On Friday, the LHC opened its doors to allow particles to travel around the ring for the first time since the year-end technical stop (YETS) began in December 2015. At 10:30 a.m., a first bunch was circulating and by midday the beam was circulating in both directions. Progress over the weekend has been good and low intensity beam has already been taken to 6.5 TeV and through the squeeze.
Last week, the LHC underwent the final phase of preparation before beam -known as the machine checkout. During this phase all the systems of the LHC are put through their paces without beam. A key part of the process is driving the magnetic circuits, radiofrequency accelerating cavities, collimators, transverse dampers etc. repeatedly through the nominal LHC cycle.
A full program of beam instrumentation checks took place to make sure that active elements were working and that the complex acquisition chain was functioning properly. Detailed checks were performed on the collimation systems.
The radiofrequency system was re-commissioned. The LHC beam dump system was subject to stringent operational checks. In parallel, a pilot beam extracted from the SPS was sent down the two SPS-LHC transfer lines to the beam dumps just before the start of the LHC proper.
While the machine checkout was ongoing, the experiments had been finishing their own last interventions before the closure of the caverns.
With the beams back in the rings, a phase of recommissioning with beam starts for the LHC. “The LHC team will work with low intensity beam for about 3 to 4 weeks to re-commission all systems and to check out all aspects of beam-based operation to make sure that the LHC is fully safe before ‘stable beams’ is declared,” explains Mike Lamont, head of the accelerators operation team. Stable beams is the signal that the experiments can start taking data.
2015 saw the start of Run 2 for the LHC during which the proton-proton collision energy reached 13 TeV. Beam intensity has increased and by the end of the 2015 run 2240 proton bunches per beam were being collided. This year, the aim is to increase the number of bunches even further to the target of 2748. The goal is to reach an integrated luminosity of around 25 inverse femtobarn (fb-1), up from the 4 fb-1 it reached by the end of last year. One fb-1 corresponds to around 80 million million collisions.