Terms and abbreviations used across this site, the analysis code and the test specifications. Grouped rather than alphabetical, because most of them only make sense next to their neighbours.
The machine
Term
Meaning
Superconducting circuit
A chain of magnets powered as one electrical unit, together with its power converter, current leads and protection equipment. The LHC has more than 1500 of them.
Quench
The loss of superconductivity in a magnet. The affected section becomes resistive and starts dissipating the circuit’s stored energy as heat; uncontrolled, it destroys the magnet.
RB
Main dipole circuit, 13 kA. Eight of them, one per sector. The dipoles bend the beam around the ring.
RQ / RQD / RQF
Main quadrupole circuits, 13 kA. Sixteen in total, powered as focusing (RQF) and defocusing (RQD) pairs. Quadrupoles focus the beam.
IPD
Individually Powered Dipole — the beam separation dipoles, D1 to D4.
IPQ
Individually Powered Quadrupole.
IT
Inner Triplet — the final focusing quadrupoles either side of an experiment.
600 A / 80-120 A / 60 A circuits
Corrector magnet circuits, named by their nominal current. There are many hundreds; some 600 A circuits have their own energy extraction system.
Busbar
The superconducting bus connecting magnets within a circuit. Its resistance is a monitored indicator of splice quality.
Splice
A joint between two superconducting cables. Splice resistance is measured during splice-mapping tests.
Current lead
The transition carrying current from room temperature into the cold circuit.
Protection
Term
Meaning
QPS
Quench Protection System. Detects the resistive transition and triggers protection.
QDS
Quench Detection System — the detection part of the QPS.
PIC
Powering Interlock Controller. Distributes interlocks between the protection systems and the power converter.
PC
Power Converter. Drives current into the circuit, and stops on command.
EE
Energy Extraction. Opens switches to divert circuit current into a dump resistor so the stored energy decays under control rather than into the quenched magnet.
QH
Quench Heater. Fired on detection to spread the quench through the magnet, so its energy is dissipated over a large volume instead of one spot.
FPA
Fast Power Abort. An abrupt, protective shutdown of a circuit’s powering.
SPA
Slow Power Abort. A controlled ramp-down.
SOF
Switch Opening Failure — in 600 A energy extraction, the case where the Z capacitor does not open during the event.
Circuit Quench Loop / Discharge Loop
The two hardware loops linking QPS, PIC, PC and EE. The first carries the healthy-state chain, the second the command to dump stored energy.
Testing
Term
Meaning
HWC
Hardware Commissioning. The campaign, each shutdown or technical stop, in which every circuit is re-tested before beam returns. Written HWC’25 for the 2025 campaign.
Powering test
A test in which a circuit is powered through a defined current profile while its protection systems are exercised and the resulting signals recorded.
MP3
The team responsible for the powering and protection of the superconducting circuits, and the audience for most SigMon results.
AccTesting
The system that schedules HWC tests, tracks campaign progress and collects expert signatures.
HWC Sequencer
Drives the hardware through a test sequence on AccTesting’s instruction.
Signature
An expert’s formal acceptance of a test result. SigMon returns the signatures a test is expected to receive.
PCC / PIC2 / PLI / PLIS / PNO / PXX
Powering test families. PCC checks converter configuration, PIC2 the interlock paths, PLI runs at intermediate current levels, PLIS at splice-mapping current, PNO at nominal. PXX analyses cover a family of tests differing only in target current and trigger source.
The named current levels a test ramps to — from minimum operating current, through injection and intermediate levels and splice-mapping current, up to nominal and beyond.
Technical Stop
A short planned interruption of beam operation during a run, used for maintenance and re-testing.
Data and tools
Term
Meaning
PM
Post Mortem. Stores a high-rate snapshot of signals around a critical event.
NXCALS
The continuous logging system, recording at a lower rate than PM but without gaps.
Buffer
One recorded PM signal trace for one event.
SWAN
CERN’s hosted Jupyter service, where SigMon’s analysis notebooks are published for experts to run.
Acc-Py
CERN’s Python package index, where the SigMon packages are released.
CCC
CERN Control Centre. Home of the integrated applications operators use to watch systems during a run.
DPP
CERN’s event-driven data processing platform. SigMon is moving to it so analyses react to Post Mortem events as they are recorded.
S3
CERN’s object storage service, where generated HTML reports are kept.
papermill / nbconvert
Tools for running a notebook with injected parameters and converting the result to HTML.
pyeDSL
The embedded query language in lhc-sm-api. Its QueryBuilder gives PM and NXCALS a single, readable query syntax.