Der LHC Beschleuniger - DPG - Bonn 1 Drawing by Sergio Cittolin Der LHC Beschleuniger: Herausforderungen auf dem Weg zu Teilchenkollisionen J. Wenninger CERN

Outline Der LHC Beschleuniger - DPG - Bonn 2 Introduction Installation and preparation for beam Incident in sector 34, repair and consequences LHC beam operation Conclusions

Der LHC Beschleuniger - DPG - Bonn The Large Hadron Collider LHC 3 CMS, Totem ATLAS, LHCf LHCbLHCb ALICEALICE Lake of Geneva Installed in 26.7 km LEP tunnel Depth of m Control Room LHC ring SPS ring

ATLAS Der LHC Beschleuniger - DPG - Bonn 4

CMS Der LHC Beschleuniger - DPG - Bonn 5

LHCb Der LHC Beschleuniger - DPG - Bonn 6

ALICE Der LHC Beschleuniger - DPG - Bonn 7

TOTEM and LHCf Der LHC Beschleuniger - DPG - Bonn 8 Total X-section, elastic and diffractive scattering. Forward production of neutral particles (cosmic ray shower modeling)

Collider luminosity Der LHC Beschleuniger - DPG - Bonn 9 “Thus, to achieve high luminosity, all one has to do is make (lots of) high population bunches of low emittance to collide at high frequency at locations where the beam optics provides as low values of the amplitude functions as possible.” PDG 2005, chapter 25  Parameters: –Number of particles per bunch  –Number of bunches per beamk b –Beam sizes at the collision point  –Revolution frequencyf –Crossing angle factorF ~ 1 Collision rate is proportional to luminosity Interaction Region Beam quality (emittance) Intensity

LHC challenges Der LHC Beschleuniger - DPG - Bonn 10 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 field8.3 T HERA/Tevatron ~ 4 T  The luminosity of the collider that will reach unprecedented values for a hadron machine: LHC pp ~ cm -2 s -1 Tevatron pp3x10 32 cm -2 s -1 SppSpp6x10 30 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 A factor 30 in luminosity

LHC dipole magnet Der LHC Beschleuniger - DPG - Bonn 11  1232 dipole magnets.  B field 8.3 T ( K (super-fluid Helium)  2 magnets-in-one design : two beam tubes with an opening of 56 mm.  Operating challenges: o Dynamic field changes at injection. o Very low quench levels (~ mJ/cm 3 )

Stored energy Der LHC Beschleuniger - DPG - Bonn 12 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 Damage threshold

Collimation Der LHC Beschleuniger - DPG - Bonn 13 beam 1.2 m  To operate at nominal performance the LHC requires a large and complex collimation system o Previous colliders used collimators mostly for experimental background conditions.  Ensure ‘cohabitation’ of: o 360 MJ of stored beam energy, o super-conducting magnets with quench limits of few mJ/cm 3  Almost 100 collimators and absorbers.  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.

Outline Der LHC Beschleuniger - DPG - Bonn 14 Introduction Installation and preparation for beam Incident in sector 34, repair and consequences LHC beam operation Conclusions

Installation Der LHC Beschleuniger - DPG - Bonn 15  Transport in the tunnel with an optically guided vehicle.  Approximately 1600 magnet assemblies transported over up to 20 km at 3 km/hour.  First dipole lowered March Magnet installation until spring 2007 Interconnection work finished end 2007

3 km long arc cryostat Der LHC Beschleuniger - DPG - Bonn 16

LHC cool-down Der LHC Beschleuniger - DPG - Bonn 17 Cool-down time to 1.9 K is nowadays ~4 weeks/sector [sector = 1/8 LHC] All sectors at nominal temperature First beam around the LHC

LHC Hardware Commissioning Der LHC Beschleuniger - DPG - Bonn 18  Commissioning of the magnets & circuits (power converter, quench protection, interlocks..) follows predefined test steps. 1’700 circuits, 10’000 magnets Commissioning time ~5 months 11’122 test steps (2008) AprilSeptember

September 10 th - control (show) room Der LHC Beschleuniger - DPG - Bonn 19 For 3 days all went perfectly well with beam…

Outline Der LHC Beschleuniger - DPG - Bonn 20 Introduction Installation and preparation for beam Incident in sector 34, repair and consequences LHC beam operation Conclusions

Incident of Sept. 19 th Der LHC Beschleuniger - DPG - Bonn 21 The final circuit commissioning was performed in the week following the startup with beam.  During the last commissioning step of the last main dipole circuit an electrical fault developed at ~5.2 TeV (8.7 kA) in the dipole bus bar (cable) at the interconnection between a quadrupole and a dipole magnet. Later correlated to quench due to a local R ~220 n  – nominal 0.35 n   An electrical arc developed and punctured the helium enclosure. 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. The pressure wave due to Helium flow was the cause of most of the damage (collateral damage).

Magnet Interconnection Der LHC Beschleuniger - DPG - Bonn 22 Dipole busbar Melted by arc

Collateral damage Der LHC Beschleuniger - DPG - Bonn 23 Quadrupole-dipole interconnection Quadrupole support Main damage area covers ~ 700 metres.  39 out 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). Sooth clad beam vacuum chamber

Bus-bar joint Der LHC Beschleuniger - DPG - Bonn 24  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. Nominal joint resistance: 1.9 K 0.3 nΩ 300K ~10 μΩ For the LHC to operate safely at a certain energy, there is a limit to maximum value of the joint resistance.

Joint quality Der LHC Beschleuniger - DPG - Bonn 25 bus U-profile bus wedge SolderNo solder  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 bus bar with reduced continuity coupled to a superconducting cable badly soldered to the stabilizer can lead to a serious incident.  During repair work in the damaged sector, inspection of the joints revealed systematic voids caused by the welding procedure. X-ray of joint

LHC repair and consolidation Der LHC Beschleuniger - DPG - Bonn quadrupole magnets replaced 39 dipole magnets replaced 204 electrical inter- connections repaired Over 4km of vacuum beam tube cleaned 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

LHC target energy: the way down Der LHC Beschleuniger - DPG - Bonn TeV Summer TeV Spring TeV Nov GeV Detraining nQPS 2 kA 6 kA 9 kA WhenWhy 12 kA Late 2008 Joints 1.18 TeV Design  All main magnets commissioned for 7TeV operation before installation  Detraining found when hardware commissioning sectors in 2008 –5 TeV poses no problem –Difficult to exceed 6 TeV  Machine wide investigations following S34 incident showed problem with joints  Commissioning of new Quench Protection System (nQPS)

LHC target energy: the way up Der LHC Beschleuniger - DPG - Bonn 28  Train magnets –6.5 TeV is in reach –7 TeV will take time  Repair joints  Complete pressure relief system  Commission nQPS system 2014 ? 2010 Training Stabilizers nQPS WhenWhat 7 TeV 3.5 TeV 1.18 TeV 450 GeV TeV

Outline Der LHC Beschleuniger - DPG - Bonn 29 Introduction Installation and preparation for beam Incident in sector 34, repair and consequences LHC beam operation Conclusions

Reserve slides Der LHC Beschleuniger - DPG - Bonn th November 2009  14 months to repair, consolidate and re-commissioning all elements.  Great relief on November 20 th when both beams circulated again !!!

2009 beam operation milestones Der LHC Beschleuniger - DPG - Bonn th Nov Day 0Both beams circulating after 6 hours 23 rd Nov Day 3First pilot collisions at 450 GeV 29 th Nov Day 9Beams ramped to 1.18 TeV 6 th Dec Day 16Stable 450 GeV for the experiments 8 th Dec Day 18Both beams ramped to 1.18 TeV – first collisions  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 plan became true !!  A touch of modesty… o The stored energy did not exceed 30 kJ – 0.01% of nominal.

Protons visible by eye Der LHC Beschleuniger - DPG - Bonn 32  At the LHC momentum and magnetic fields are sufficiently strong for the protons to emit visible light that can be used to image the beams in real-time. The energy loss per turn is 7 keV at 7 TeV.  Excellent performance of the beam instrumentation has largely contributed to the fast progress. Synch. light Flying wire LHC Flying wire SPS (injector)

Noise on the beam Der LHC Beschleuniger - DPG - Bonn 33  The beam is frequently self-excited, driven by noise ‘humps’ visible on the vertical beam oscillation spectrum. Amplitude of ~nm to  m. Source is still unknown. Cause of emittance (beam size) blow up.

Beam optics Der LHC Beschleuniger - DPG - Bonn 34  The magnetic model is in very good shape.  At 1.2 TeV the optics errors are within spec without any correction. Work on 450 optics corrections are ongoing Relative beam size error   (  Specification Initial optics error (‘beta-beating’) at 450 GeV & 1.2 TeV

Cleaning efficiency measurement Der LHC Beschleuniger - DPG - Bonn Measurement noise Peak leakage to supercond. magnets Loss at primary collimator  Full collimation setup at injection in  Beam cleaning efficiencies ≥ 99.98% ~ as designed 35 CLEANING Collimation

Beam dump Der LHC Beschleuniger - DPG - Bonn 36 Extraction kickers Dilution kickers Extraction septum magnets Dump block  Complex beam dumping system commissioned. Beam swept over dump surface (power load)

Collisions at 450 GeV Der LHC Beschleuniger - DPG - Bonn 37  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 LHC experiments. Beam1 current Beam2 current 24 hours

1.2 TeV Collisions Der LHC Beschleuniger - DPG - Bonn 38  With very clean beam conditions, the experiments could record first collisions at 1.2 TeV.

run Der LHC Beschleuniger - DPG - Bonn 39  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  Hz/cm 2 ~ Tevatron Luminosity which requires ~700 bunches of 10 8 p/bunch (stored energy of ~ 30 MJ – 10% of nominal)  Implications: o Strict and clean machine setup. o 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

Der LHC Beschleuniger - DPG - Bonn 40  Jan-Feb 2010: commissioning of LHC circuits for 3.5 TeV operation.  Beam operation 2010: o Start-up with beam. o Consolidation at 450 GeV (optics…). o Ramp to 3.5 TeV. o Low intensity collisions at 3.5 TeV. o Interaction spot size squeezing. o Low intensity collisions at 3.5 TeV squeezed. o Stepwise (factor 2-4) increase of intensity to 1-2 MJ/ beam o Switch from individual bunches to bunch train operation (b separation 50 ns). o … o Lead ion run End February End March April Summer Today November

A possible scenario Der LHC Beschleuniger - DPG - Bonn 41 mid-April November Evolution in this regime of stored energy will depend on actual experience – difficult to predict

Summary Der LHC Beschleuniger - DPG - Bonn 42  The 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.  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 (repair of all joints).  Very successful beam commissioning in 2009 to 1.2 TeV. Very fast commissioning pace.  Now preparing for 18 months run at 3.5 TeV. Aiming for luminosities up to ~10 32 cm -2 s -1 The beam challenges are ahead of us !