1 / 75

Status of the LHC

Status of the LHC. J. Wenninger CERN Beams Department Operation Group. Evian – 19 th October 2009. Outline. Recap of 2008 Incident in sector 34 The joint problems Repair and consolidation 2009/10 LHC run Conclusions. LHC Layout. IR5 :CMS experiment. 8 arcs (sectors)

randolphj
Download Presentation

Status of the LHC

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Status of the LHC J. Wenninger CERN Beams Department Operation Group Status of the LHC - Evian - J. Wenninger Evian – 19th October 2009

  2. Outline Recap of 2008 Incident in sector 34 The joint problems Repair and consolidation 2009/10 LHC run Conclusions Status of the LHC - Evian - J. Wenninger

  3. 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 IR3: Collimation Status of the LHC - Evian - J. Wenninger IR7: Collimation IR8: LHC-B experiment IR2: ALICE experiment IR1: ATLAS experiment Injection Injection

  4. 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 - Evian - J. Wenninger

  5. 2008 Recap Status of the LHC - Evian - J. Wenninger

  6. First beam around the LHC All sectors at nominal temperature LHC Cool-down in 2008 Cool-down time to 1.9 K ~ 4-6 weeks/sector [sector = 1/8 LHC] Status of the LHC - Evian - J. Wenninger

  7. LHC Hardware Commissioning • April to September 2008: • Commissioning of the magnets & electrical circuits (power converter, quench protection, interlocking..) following predefined test steps. • 1’700 circuits, 10’000 magnets • LHC was (almost) commissioned to 5.5 TeV (5 TeV target for physics in 2008). • Magnet re-training required above ~6 TeV (Noel magnets). Status of the LHC - Evian - J. Wenninger 11’122 test steps

  8. Injection tests • August – September 2008: • Injection tests of up to 4 adjacent sectors. • Almost all HW systems involved in tests. • Essential checks for: • Control system. • Beam instrumentation. • Optics (magnetic model) and aperture. Status of the LHC - Evian - J. Wenninger 22nd – 24th of August Evening of August 8th 2008: First beam in the LHC after ~25 years of design and construction. 8th – 10th of August 5th – 7th of September

  9. September 10th - control (show) room We hope that this year there will be fewer tourists…. Status of the LHC - Evian - J. Wenninger

  10. Beam threading • Threading by sector: • One beam at the time & one hour per beam. • Collimators used to intercept the beam (1 bunch, 2109 p - 2% of nominal bunch). • Beam through 1 sector (1/8 ring), correct trajectory, open collimator and move on. Beam 2 threading Status of the LHC - Evian - J. Wenninger

  11. Beam commissioning progress • September 10th : • 10:30 : Beam 1 around the ring (in ~ 1 hour). Beam makes ~ 3 turns. • 15:00 : Beam 2 around the ring, beam makes 3-4 turns. • 22:00 : Beam 2 circulates for hundreds of turns… • September 11th : • Late evening: Beam 2 captured by RF. • First emergency dump correctly executed. • September 12th : • All base instrumentation operational for beam position, intensity, losses. • Good beam lifetime (> 1 hour). • Optics measured. Status of the LHC - Evian - J. Wenninger

  12. September 19th Incident Status of the LHC - Evian - J. Wenninger

  13. Event sequence on Sept. 19th • On Sept 10th commissioning of the magnets to 5 TeV was not finished… • Completed between Sept 14th and Sept 19th (cryogenic problems…). • Last commissioning step of the main dipole circuit in sector 34 : • >> ramp to 9.3kA (5.5 TeV). • At 8.7kA an electrical fault developed in the dipole bus bar located in the interconnection between quadrupole Q24.R3 and the neighboring dipole. • Later correlated to a local resistance of ~220 nW – nominal value 0.35 nW. • An electrical arc developed which punctured the helium enclosure. • Secondary arcs developed along the arc. • Around 400 MJ from 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. • In total 6 tons of He were released. Status of the LHC - Evian - J. Wenninger

  14. Inter-connection Status of the LHC - Evian - J. Wenninger Vac. chamber Dipole busbar

  15. Pressure wave Status of the LHC - Evian - J. Wenninger • 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.

  16. Incident location Status of the LHC - Evian - J. Wenninger Dipole bus bar

  17. Collateral damage : displacements Quadrupole-dipole interconnection (27R3) Quadrupole support Status of the LHC - Evian - J. Wenninger • Main damage area ~ 700 metres. • 39out of 154 dipoles, • 14 out of 47 quadrupole short straight sections (SSS) • from S34 had to be moved to the surface for repair (16) or replacement (37).

  18. Collateral damage : beam vacuum Beam vacuum affected over entire 2.7 km length of the arc. Beam screen contaminated with sooth. Beam screen with clean Copper surface. Beam screen contaminated with multi-layer magnet insulation debris. Status of the LHC - Evian - J. Wenninger  60% of the chambers  20% of the chambers

  19. Schematic of the main dipole circuit Local (quench) protection of each magnet Status of the LHC - Evian - J. Wenninger Global protection of the bus-bar and bus-bar joints (splices) between magnets. Protection threshold 1 V (160 V inductive voltage during ramp). Bus-bar must cope with 100 second discharge time of circuit.

  20. Bus-bar joint • Superconducting cable embedded in Copper stabilizer. • Bus bar joint is welded (not clamped). • Joint resistance ~0.35 nW (@ 1.9 K). • Protected by global bus-bar protection system, no bypass diode. • relies on good quality of the joint. Status of the LHC - Evian - J. Wenninger • Visual inspection after welding. • For the new joints (repair) the resistance is measured at room temperature to qualify the joint.

  21. One of ~1700 bus-bar connections Status of the LHC - Evian - J. Wenninger

  22. Busbar welding Status of the LHC - Evian - J. Wenninger

  23. Bad electrical & thermal contact Likely incident cause : poor quality joint • Cryogenic temperature data indicated a local anomalous resistance ~220 nWin the cell where the incident occurred. • Joint model with poor electrical contact, R ~ 220 nW. • Simulation of the last ‘fatal’ ramp: thermal run-away around 8700 A. • Protection threshold of 1 V is not adequate for bad quality joints (Ok for quench with good joint !). • Threshold of ~0.3 mVis required to adequately protect the bus-bar against such incidents. Status of the LHC - Evian - J. Wenninger Localized non-sc zone Busbar quench

  24. The ‘joint story’ Status of the LHC - Evian - J. Wenninger

  25. Joint story part 1Search for anomalous resistances in the cold machine Status of the LHC - Evian - J. Wenninger

  26. Calorimetric data • Logged cryogenic data revealed a temperature anomaly of some 40 mK in the cell of the incident during a previous (lower current) powering cycle. • Interpretation can be tricky (He valves control loops) • Data from other powering tests indicated the presence of another anomaly in sector 12. Calorimetry suggested a ~100 nW resistance. 7 kA test on Sector 34 9.3 kA test on Sector 12 DT (mk) Status of the LHC - Evian - J. Wenninger +40 mK 4.1 TeV 5.5 TeV Temp keeps rising! Relative temperature, increase from 1.9 K Current in kA Suspicious cell in S12 : ~100 nWexcess 1 hour

  27. Calorimetric and electrical measurements • New diagnostics methods were developed: • Calorimetric measurement techniques with the possibility to localize anomalous resistances down to ~40 nW within a cryogenic cell. • >> Systematic calorimetric tests were launched on all available sectors • High precision voltage measurements were employed to measure all interconnection resistances (resolution < 1 nW) in suspected cells. • The existing quench protection data, averaged over long time intervals, was used to localize magnets with abnormal internal resistances (7 internal joints/magnet). Does not cover the magnet interconnections. • Outcome of the test campaign: • 2 magnets were localized with internal resistances of 50 and 100 nW. • - Both magnets had been tested to 12.4 kA (5% over nom.) before installation! Status of the LHC - Evian - J. Wenninger

  28. Electrical measurements 60min @ 7kA Voltage 10min @ 6kA,5kA,4kA,…,0kA R ~ 50 nW Status of the LHC - Evian - J. Wenninger “Snapshots” of high statistics voltage data collection from quench protection system Current (max = 7000 A)

  29. Status of joint checks end of 2008 Status of the LHC - Evian - J. Wenninger (1) suspected cases from calorimetric measurements 1 confirmed cases by electrical measurement.

  30. Where’s the solder? • The dipole with internal resistance of 50 nW was stress tested: • No aging (change of R) was observed on the test benches. • The dipole with internal resistance of 100 nW was opened: • Lack of solder on joint, not properly brazed. Status of the LHC - Evian - J. Wenninger

  31. Joint story part 2Silent killers Status of the LHC - Evian - J. Wenninger

  32. Joint quality • Careful inspection of all joints was performed when sector 34 was repaired, including systematic X-rays of interconnections. • The repair team had bad surprises: • Overheating leading to SnAg solder flowing out of the busbar and leaving empty spaces. B25R3-M3 before disconnection Status of the LHC - Evian - J. Wenninger Courtesy C. Scheuerlein

  33. Joint quality • Under heating and partly un-melted SnAg foils. Status of the LHC - Evian - J. Wenninger Such joint problems can be detected by a resistance measurement at room temperature: excess of some ten’s of mW.

  34. What is exactly the problem? • To understand how a poor joint quality affects the machine safety, one has to look at the magnet protection system…. Status of the LHC - Evian - J. Wenninger

  35. Super-conducting magnet quench • A ‚quench‘ is the phase transition from the super-conducting to the normal conducting state. • Quenches are initiated by an energy in the order of few mJ • movement of the superconductor (friction and heat dissipation), • beam losses, • cooling failures, • any other heat sources... • When part of a magnet quenches, the conductor becomes resistive, which can lead to excessive local energy deposition due to the appearance of Ohmic losses. To protect the magnet: • the quench must be detected. • the energy in the magnet /electrical circuit must be extracted. • the magnet current has to be switched off within << 1 second. LHC Status - Planck09 - Padova,IT An energy density of ~1 mJ/cm3is sufficient to destroy super-conductivity in a magnet (quench) : a local loss of 1 ppm of the beam is sufficient !

  36. Dipole magnets in arc cryostat • 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) 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

  37. Dipole magnet 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 (current decay time constant of 100 s). Bus-bar must carry the current for some minutes, through interconnections 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

  38. Normal interconnect, normal operation • Everything is at 1.9 Kelvin. • Current passes through the superconducting cable. • For 7 TeV : I = 11’800 A Magnet Magnet Helium bath copper bus bar 280 mm2 copper bus bar 280 mm2 superconducting cable with about 12 mm2 copper current Interconnection joint (soldered) This illustration does not represent the real geometry

  39. Normal interconnect, quench • Quench in adjacent magnet or in the bus-bar. • Temperature increase above ~ 9 K. • The superconductor becomes resistive. • During the energy discharge the current passes for few minutes through the copper bus-bar. Magnet Magnet copper bus bar 280 mm2 copper bus bar 280 mm2 superconducting cable interconnection

  40. Non-conform interconnect, normal operation • Interruption of copper stabiliser of the bus-bar. • Superconducting cable at 1.9 K • Current passes through superconductor. Magnet Magnet copper bus bar 280 mm2 copper bus bar 280 mm2 superconducting cable interconnection

  41. Non-conform interconnect, quench. • Interruption of copper stabiliser. • Superconducting cable temperature increase above ~9 K and cable becomes resistive. • Current cannot pass through copper and is forced to pass through superconductor during discharge. Magnet Magnet copper bus bar 280 mm2 copper bus bar 280 mm2 superconducting cable interconnection

  42. Non-conform interconnect, quench. • The superconducting cable heats up because of the combination of high current and resistive cable. Magnet Magnet copper bus bar 280 mm2 copper bus bar 280 mm2 superconducting cable interconnection

  43. Non-conform interconnect, quench. • Superconducting cable melts and breaks if the length of the superconductor not in contact with the bus bar exceeds a critical value and the current is high. • Circuit is interrupted and an electrical arc is formed. Magnet Magnet copper bus bar 280 mm2 copper bus bar 280 mm2 superconducting cable interconnection • Depending on ‘type’ of non-conformity, problems appear: • at different current levels. • under different conditions (magnet or bus bar quench.. ).

  44. September 19th hypothesis • Anomalous resistance at the joint heats up and finally quenches the joint. • Current sidesteps into Copper that eventually melts because the electrical contact is not good enough. Magnet Magnet copper bus bar 280 mm2 copper bus bar 280 mm2 superconducting cable quench at the interconnection >> New quench protection system was designed and installed to monitor and protect the busbars against such incidents in the future,

  45. Joint problem summary • Case A: Anomalous resistance within the joint when the magnets are at 1.9 K that may lead to S34 type accidents (bad soldering of the 2 busbar cables). • Detectable at 1.9 K with an upgrade of the quench detection and protection system. • Case B: Poor joint quality (voids…) that do not pose an immediate threat, but can lead to an S34 incident in the event of a nearby quench (busbar or magnet). • Detectable at room temperature with a resistance measurement. Status of the LHC - Evian - J. Wenninger B B A

  46. Joint measurement campaigns • Case B joint problem measurement campaigns: • Non-invasiveglobal DC measurements (sector closed and under vacuum) of the sector. • DC resistance of segments (busbar + number of joints) using signal taps. • Sector is ready for commissioning (all interconnects closed, vacuum…). • Works only reliably for dipoles and at room temperature. • Invasive measurements of the local joint: • DC resistance. • Ultrasound imaging. • X-ray imaging. • Interconnection must be opened (sector at room temp, vacuum broken…). Status of the LHC - Evian - J. Wenninger

  47. Non-invasive measurements Status of the LHC - Evian - J. Wenninger • 80 K measurements have large errors (much smaller Copper resistance)

  48. Invasive measurements • Those measurements were made if an interconnect was open (for repair…) or from strong evidence from a global measurement. • Dipoles: • 136 joints measured, 43 were found excessive • Quadrupoles: • 120 joints measured, 14 joints found excessive R (mW) Status of the LHC - Evian - J. Wenninger Meas. number Nominal R = 16 mW

  49. ‘Safe’ energy for 2009/10 run • The energy at which the LHC can be operated safely is determined by a number of factors: • Maximum additional joint resistance (wrt nominal value). • - recommendation: 90 mW (measurement uncertainties). • Copper resistance (RRR value, resistance ratio 300K/4.2K). • - recommendation : RRR = 120 • Quench propagation (time) from magnet to busbar. • Discharge time of the circuits. • - dipole : reduced from 103 s to 50 s • - quads : reduced from 15 s to 10 s • >> sets an absolute max of 5 TeV (induced voltage during discharge) • Simulations of direct busbar quenches by the beam. • - not a problem (geometry and loss monitor protection) Status of the LHC - Evian - J. Wenninger

  50. Simulations for dipoles Status of the LHC - Evian - J. Wenninger 3.5 TeV Courtesy A. Verweij

More Related