LHC Report: a record start for LHC ion operation

After the technical stop, the LHC switched over to ion operation, colliding lead-ions on lead-ions. The recovery from the technical stop was very smooth, and records for ion luminosity were set during the first days of ion operation.

The LHC technical stop ended on the evening of Friday, 11 November. The recovery from the technical stop was extremely smooth, and already that same evening ion beams were circulating in the LHC. ‘Stable beams’ were declared the same night, with 2 x 2 bunches of ions circulating in the LHC, allowing the experiments to have their first look at ion collisions this year.

However, the next step-up in intensity – colliding 170 x 170 bunches – was postponed due to a vacuum problem in the PS accelerator, so the collisions on Sunday, 13 November were confined to 9 x 9 bunches. The vacuum problem was solved, and on the night of Monday, 14 November, trains of 24 lead bunches were injected into the LHC and 170 x 170 bunches were brought into collision through the accumulation of several injections.

The resulting peak luminosity at the experiments, of 1.5x10²⁶ cm^-2s^-1, was already 5 times last year’s record. This successful result was due to the smaller beam size at the collision points in the experiments, the so-called ß*, which was also partly responsible for the success story for proton operation this year. Other contributing factors are the larger number of bunches (only up to 137 bunches in 2010) and the extremely good beam quality from the injector chain.

The next fill on Tuesday evening (15 November) beat this record luminosity by more than a factor of two by increasing the number of bunches to 358 x 358. This record fill gave a peak luminosity of 3.5x10²⁶ cm^-2s^-1 and collected an integrated luminosity of more than 40 % of the whole 2010 ion run in about 6 hours of physics. This is extremely promising for the ion physics run ahead, which will continue until 7 December.

by Jan Uythoven for the LHC Team