Following upgrade round two for CERN's Large Hadron Collider (LHC), the schedule for a third round that will allow unprecedented data collection is uncertain.
The LHC is the world’s largest particle collider, which has been closed for a three-year upgrade known as Long Shutdown 2. This second and latest upgrade equips the LHC with better protected magnets and more sensitive detectors, among other improvements.
The machine will start running experiments again in February 2022 if all goes well with the two-week test run in October, said Prof Joachim Mnich, a physicist and the director for research and computing at CERN who sits on the organisation’s Scientific Policy Committee, which had its latest meeting this week to set research priorities and evaluate past progress.
The Committee discussed plans for the LHC’s third upgrade, which will allow it to withstand higher luminosity – the amount of light produced by particle collisions. The more collisions there are, the more data there is, the greater the luminosity.
CERN plans to begin the third upgrade in 2025 after a three-year testing phase. The upgrade will allow the collider to withstand 10 times more collisions per second, producing more – and more accurate – data for analysis. The upgraded LHC’s higher sensitivity will allow it to detect particle characteristics and behaviours that the current version cannot.
However, remaining technical challenges in its construction, as well as disruptions caused by the pandemic, have raised questions about whether construction will stay on schedule, Mnich said.
Technical challenges include the development of high field magnets. “These magnets needed to squeeze the proton beam in order to reach the higher collision rate (luminosity) must have a magnetic field (11 Tesla) higher than the magnets now in use in the LHC (8.3 Tesla),” he explained.
The tesla is a unit that measures the strength of a magnetic field. In order to create these field magnets, researchers will need to develop cables made of new superconducting material.
CERN will also need to upgrade the detectors that analyse colliding particles. They will need to be equipped with radiation hard sensors and electronics to be able to process higher luminosity, he said.
Over the next few months, CERN will bring in external, international experts to assess the upgrade challenges and the progress being made. The experts will then advise CERN management on whether they need to revise the schedule.
The pandemic has slowed work on many lab-based projects. Labs were closed for a period last spring, effectively bringing all lab work to a halt, said Mnich. Between last summer and this June, there was a limited re-opening, allowing the bare minimum number of local and visiting researchers to return.
Since June, restrictions have eased and the norm is now to work on campus, with appropriate social distancing measures in place, Mnich said. CERN got the particle accelerators – which can feed into the LHC – up and running this summer, allowing smaller experiments to progress.
It has been important to get visiting researchers back on campus, because many experiments at CERN rely on hands-on, international expertise, he explained. Bringing in visiting researchers will be all the more important for resuming LHC experiments in February, he said.