LHC Report: the machine - on the level

The LHC has held the number of bunches per beam at 1092 over the last couple of weeks and has been delivering luminosity to the experiments at a healthy rate. The integrated luminosity total has already passed 1 inverse femtobarn (fb^-1), which was the overall goal for the year. There was a modest celebration in the CCC to mark the occasion. Modest celebrations are now on hold until the end of this year's run or the delivery of 5 fb^-1.

LHCb is designed to perform different types of physics searches from those at ATLAS and CMS, and is limited to a peak luminosity of about 3x10³² cm^-2s^-1. If the beams were to be collided head-on in the LHCb detector, this figure would be exceeded. Therefore the beams are initially separated by a few microns in the vertical plane and then, as the beam intensity decays during a fill, this separation is gently reduced to keep the luminosity constant at the acceptable maximum. This technique is known as 'luminosity levelling' and has been used successfully to deliver around 0.36 fb^-1 to LHCb in 2011, well on the way to their target of 1 fb^-1 for the year.  

As expected, high beam intensities have introduced a number of issues including: UFOs, the effect of radiation on the electronics installed in the LHC tunnel; and beam-induced heating of some accelerator components. Understanding, and where possible mitigating, these effects is ongoing, hence the more sedate pace in pushing the beam intensity recently. The operations team has successfully pushed up the number of bunches per beam to 1236 and they hope to make the step up to 1380, the final target of 2011, before the start of next machine development (MD) period, on 29 June. The MD sessions will be followed by a 5-day technical stop, which will take us to 8 July when operation for physics will start again.

by Mike Lamont for the LHC Team