Risk analysis update of the LHC cryogenic system following the 19th September 2008 incident

On 19th September 2008, during powering tests of the main dipole circuit of the Large Hadron Collider, an electrical fault occurred producing an electrical arc and resulting in mechanical and electrical damage, release of helium from the magnet cold mass to the insulation vacuum enclosure and consequently to the tunnel, via the spring-loaded relief discs on the vacuum enclosure. The pressurization of the vacuum space exceeded significantly the allowed design value. Mathematical modeling based on a thermodynamic approach has enabled the revision of the helium discharge system protecting the vacuum enclosure against the over-pressurization in case of a redefined maximum credible incident (MCI) occurrence.