LHC Report: Rocky XIV

The LHC has been in luminosity production mode for the last couple of weeks. Peak luminosities have ranged between 6 and a record 7.74 x 1033 cm-2s-1. Integrated luminosities per fill have been healthy, with 170 inverse picobarn per fill reached on five occasions in the last two weeks. The total integrated luminosity for the year has passed 14 inverse femtobarns.

Injected bunch currents have peaked at an average of  1.69 x 1011 protons per bunch on average – a remarkable achievement for both the injectors and the LHC: the injectors to be able to produce good quality beam at these intensities; the LHC for being able to cope with these intensities without excessive losses. Peak performance from day to day depends strongly on the beam sizes and bunch intensities delivered by the injectors. It is a continual challenge to keep the Booster, PS and SPS optimally tuned while they deliver beams to their other wide range of users.

Despite the excellent peak performance and wrestling with the usual vagaries of a 27-kilometre superconducting collider, LHC Operations has been hit by a number of longer time-outs. The most serious of these was a problem with one of the mirror assemblies of the synchrotron light telescope system or BSRT (Beam Synchrotron Radiation Telescope). The BSRT collects photons emitted by the protons as they are bent in the field of a specific magnet to produce a transverse image of the beam. The beam size extracted from analysis of the image provides a very important diagnostic.

The photons are initially reflected into the telescope system by a mirror situated near the beam. It is possible that an accelerator component can act like an accidental antenna and pick-up the electromagnetic fields from the intense proton beams thereby inducing localized heating. This appears to have happened  to one of the BSRT mirror assemblies. Investigations showed that the mirror assembly had been deformed by over-heating, necessitating an opening of the vacuum for extraction of the mirror and supporting device. The whole exercise took around two days. The Beam Instrumentation group is preparing a more robust design for installation during the next technical stop.

This week sees this year's first look at proton-ion operation. This in preparation for the proton-ion run in January 2013. The first proton-lead collisions are planned for Wednesday 12 September.