The last couple of weeks of operation have been a mixed bag, with time dedicated to TOTEM and ALFA; a floating machine-development period and luminosity calibration runs. These special running periods were interleaved with some standard proton running where we’ve struggled a little to recover previous highs. The LHC has now returned to more routine operation.
The TOTEM and ALFA run required the development of special optics to produce large beam sizes and smaller angular spread at the interaction points in ATLAS and CMS. These special optics produce shallower angled proton-proton collisions than normal and allow experiments to probe the tiny angle-scattering regime. The qualification of the new set-up at 4 TeV went well, paving the way for a 13-hour physics run for both TOTEM and ALFA with their Roman pots in position.
Highlights from the 48-hour machine development period included the injection of high intensity bunches using new SPS optics. A low number of bunches with 3 × 1011 protons per bunch was injected, ramped, squeezed and collided in attempts to provide exceptionally high pile-up to ATLAS and CMS – peaks of around 70 collisions per bunch crossing were achieved. There was also further development of the candidate optics for the high luminosity LHC, which achieved a record squeeze factor at the interaction points.
The LHC's 2012 proton physics run has been extended until 17 December, with the 4-week proton-ion run pushed into January to February 2013. This will give two sustained periods of proton-proton running split by machine development and a technical stop in September. The aim here is to maximize the delivered integrated luminosity before the start of the long shutdown (LS1), which will now start mid-February. The length of LS1 remains the same with beam foreseen to be back in the LHC towards the end of 2014.