Earlier this month, protons collided in the Large Hadron Collider (LHC) at the record-breaking energy of 13 teraelectronvolts (TeV) for the first time. These test collisions were to set up systems that protect the machine and detectors from particles that stray from the edges of the beam. ALICE captured these collisions one of which can be seen in the image below:
A key part of the process was the set-up of the collimators. These devices which absorb stray particles were adjusted in colliding-beam conditions. This set-up will give the accelerator team the data they need to ensure that the LHC magnets and detectors are fully protected.The LHC Operations team continues monitoring beam quality and optimisation of the set-up.
Last month proton beams were back in the accelerator for the first time after two years of intense maintenance and consolidation. The first beam at the record energy of 6.5 TeV circulated on 10 April, and the first collisions – at the lower beam energy of 450 gigaelectronvolts (GeV) – followed. This gave the opportunity to the operations team to check and fine-tune all the beam instruments, magnets and collimators along the 27-kilometre accelerator.
"When we start to bring the beams into collision at a new energy, they often miss each other," says Jorg Wenninger of the LHC Operations team. So we have to scan around – adjusting the orbit of each beam until collision rates provided by the experiments tell us that they are colliding properly." The design of the LHC allows more than 2800 bunches of protons to circulate in each beam at a time. But the LHC Operations team will start collision tests with just one or two bunches per beam at the nominal intensity of 1011particles per bunch to ensure that all is running smoothly.
This is an important part of the process that will allow the experimental teams running the detectors ALICE, ATLAS,CMS, LHCb, LHCf, MOEDAL and TOTEM to switch on their experiments fully. It is one of the many steps required to prepare the machine before the LHC's second physics run can begin. The LHC Operations team plans to declare "stable beams" in the coming weeks – the signal for the LHC experiments to start taking physics data at this new energy frontier.
Data taking and the start of the LHC's second run is planned for early June.