LHC Report: Summer temperatures in the LHC
The LHC experiments have finished their data-taking period before the summer conferences. The machine has already delivered substantially more collisions to the experiments this year than in the whole of 2011. The LHC has now started a six-day Machine Development period, which will be followed by the second Technical Stop of the year.
The number of collisions delivered to the experiments is expressed in integrated luminosity. In 2011, the integrated luminosity delivered to both ATLAS and CMS was around 5.6 fb-1. On Monday 18 June, experiments finished taking data before the summer conferences and the integrated luminosity for 2012 so far is about 6.6 fb-1, well above the unofficial target of 5 fb-1.
The LHC’s performance over the last week of running was so efficient that the injection kicker magnets – which heat up due to the circulating beam – did not have time to cool down between the subsequent fills. As the time constants for warming up and cooling down are both of the order of many hours, the temperature of the injection kicker magnets is a good indicator of the LHC’s running efficiency. The all-time high record of luminosity production of over 1.3 fb-1 in a single week corresponds well with the highest measured kicker magnet temperature of 70°C. As these magnets lose their magnetic properties when the ferrites at their centre become too hot, a few hours of cool down time had to be included on a few occasions before the beam for the next fill could be injected. A programme is under way to reduce further the so-called “beam impedance” of the injection kicker magnets, which should substantially reduce this heating effect in the future.
On Monday evening, 19 June, the Machine Development period started during which accelerator physicists perform dedicated experiments to improve their understanding of the machine, thus paving the way for the future performance increase of the machine. On Monday 25 June, the second Technical Stop for machine maintenance will begin. The following weekend will be used to get the machine back to routine operation for physics from 2 July onwards.
by Jan Uythoven for the LHC Team
