LHC Report: Ramp-up complete

The intensity ramp-up outlined in the last Bulletin continued more or less as planned, with some steady running with 1092 bunches followed by the final step-up to 1380 – the maximum number of bunches for the year.

Monday, 16 April was spent performing luminosity calibration. Under carefully controlled conditions and a special beam configuration, the experiments' luminosity measurements were calibrated against a measurement of the accelerator’s absolute luminosity obtained with Van der Meer scans. These scans give the beam sizes at the interaction point which, together with an accurate measurement of the beam and bunch currents (and other more subtle considerations), allow a precise measurement of the absolute luminosity.

With the Van der Meer scans out of the way, the final step-up in the number of bunches to 1380 was made. This has resulted in an average peak luminosity of around 5.6x10³³ cm^-2s^-1 in the general-purpose detectors (ATLAS and CMS have yet to publish their calibrated values). The performance of the machine at this early stage of the year is encouraging: during the ramp-up over half an inverse femtobarn was delivered in a week and the total for the 2012 run is now touching one inverse femtobarn.

The LHC comes out of the technical stop this Friday evening and, after re-qualification and a fast ramp back to 1380 bunches, the plan is for some steady physics running.

by Mike Lamont for the LHC Team