LHC magnet quench incident (2008)
Days after the LHC's first particle beams circulated, a faulty electrical connection between two superconducting dipole magnets caused a quench. The energy release vaporized helium, ruptured the vacuum, and damaged 53 magnets along a kilometer of tunnel.
Repairs took over a year; the LHC restarted in November 2009 instead of September 2008.
The incident forced CERN to install safety systems that now guard every magnet circuit.
Superconducting systems fail fast and cost months. The new niobium-tin magnets carry the same class of risk.
