optics • The magnetic model is in very good shape. • At 1.2 TeV the optics errors are within spec without any correction. • Work on optics at 450 GeV ongoing – almost fixed. Optics error (‘beta-beating’) at 450 GeV & 1.2 TeV Status of the LHC - Rencontres de Moriond Relative beam size error  (Db/b)   10% Specification

  33. Protons visible by eye • At the LHC momentum and magnetic fields are sufficiently strong for the protons to emit visible synchrotron light that can be used to image the beams in real-time. • The energy loss per turn is 7 keV at 7 TeV. Status of the LHC - Rencontres de Moriond

  34. Cleaning efficiency measurement • Full collimation setup at injection in 2009. • Beam cleaning efficiencies ≥ 99.98% ~ as designed Loss at primary collimator CLEANING Collimation Collimation Status of the LHC - Rencontres de Moriond Peak leakage to supercond. magnets Measurement noise

  35. … and simulation ‘Collimation leaks’ Status of the LHC - Rencontres de Moriond Observed level Observed level Observed level PHD C. Bracco (2009)

  36. Collisions at 450 GeV • Collisions were delivered to the experiments for a few days to collect data at 450 GeV for detector studies. • ~1.5 million events were collected by the LHC experiments • L ~ 1026 – 1027 Hz/cm2 Beam1 current Beam2 current Status of the LHC - Rencontres de Moriond 24 hours

  37. 1.2 TeV Collisions Transverse beam vertex reconstructed by CMS. Status of the LHC - Rencontres de Moriond • Thanks to very clean beam conditions, the experiments could record first collisions at 1.2 TeV. • But no full setup could be made for 1.2 TeV

  38. 2010-2011 run • (Ambitious) goal : collect 1 fm-1 of data/exp at 3.5 TeV/beam. • To achieve such a goal the LHC must operate in 2011 with • L ~ 21032 Hz/cm2 ~ TEVATRON L • which requires ~700 bunches of 108 p/bunch • (stored energy of ~ 30 MJ – 10% of nominal) Status of the LHC - Rencontres de Moriond • Implications: • Strict and clean machine setup. • Machine protection systems at near nominal performance. • ~2-4 weeks of commissioning time • Careful and step-wise increase of intensity, starting with just 4 bunches

  39. 2010-2011 planning • Jan-Feb 2010: commissioning of LHC circuits for 3.5 TeV operation. • Beam operation 2010: • Start-up with beam. • Consolidation at 450 GeV (optics…). • Ramp to 3.5 TeV. • Low intensity collisions at 3.5 TeV. • Interaction spot size squeezing. • Low intensity collisions at 3.5 TeV squeezed. • Stepwise (factor 2-4) increase of intensity to 1-2 MJ/ beam • Switch from individual bunches to bunch train operation (b separation 50 ns). • … • Lead ion run End February Today Status of the LHC - Rencontres de Moriond End March April Summer November

  40. (Possible) Luminosity evolution We have a reasonable scenario up to L ~ 1031 Hz/cm2 November mid-April Status of the LHC - Rencontres de Moriond Evolution in this regime of stored energy is difficult to predict Horizontal scale depends on real machine availability!

  41. Summary • The electrical incident 9 days after startup in 2008 revealed quality issues of the bus-bar joints. • 14 months of repair and re-commissioning. • New diagnostics for online monitoring and protection of all joints. • Eradication of joint issues requires a complete warm-up and long shutdown. • The LHC beam energy will be limited to 3.5 TeV in 2010/2011. • Long shutdown in 2012 to prepare LHC for 7 TeV / beam. • Very successful beam commissioning in 2009 to 1.2 TeV, now preparing for 18 months run at 3.5 TeV. • Aiming for luminosities up to ~1032 cm-2s-1 in 2010/11. • But the real beam challenges are ahead of us ! Status of the LHC - Rencontres de Moriond

  42. Spare slides Status of the LHC - Rencontres de Moriond

  43. LHC layout IR5:CMS experiment • 8 arcs (sectors) • 8 long straight sections (700 m long): • IR1 to IR8 • 2 separate vaccum chambers • beams cross in 4 points and exchange role in inner/outer ring IR4: Radio frequency system IR6: Beam dumping system Sector 34 Status of the LHC - Rencontres de Moriond IR3: Collimation IR7: Collimation IR8: LHC-B experiment IR2: ALICE experiment IR1: ATLAS experiment Injection Injection

  44. Pressure wave Status of the LHC - Rencontres de Moriond • Pressure wave propagates along the magnets inside the insulating vacuum enclosure. • Rapid pressure rise : • Self actuating relief valves could not handle the pressure. • designed for 2 kg He/s, incident ~ 20 kg/s. • Large forces exerted on the vacuum barriers (every 2 cells). • designed for a pressure of 1.5 bar, incident ~ 8 bar. • Several quadrupoles displaced by up to ~50 cm. • Connections to the cryogenic line damaged in some places. • Beam vacuum to atmospheric pressure.

  45. New quench protection system Joint resistance measurement example (at 1.9 K) R (nW) excess of 2 nW excess R Status of the LHC - Rencontres de Moriond expected R measured R Bus segment no.

  46. Operating energy Status of the LHC - Rencontres de Moriond

  47. 154 dipole magnets are connected as one circuit to the power converter. Time for the energy/field ramp is about 20-30 min (energy from the grid) Time for regular discharge (ramp down) is about the same (energy to the grid) Dipole magnets in arc cryostat DFB DFB Magnet 2 Magnet 4 Magnet 152 Magnet 154 Magnet 1 Magnet 3 Magnet 5 Magnet 153 Energy Extraction: switch closed Energy Extraction: switch closed Power Converter

  48. Bus-bar must carry the current during the discharge through interconnections Quench protection • Quench detected: energy stored in magnet dissipated inside the magnet (time constant of 200 ms). • Parallel diode becomes conducting: current of other magnets through diode. • Resistances are switched into the circuit: up to 1 GJ of energy is dissipated in the resistances (nominal decay time constant: 100 s). DFB DFB Magnet 2 Magnet 4 Magnet 152 Magnet 154 Magnet 1 Magnet 3 Magnet 5 Magnet 153 Energy Extraction: switch open Energy Extraction: switch open Power Converter

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