2016 was a remarkably successful year for CERN’s Large Hadron Collider (LHC), marked by excellent peak performance, good availability and operational flexibility (CERN Courier December 2016 p5). Targeting further improvement, a thorough review of LHC operation and system performance was the focus of discussions in the first phase of the annual LHC performance workshop, which took place from 23 to 26 January in Chamonix, France.
Experts from the accelerator sector, CERN management and members of the CERN Machine Advisory Committee explored the operational scenarios for the remainder of Run 2 and made preliminary decisions regarding optics and machine parameters. Beam is due back in the LHC this year at the beginning of May, and the rest of the year will essentially be dedicated to proton–proton physics, with the usual mix of machine development and special physics runs. By quantifying the limitations to peak luminosity from electron-cloud effects, the cryogenics system and other factors, luminosity estimates for the coming years were also drawn up: in 2017, the peak luminosity should be at least 1.7 × 1034 cm–2 s–1 and the integrated luminosity target for ATLAS and CMS is 45 fb–1.
One open question about future LHC operations concerns the increase of the beam energy from 6.5 to 7 TeV per beam, which would see the machine reach its design specification. To gain input on high-field magnet behaviour, a dipole training campaign was conducted at the start of the year-end technical stop (CERN Courier March 2017 p9). Experience from this and previous training campaigns was reviewed and the duration, timing and associated risks of pushing up to 7 TeV – including implications for other accelerator systems, such as the LHC beam dump – were explored. There will be no change of beam energy in 2017 and 2018. The goal is to prepare the LHC to run at 14 TeV during Run 3 with the experiments expressing a clear preference to make the change in energy in a single step.
Regarding the longer-term future of the LHC, the High-Luminosity LHC (HL-LHC) demands challenging proton and ion beam parameters from the injector complex. The LHC injector upgrade (LIU) project is charged with planning and executing wide-ranging upgrades to the complex to meet these requirements. Both the LIU and HL-LHC projects have come through a recent cost-and-schedule review, and at present are fully funded and on schedule. The injector upgrades will be deployed during Long Shutdown 2 (LS2) in 2019/2020, while the HL-LHC will see the major part of its upgrades implemented in LS3, which is due to start in 2024.
With only two more years of operation before the next long shutdown, planning for LS2 is already well advanced. For the LHC itself, LS2 will not require the same level of intervention as seen in LS1. Nonetheless, here is still a major amount of work planned across the complex including major upgrades to the injectors in the framework of LIU, and significant upgrades to the LHC experiments.
The exploitation of the LHC and the injector complex has been impressive recently, but work across the Organization continues unabated in the push to get the best out of the LHC in both the medium and long term.