When the LHC and injector beams stopped on 16 February, the following words appeared on LHC Page 1: “No beam for a while. Access required: Time estimate ˜2 years”. This message marked the start of the first long shutdown (LS1). Over the coming years, major maintenance work will be carried out across the whole of CERN’s accelerator chain. Among the many tasks foreseen, more than 10,000 LHC magnet interconnections will be consolidated and the entire ventilation system for the 628-m-circumference Proton Synchrotron will be replaced, as will more than 100 km of cables on the Super Proton Synchrotron. The LHC is scheduled to start up again in 2015, operating at its design energy of 7 TeV per beam, with the rest of the CERN complex restarting in the second half of 2014.
The LHC’s first dedicated proton–lead run came to an end on 10 February, having delivered an integrated luminosity of more than 30 nb–1 to ALICE, ATLAS and CMS and 2.1 nb–1 to LHCb, with the TOTEM, ALFA and LHCf experiments also taking data. This run had ended later than planned because of challenges that had arisen in switching the directions of the two beams; as a result the 2013 operations were extended slightly to allow four days of proton–proton collisions at 1.38 TeV. To save time, these collisions were performed un-squeezed. After set up, four fills with around 1300 bunches and a peak luminosity of 1.5 × 1032 cm–2 s–1 delivered around 5 pb–1 of data to ATLAS and CMS. The requisite luminosity scans were somewhat hampered by technical issues but succeeded in the end, leaving just enough time for a fast turnaround and a short final run at 1.38 TeV for ALFA and TOTEM.
On 14 February, the shift crew dumped the beams from the LHC to bring to an end the machine’s first three-year physics run. Two days of quench tests followed immediately to establish the beam loss required to quench the magnets. Thanks to these tests, it will be possible to set optimum thresholds on the beam-loss monitors when beams circulate again in 2015.
Despite no beam from 16 February onwards, the LHC stayed cold until 4 March so that powering tests could verify the proper functioning of the LHC’s main magnet (dipole and quadrupole) circuits. At the same time, teams in the CERN Control Centre performed extensive tests of all of the other circuits, up to current levels corresponding to operation with 7 TeV beams. By powering the entire machine and then going sector by sector, the operators managed to perform more than a thousand tests on 540 circuits in just 10 days. Small issues were resolved by immediate interventions and the operators identified a number of circuits that need a more detailed analysis and possibly intervention during LS1.
With powering tests complete, the Electrical Quality Assurance team could test the electrical insulation of each magnet, sector by sector, before the helium was removed and stored. Beginning with sector 5–6, the magnets are now being warmed up carefully and the entire machine should be at room temperature by the end of May.
