Commissioning the LHC is making steady progress towards the target of achieving a complete cool down by the middle of June, allowing the first injection of beams soon after. This will come almost exactly 19 years after the start up of LEP, the machine that previously occupied the same tunnel. The LHC’s first collisions will follow later.
Half of the LHC ring – between point 5 and point 1 – was below room temperature by the first week of April, with sectors 5-6 and 7-8 fully cooled. The next step for these sectors will be the electrical tests and powering up of the various circuits for the magnets. From late April onwards, every two weeks the LHC commissioning teams will have a new sector cooled to 1.9 K and ready for testing.
Sector 7-8 was the first to be cooled to 1.9 K in April 2007, and the quadrupole circuits in the sector were powered up to 6500 A during the summer. The valuable experience gained here allowed the hardware commissioning team to validate and improve its procedures and tools so that electrical tests on further sectors could be completed faster and more efficiently. Each sector has 200 circuits to test.
The next electrical tests were carried out on sector 4-5 from November 2007 to mid-February 2008. Once the temperature had been stabilized at 1.9 K by the beginning of December, the circuits were powered up to an initial 8.5 kA. The main dipole circuit was then gradually brought up to 10.2 kA during the last week of January 2008, with the main quadrupole circuits reaching 10.8 kA in February. At this current the magnets are capable of guiding a 6 TeV proton beam.
During this testing of sector 4-5, however, a number of magnet-training quenches occurred for both dipole and quadrupole circuits. Three dipoles in particular quenched at below 10.3 kA, despite having earlier been tested to the nominal LHC operating current of 11.8 kA. It appears that retraining of some magnets will be necessary, which is likely to take a few more weeks. CERN’s management, with the agreement of all of the experiments and after having informed Council at the March session, decided to push for collisions at an energy of around 10 TeV as soon as possible this year, with full commissioning to 14 TeV expected to follow over the winter shutdown. Past experience indicates that commissioning to 10 TeV should be achieved rapidly, with no quenches anticipated.
Sector 5-6 will be the next to cross the 10 kA threshold; electrical tests here began in April. Sector 4-5, meanwhile, was warmed up again to allow mechanics to connect the inner triplet magnets, which were modified after a problem arose during pressure testing last year.
