LHC Report: here comes the summer!

Over the last three months the LHC has been gradually stepping up the total number of bunches in the beams and, early on Tuesday 28 June, the first fill with 1380 bunches per beam went into physics.


At present, the spacing between the bunches in the LHC is 50 ns, with some bigger gaps here and there to allow the injection and extraction kickers to do their job. The maximum number of bunches that we can inject in the machine with a 50 ns spacing is 1380, which is indeed the target for 2011. A nominal LHC bunch contains around 1.15x1011 protons. The 1380 nominal bunches now in use gives a total of 1.6x1014 protons per beam and a combined energy of around 89 MJ at 3.5 TeV. Happily the machine protection system is working very well.

After a rocky period, the start of last week saw some excellent machine availability and two back-to-back fills delivered 62 and 46 inverse picobarns. Both were dumped by the operations team, which is unusual because fills normally get taken out by one of a variety of problems – for example electrical network glitches caused by thunderstorms have been recent culprits.

Wednesday 29 June saw the start of an intense five-day machine development period. Many detailed studies were performed with the aim to push the performance of the LHC in both the short and the long term. Among the highlights were: the first injection of 25 ns bunch trains; the collision of bunches at 450 GeV with twice nominal intensity and smaller than nominal beam size; and another successful test of an optics designed for the future high luminosity LHC (HL-LHC).

This week, the LHC has been in a 5-day technical stop (4-8 July), which is to be followed by a sustained 6-week physics production run. The aim is to ramp quickly back up to 1380 bunches per beam and start “turning the handle”. The Booster and PS are able to offer somewhat higher bunch intensities and smaller beam sizes than those used at present, and the hope is to gently push these parameters in the search for even higher luminosities.


by Mike Lamont for the LHC Team