LHC report: Ticking over

The past two weeks have seen luminosity production rates vary somewhat but the overall upwards slope has remained steady. Over 17 fb-1 have been delivered to both ATLAS and CMS; LHCb is also doing well, with around 1.6 fb-1 delivered so far in 2012. The proton physics production also slotted in a five-day machine development period (8-13 October). When producing the LHC beam in the PS, some parasitic low-intensity satellite bunches are formed 25 ns from the main bunches, which are spaced by 50 ns. ALICE, whose detector is designed to work with relatively low collision rates, has been taking data from satellite-main collisions. The population of these satellites has recently been increased thanks to gentle tweaks by the PS radio frequency experts. This has increased the peak luminosity in ALICE and will help them to reach their proton-proton integrated luminosity goal for the year.

The October machine development programme was a mixed bag. While some studies were aimed at short-term operational improvements, others concentrated on necessary developments for post-long-shutdown running with 25 ns beam. In the latter category there were: further systematic investigations of beam instabilities; a successful attempt to squeeze to a beta* of 40 cm; and tests by the RF team of a technique to handle the increased power requirements of the 25 ns beam. The weekend following the machine development was dogged by a number of technical issues and was consequently not very productive from a luminosity perspective. In contrast, Saturday 6 October, just before the machine development period, saw a new record of 286 pb-1 delivered in one day.

Because of the tight vacuum limits imposed by the injection team in and around the newly installed injection kicker magnet, the 2012 scrubbing run has been pushed to the end of the year's proton run. The scrubbing run will include the injection of a large number of 25 ns spaced bunches. This will inevitably generate high vacuum levels. As such, the injection team prefers that the risks for the kicker magnet associated with relaxing their limits and operating with these higher levels only be taken when the proton run is effectively over.