LHC Report: Positive ion run!

The current LHC ion run has been progressing very well. The first fill with 358 bunches per beam - the maximum number for the year - was on Tuesday, 15 November and was followed by an extended period of steady running. The quality of the beam delivered by the heavy-ion injector chain has been excellent, and this is reflected in both the peak and the integrated luminosity.


The peak luminosity in ATLAS reached 5x1026 cm-2s-1, which is a factor of ~16 more than last year's peak of 3x1025 cm-2s-1. The integrated luminosity in each of ALICE, ATLAS and CMS is now around 100 inverse microbarn, already comfortably over the nominal target for the run. The polarity of the ALICE spectrometer and solenoid magnets was reversed on Monday, 28 November with the aim of delivering another sizeable amount of luminosity in this configuration.

On the whole, the LHC has been behaving very well recently, ensuring good machine availability. On Monday evening, however, a faulty level sensor in the cooling towers at Point 4 caused the loss of primary cooling water for a short time. This disturbed the operation of the cryogenics system, and one knock-on effect was the warming of a 500m superconducting link between a feed-box and magnets situated near to Point 3. The cryogenics recovery and the cool-down of the link took until Wednesday afternoon. The warm-up of the link required some revalidation tests of the magnet circuits, and beam was finally back early Thursday morning.

In the following days, there will be a luminosity calibration exercise using Van der Meer scans. There will also be some machine studies related to future performance improvements. Otherwise, the accelerator teams are looking forward to the end of the run on Wednesday, 7 December.

by Mike Lamont for the LHC Team