Last modified 5 years ago Last modified on 06/19/12 10:35:58

Decrypting LHC status

Glossary CP3 members: feel free to edit.

  • Access in ...: A physical intervention is needed, either on one detector or on some element of the machine (power supply, probe, magnet, ...). To ensure the security of the persons in the tunnel, no beam can circulate in such conditions. Procedures before and after the access itself also take time.
  • ADT:
  • Alice: A Large Ion Collider Experiment, one of the four main experiments at the LHC. Dedicated to heavy ion collisions. Located at Point 2.
  • ATLAS:A Toroidal LHC ApparatuS, one of the four main experiments at the LHC. General purpose experiment. Located at Point 1.
  • B1, B2 (B1 (1,17851) B2 (1,8911)): Beam 1 and 2 are the two beams circulating in opposite directions in the machine. Sometimes, the bucket containing protons is specified in parenthesis. Protons will collide only if the same bucket is filled in each beam.
  • Beam: One calls beam the set of protons circulating in one direction in the LHC. In practice, protons are grouped in bunches, but since one bunch does 10 millions turns per second, it looks continuous at our macroscopic scale.
  • Beta*: one of the parameters impacting the luminosity. Beta* gives the distance after which the beam size doubles.
  • BIS:
  • Booster: The booster is one accelerator used to pre-accelerate protons before sending them to the LHC. It is part of a long chain: Linac->Booster->PS->SPS->LHC.
  • Bucket: One calls bucket possible position for a bunch in the beam. This is a virtual accounting of the possible slots where protons can be injected. It counts from 1, is incremented every 25ns and is reset every orbit (each time the beam did one full turn).
  • Bunch: Packet of protons circulating together in the LHC. One bunch contains from 109 to 1011 protons. There are from 1 to few hundreds bunches per beam. In 2013, there will be up to 2808 bunches in each beam: one every 25ns.
  • Capturing the beam: Putting the protons in the machine and the accelerating cavities in sync, such that the beam is stabilized. Think like if you had to catch a thrown stone with a sling to make it then turn above you.
  • Cavity:
  • CERN: European Organization for Nuclear Research
  • CMS: Compact Muon Solenoid, one of the four experiments at the LHC. General purpose experiment. Located at Point 5.
  • Collimator (Moving collimators): mobile devices restricting the aperture of the machine. Moving the collimators closer to the beam one can remove the protons that are too far from the nominal orbit. By measuring the current on the collimators one can also monitor the beam position.
  • Collide: Term used to describe the interaction of protons from each beams.
  • Control room center (CC, CCC): Place from where the operators run the machine and the experiments.
  • Coupling:
  • Chromaticity (Non-linear [...]):
  • Cryogenics (Cryo start, lost cryo): cooling circuits ensuring a working temperature of 2 Kelvins for the LHC magnets.
  • Dipole magnet: Magnets used to bend the trajectory of protons and make them turn in the LHC.
  • Dump (Beam dump, emergency dump):
  • Emittance:
  • Excursion (Beam excursion): deviation of the beam w.r.t. the nominal orbit
  • Fill ([...] for Physics): Period in between injection and dump
  • Filling scheme (e.g.: 12b_8_8_8): configuration of bunches in the machine. The scheme is named using the number of bunches, the number of colliding bunches in CMS/ATLAS, the number of colliding bunches in Alice, the number of colliding bunches in LHCb, and eventually a free field for comments.
  • Flag (Beam flag):
  • Flat top: Period when the energy reached the maximal and stable value.
  • GeV (450 GeV): Unit of energy. 1GeV is the kinematic energy of a proton accelerated by a difference of potential of 1 gigaelectronvolt
  • Handshaking: Procedure between LHC and experiments before going into operations (Be prepared. I am preparing... Are you ready ? I am ready ! Here we go !!!).
  • HII: read 'Fill' (OCR confused).
  • Injection (Beam injection, injection permit by [exp], injection energy): procedure by which protons are put in the LHC ring.
  • Intensity: Number of protons in the beam.
  • Interlock (collimator [...]):
  • Intervention:
  • IP: interaction point, where the beams converge, where the bunches cross and the protons collide. Central point of the detectors.
  • Kicker: Magnet used to kick the beam out of the LHC when one wants to "dump the beam"
  • LBDS: beam current measurement devices
  • LHC: Large Hadron Collider
  • LHCb: Large Hadron Collider beauty experiment, one of the four main experiments at the LHC. Dedicated to CP violation. Located in Point 8.
  • Life-time (Beam [...]): beam intensity decreases ~exponentially. The beam lifetime is the time after which it is reduced to 1/e of its initial intensity.
  • Linac: First stage of the acceleration chain providing the LHC with particles.
  • Luminosity:
  • Magnet: Active compounents of the beamlines allowing to stear, focus and drive the beam particles. Magnets act on particle beams as lenses on optical beams.
  • Orbit correction:
  • Optimization:
  • Optics: set of magnets acting on the beamline.
  • Patrol: Security tour organized after access periods to make sure nobody is left in the area. By extension, the same name is given to the security system that ensures that no door is opened during operation, and that interlocks the beam in case. "We lost the patrol" means that one such sensor triggered, most often because of a faulty door. Nobody was ever lost in the tunnel ;)
  • Pattern (Bunch pattern): LHC beams are segmented in bunches of particles, which are not equidistant but structured in several sets. The arrangement of these bunches is called the pattern (see Filling scheme).
  • Piquet: On-call person to intervene 24/7 on some critical equipment.
  • Precycling: Bringing the machine to the state ready for injection. That implies removing the hysteresis in the magnets, after a previous operation.
  • Probes:
  • Physics fill: Run in stable good and controlled conditions for physics.
  • Piwinski angle:
  • Proton: LHC beams can be made of several types of hadrons. Proton beams are the main type of beams.
  • Point (Point 1, Point 5, ...): Along the LHC tunnel, 8 equidistant caverns are accessible from the surface. Four of them host the main experiments (ATLAS in Point 1, Alice in Point 2, CMS in Point 5, LHCb in Point 8). The other four host beam facilities (collimation in Point 3 and 7, acceleration cavities in Point 4, dumping in Point 6)
  • Post-mortem: record of the conditions that led to a beam abort.
  • PS: One of the small circular accelerators used for the LHC beam preparation. PS is located in the acceleration chain between the booster and the SPS.
  • Q':
  • Quench: transition from supraconductor state to conductor state for a magnet, caused by local energy deposit/heating or mechanical stress.
  • QPS: quench protection system
  • Quadripole magnet: magnet used to focalise and steer the beam
  • Ramp (energy ramp, ramping): increasing the beam energy by increasing the RF frequency and the magnet current.
  • Ramp down: decreasing the current in the magnets after a beam dump to return to injection conditions.
  • Ramp down-precycle combo: combination of a ramp down with the recycling procedure
  • RB:
  • Recycling: procedure that cycles the magnets to remove hysteresis after operation at high field.
  • RF: radio-frequency (used to capture and accelerate the beam)
  • RQT:
  • Scan (lumi scan):
  • Sector (S3, ..., S45, ...): the LHC is divided in 8 sectors.
  • Separation bumps (Collapsing [...]): removing the small kink given to beams to avoid collisions before nominal conditions.
  • Squeeze : reducing the beta* just before collisions.
  • SPS: One of the circular accelerators used for the LHC beam preparations. SPS receive particle bunches from the PS and deliver them to the LHC at a 450 GeV energy.
  • Stable beams: beams that are safe for detectors and that will not be manipulated further by the operators (no modification of colimators, magnets settings, energy, ...)
  • TeV (3.5, 7, 14 TeV): 1000 GeV, unit for energy, typical energy scale in high-energy physics, 1 TeV ~ 0.1 micro Joule
  • Till: often to be read as Fill, the Optical Character Recognition software has some troubles to disentangle t and f on the LHC status screen.
  • Triplet (Inner [...]): set of three quadrupoles located just before the experiments to do the final beam focalisation for collisions.
  • Tripped: went of due to over current.
  • Vacuum (vacuum sensor, vacuum leak):
  • Van der Meer scan: procedure to calibrate the luminosity measurement by scanning the beam profile.
  • Water problem: some problem with water (generally used for cooling electronics and some warm magnets)
  • Wirescan profile: Luminosity measurement method.

LHC Operations

Data / CMS

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Live events in CMS

Previous runs


LHC proton-proton Integrated Luminosity 2011 7 TeV


Integrated luminosity for LHC run in 2010 at 2x3.5TeV