The past few weeks have been a record-breaking period for the LHC, with the machine now delivering long fills with unprecedented luminosity. Following the interruption in late May due to problems with the PS main power supply, on 1 June the operations team established collisions with 2040 bunches for the first time this year. This is the maximum number of bunches achievable with the current limitations from the SPS beam dump, which allows the injection of trains of 72 bunches spaced by 25 ns.
The following week saw LHC’s previous luminosity record at 6.5 TeV broken by a peak luminosity of just over 8 × 1033 cm–2 s–1, representing 80% of the design luminosity. This was followed by a new record for integrated luminosity in a single fill, with 370 pb–1 delivered in just 18 hours of colliding beams. The availability for collisions during this period was a remarkable 75%, more than double the annual average in 2015. Around 2 fb–1 were delivered during one week, breaking the previous record of 1.4 fb–1 established in June 2012.
These records follow the decision taken at the end of May to focus on delivering the highest possible integrated luminosity for the summer conferences. Following a short technical stop that ended on 9 June, the machine was re-validated from a machine-protection perspective for a sustained period of 2040 bunch operation at high luminosity. Afterwards, new records were set immediately, with one fill on 13–14 June producing more than 0.5 fb–1 in around 27 hours, and the following fill recording a peak luminosity of over 9 × 1033 cm–2 s–1. The record integrated luminosity delivered in seven days now stands at 2.4 fb–1. Finally, on 26 June, the team hit the LHC design luminosity (1034 cm–2 s–1) for the first time. With such performance, the operations team hopes to deliver over 10 fb–1 to both ATLAS and CMS before the summer conferences.
This is truly a new phase for the LHC and thanks are due to all the teams who have worked tirelessly to make it possible. This year the smaller beam size at the interaction points provides almost double the instantaneous luminosity compared to 2015, yet the machine is behaving impeccably. The stunning and surprising availability is due to a sustained effort over the years by hardware groups such as cryogenics, quench protection, power converters, RF, collimation, injection and others to maximise the reliability of their systems. Of particular note is the major effort co-ordinated by the radiation to electronics team to mitigate the effects of beam-induced radiation on tunnel electronics.
Another case in point concerns cryogenics. With so many bunches circulating, the heat load deposited by the electron cloud on the LHC beam screens in the arcs can reach 150 W per half-cell (a half-cell in an arc includes one quadrupole and three dipole magnets). This is just below the maximum of 160 W that can be sustained by the cryogenics system. With a new cryogenic feed-forward system in place to tune the beam-screen cooling parameters according to the intensity stored in the machine and the beam energy, operation with the high electron cloud currently present in the machine is significantly smoother than in 2015. Of course, the LHC remains a hugely complex machine and the availability is always liable to fluctuations.