At a brief ceremony on 7 November deep in the LHC tunnel CERN's director-general, Robert Aymar, sealed the last interconnection between the collider's main magnet systems. This is the latest milestone in commissioning the LHC, which is scheduled to start up in 2008 (CERN Courier July/August 2007 p5). The ceremony marks the end of a two-year programme of work to connect all of the main dipole and quadrupole magnets in the machine, a complex task that included both electrical and fluid connections.

The 27 km circumference LHC is divided into eight sectors, each of which can be cooled down to the operating temperature of 1.9 K and powered up independently. The first sector was cooled down and powered up in the first half of 2007 and has now been warmed up for minor modifications. This was an important learning process, allowing subsequent sectors to be commissioned more quickly. Four more sectors will be cooling by the end of 2007 and the remaining three sectors that have not been cooled will begin the process early in 2008.

To cool the magnets, more than 10,000 tonnes of liquid nitrogen and 130 tonnes of liquid helium will be brought into use through a cryogenic system, which includes more than 40,000 leak-tight welds.

If all goes well, the first beams could be injected into the LHC in May 2008, and circulating beams established by June or July. With a project of this scale and complexity, however, the transition from construction to operation is a lengthy process. Every part of the system has to be brought on stream carefully, with each subsystem and component tested and repaired, if necessary. "If for any reason we have to warm up a sector, we'll be looking at the end of summer rather than the beginning," warns project leader Lyn Evans.