With more luminosity delivered by the LHC between April and June 2012 than in the whole of 2011, the experiments had just what the collaborations wanted: as much data as possible before the summer conferences. By the time that a six-day period of machine development began on 18 June, the integrated luminosity for 2012 had reached about 6.6 fb–1, compared with around 5.6 fb–1 delivered in 2011.
The LHC’s performance over the preceding week had become so efficient that the injection kicker magnets – which heat up while beams continue to pass through them as they circulate – did not have time to cool down between fills. The kickers lose their magnetic properties when the ferrites at their centres become too hot, so on some occasions a few hours of cool-down time had to be included before beam for the next fill could be injected.
As the time constants for warming up and cooling down are both of the order of many hours, the temperature of the magnets turns out to provide a good indicator of the LHC’s running efficiency. The record for luminosity production of more than 1.3 fb–1 in a single week corresponds well with the highest measured kicker-magnet temperature of 70°C. A programme is now under way to reduce further the beam impedance of the injection kickers, which should substantially reduce the heating effect in future.
Routine operation of the LHC for physics is set to continue over the summer, with the machine operating with 1380 proton bunches in each beam – the maximum value for this year – and around 1.5 × 1011 protons a bunch. The higher beam energy of 4 TeV (compared with 3.5 TeV in 2011) and the higher number of collisions are expected to enhance the machine’s discovery potential considerably, opening new possibilities in the searches for new and heavier particles.
