LHC report: Run 1 - the final flurry

The proton-lead run ended early on the morning of Sunday, 10 February. The run can be considered an unqualified success and a testament to the painstaking preparation by the ion team. It was followed by a few short days of proton-proton collisions at intermediate energy, after which the final physics beams of what is now being called Run 1 (2009 – 2013) were dumped at 7.24am on Thursday, 14 February.

The five weeks of operations originally scheduled for 2013 had two main objectives: the delivery of 30 inverse nanobarns with proton-lead collisions; and around 5 inverse picobarns of proton-proton collisions at a beam energy of 1.38 TeV. Both of these objectives were met.

As described in previous reports, the proton-lead run has gone remarkably well for a completely novel operational mode. However, there were some issues following the switch of beam direction on Friday, 1 February. In this exercise the ions become the clockwise beam and the experiments received lead-proton instead of proton-lead collisions. Although the issues, related to excessive beam losses in the squeeze with the two beams on markedly different orbits, were eventually resolved, the delay put the proton-proton run in jeopardy. The decision was thus made to extend 2013 operations by another 3 days.

Over 30 inverse nanobarns were delivered to ALICE, ATLAS and CMS during the proton-lead run, with 2.1 inverse nanobarns delivered to LHCb. Data was also taken by the TOTEM, ALFA and LHCf experiments. ALICE’s polarity was switched once, beam directions were changed, and luminosity calibrations were performed, as usual, with Van der Meer scans.

The proton-lead run was followed by four short days of proton-proton collisions at 1.38 TeV. To save time, these collisions were performed un-squeezed. After set-up, 4 fills with around 1300 bunches and a peak luminosity of 1.5 x1032 cm-2s-1 delivered around 5 inverse picobarns of data to ATLAS and CMS. The requisite luminosity scans were somewhat hampered by technical problems but in the end passed off successfully, leaving just enough time for a fast, frenzied turnaround and a short final run at 1.38 TeV for ALFA and TOTEM.

Two days of quench tests began immediately after the final physics beams were dumped on Thursday, 14 February. The tests aim to establish what beam loss is actually required to quench the magnets. This will allow optimum beam loss monitor thresholds to be set when beams circulate again in 2015. Operations with circulating beams have been remarkably quench-free so far.

The LHC and injectors will stop beams at 9am on Saturday, 16 February, with the LHC staying cold until 4 March. During this period, powering tests will verify the proper functioning of the LHC’s magnet circuits to the 7 TeV level (excluding the main dipoles and quadrupoles) before the start of the consolidation programme.