LHC Report: Freshly squeezed beams!

After careful validation of  new machine settings, the LHC was ready for higher luminosity operation. New luminosity records have been set, but the operations team continues to wrestle with machine availability issues.


The commissioning of the squeeze to a ß* of 1 m in ATLAS and CMS described in the last Bulletin took until Wednesday, 7 September to complete. In order to validate the new set-up, beam losses were provoked in a controlled way with low intensity beams. The distribution of beam loss around the machine in these tests is known as a loss map. The loss maps showed that the collimation system is catching the large majority of beam losses as it should, and that the machine was ready for us to ramp the number of bunches back up and go to physics production.

The ramp-up of the number of bunches went smoothly with fills at 264, 480, and 912 bunches on the way back to the machine’s previous record of 1380 bunches (first fill on Friday, 9 September). The 1 m ß* squeeze paid off of with the expected 50% increase in luminosity. After gently increasing the bunch intensity, the peak luminosity was up to a truly impressive 3.3x1033 cm-2s-1. This is one third of the design luminosity - delivered at half design energy, with half the design number of bunches, and without the full squeeze (the design ß* at full energy is 0.55 m). This is possible due to the excellent beam quality produced by the injectors, which provide the LHC with bunches with small transverse beam sizes and a higher-than-nominal number of protons per bunch.

Integrated luminosity potential was also demonstrated, with one fill delivering 115 inverse picobarns to Atlas and CMS in around 17 hours. However, the LHC is still a big beast running with high intensity beams and the operations team continues to wrestle with machine availability issues. The total integrated luminosity for the year is now around 3.4 inverse femtobarn in Atlas and CMS and 0.88 inverse femtobarn in LHCb with 5 weeks of proton physics operation left in 2011.


by Mike Lamont for the LHC Team