The LHC is a giant scientific instrument built at the European Laboratory for Particle Physics (CERN).
It is built to accelerate, store and collide high energy proton beams.
This takes place in an a 27km-long ring in an underground tunnel beneath the French-Swiss border.
The collisions will be observed at various experiments built around the ring,
including ATLAS which RHUL is involved in. The eagerly anticipated re-start of LHC collisions is due in November 2009.
For more information, see http://public.web.cern.ch/Public/en/LHC/LHC-en.html.
Control Engineering article on LHC