LHC Report: Tests of new LHC running modes

On 13 September, the LHC collided lead ions with protons for the first time. This outstanding achievement was key preparation for the planned 2013 operation in this mode. Outside of two special physics runs, the LHC has continued productive proton-proton luminosity operation.

Celebrating proton-ion collisions.

The first week of September added another 1 fb^-1 of integrated luminosity to ATLAS’s and CMS’s proton-proton data set. It was a week of good and steady production mixed with the usual collection of minor equipment faults. The peak performance was slightly degraded at the start of the week but thanks to the work of the teams in the LHC injectors the beam brightness – and thus the LHC peak performance – were restored to previous levels by the weekend.

The LHC then switched to new running modes and spectacularly proved its potential as a multi-purpose machine. This is due in large part to the LHC equipment and controls, which have been designed with a great deal of flexibility. The machine’s repertoire was extended to colliding protons with lead ions and also “unsqueezing” proton beams at the collision points to 1000 m beta* for the experiments TOTEM and ALFA.

After Christmas the LHC will resume colliding protons with ions for the final period of physics data taking. Even though the LHC does not, in principle, change magnetically, proton-ion operation is a challenge for the RF system in the LHC and its synchronization with the SPS. The proton and ion beams are injected and ramped with different RF frequencies, and to collide these beams the frequencies have to be locked again, a process called re-phasing. Despite a 36 hour break to repair a vacuum leak that occurred at one of the LHC wire scanners (used to measure the transverse beam size), the first 4 TeV proton-lead collisions were recorded by the LHC experiments on 13 September - an outstanding achievement for all the teams involved.

Finally, after a short round of performance-related tests the LHC went back to its bread-and-butter of 4 TeV proton-proton physics, reaching the goal of 15 fb^-1 for ATLAS and CMS before the start of the five day Technical Stop #3 on the morning of Monday 17 September.

The theorists present their own interests in proton-ion collisions in the next article.

by Verena Kain for the LHC team