Last Tuesday 25 October, saw the last beams of the LHC’s 2016 proton run, and what a run it has been. At the beginning of the year, we set ourselves the target of reaching the machine’s peak design luminosity of 1034 cm–2s–1, by the end of the run we were regularly operating at 30 % above that. Our target for the integrated luminosity for 2016 was 25 inverse femtobarns. We reached 40.
This success is underscored by the most amazing statistic of the year: in 2016, the LHC spent 60% of its operational time delivering stable beams to the experiments. I can’t overstate the significance of this, because the total number of collisions we deliver to the experiments – the integrated luminosity - determines the capacity they have to carry out the great research that they do. The higher the availability of the machine, the more data we can deliver. It’s as simple as that.
To put this in context, the LHC availability target we set for 2016 was an ambitious 50%. You might say we were not being ambitious enough, but this is a figure based on decades of experience. The Large Electron Positron collider, LEP, for example concluded its very successful research career with 30% availability, and LEP was a much simpler machine. The fact that we can run the LHC with such reliability is a resounding testimony to the quality of the machine, those who designed it and those who run it. It is also a very good sign for the machine’s high-luminosity future.
The 2016 run was not without issues, however, and although it seems like a distant memory now, just a short while ago we were struggling through the dark month of May, dealing with issues ranging from the now-infamous beech marten with a penchant for high voltage to problems with the vacuum in the SPS beam dump and with the PS main power converter system. It’s good not to forget these. They serve to remind us that with such a complex machine as the LHC, we can never be complacent.
The fantastic 2016 statistics belie the fact that the run was limited by some of these issues. SPS vacuum problems meant we could only inject 2200 bunches instead of the 2700 planned. And de-gassing in an LHC injection kicker, a magnet that steers bunches of particles into the LHC, limited the number of particles in each bunch.
The conclusion of the proton run is not, of course, the end of the LHC’s 2016 run. We’re now moving into a few weeks of collisions between lead-ions and protons, which will be carried out at collision energies of 5.02 and 8.16 TeV. This is the first time we’ve done lead-proton collisions since 2013, providing data important for interpreting the results of the lead-lead collisions. It’s also the last ion run until 2018, since we have a longer than usual end of year technical stop this year to address issues such as the SPS beam dump vacuum leak.
Finally, we’ll conclude the LHC’s 2016 campaign with some preparations for the future. We have invested one week of proton physics running in order to have two full weeks instead of just one to start re-training sectors 3-4 and 4-5 to get more information for LHC running at the design energy of 14 TeV. News from this work will provide valuable input to the 2017 LHC performance workshop in January, which will set the scene for the coming years at the energy frontier.
Frédérick Bordry is CERN Director for Accelerators and Technology