by David Silvermyr. Published: 22 July 2011

July started out with a few days of machine development for the LHC, followed by five days of scheduled technical stop; with the ALICE cavern frequently being accessed, up until 8 July, allowing work on improvements for many of ALICE’s subsystems1.

The LHC was almost ready for continued operation on the 10 July, when a thunderstorm, mid-morning, caused major electrical power disruption. The LHC lost power – notably to the cryogenics in most of its sectors – causing problems for many systems in both the LHC and ALICE. The shifters then on-duty at ALICE had to wait for over four hours before power was restored to the Alice Control Room and elsewhere.

This was a somewhat unpleasant waiting period, since we could not fully monitor the status of the detectors, down in the pit. Fortunately, all was well in the end - with no major issues - and ALICE was fully operational again by the next day, thanks to the hard work of many individuals, especially from the Detector Control System and Data Acquisition teams.

Following the recovery period from the power cut, the LHC delivered some startup fills, with an increasing number of bunches per fill: starting with 2, then 48, 264, 840, 1092, and finally 1380. The majority of these were of the new satellite-main configuration. Here, the main bunches from one beam collide, not with the main bunch of the other beam, but instead with a satellite bunch which is offset by 25 nanoseconds from the main bunch. This year the main bunches are separated by at least 50 nanoseconds.

The idea behind these satellite-main fills is to investigate whether this might allow ALICE to reach a reasonable luminosity while maintaining a low pile up of events for fills with a large number of bunches.

As of the 21 July, it is still a bit too early to say what the results of these initial tests and fills will be. The background conditions improved during the last fill with 1380 bunches, but unfortunately the target luminosity was not reached. It is possible that the satellite-main luminosity could improve in the future, but for now ALICE has returned to main-main collisions again.

Last but not least: in addition to the regular activities, there was also a special event at Point 2 on 20 July - the annual ALICE Week summer BBQ, which was organized by the ALICE CERN team and the secretariat - in particular Carnita Hervet.

  • 1. Including the Transition Radiation Detector, the Time Projection Chamber, the Time Of Flight, Silicon Pixel Detector, the Muon Chambers and the Electromagnetic Calorimeter.