LHC Report: Rocky re-start

A rocky re-start with beam followed a successful machine development period and the first technical stop of 2012. Today, Friday 11 May, the machine began running again with 1380 bunches.


A short, two-day machine development period was successfully completed on 21-22 April. It focused on topics relevant for the 2012 physics beam operation. This was then followed by a five-day technical stop, the first of the year. The technical stop finished on time on Friday 26 April.

The re-start with beam was somewhat tortuous and hampered by an unlucky succession of technical faults leading to extended periods of downtime. The planned intensity increase was put on hold for three days with the machine operating with 1092 bunches and a moderate bunch intensity of 1.3x1011 protons. This delivered a reasonable peak luminosity of 3.6x1033 cm-2s-1 to ATLAS and CMS. Higher than usual beam losses were observed in the ramp and squeeze, and time was required to investigate the causes and to implement mitigation measures.

As of 9 May, integrated luminosities of 1.2 fb-1 were delivered to ATLAS and CMS, 0.11 fb-1 to LHCb, and 0.32 pb-1 to Alice. Ahead is a running period for physics with the aim to quickly reach and exceed pre-technical stop peak luminosities and deliver a sizable amount of data in time for the summer conferences.

by Barbara Holzer for the LHC Team