On 29 April, just after 8.00 p.m., the Large Hadron Collider (LHC) began circulating beams of protons for the first time this year. Extensive technical and maintenance work was undertaken since its end-of-year shutdown in early December, yet the restart of the 27 km-circumference superconducting collider has proceeded smoothly.
Magnet powering tests, which ensured the machine can be operated at an energy of 6.5 TeV per beam, were completed during the last week of April. This was followed by the machine-checkout phase, during which all equipment is placed in its operational state and the four LHC experiment caverns are patrolled and closed.
In the meantime, the crew of the Super Proton Synchrotron (SPS), which feeds protons to the LHC, worked hard to extract the single-bunch beam so that the LHC could be commissioned with beam. By the end of the afternoon on Friday 28 April, protons had been sent successfully down both transfer lines and were knocking at the LHC’s door. The following day, at 6.00 p.m., beam 1 (clockwise direction) was injected and threaded through the LHC’s eight sectors one at a time, circulating the entire machine after a period of 45 minutes. Beam 2 (anticlockwise direction) then went through the same process, and at 8.12 p.m. both beams were circulating. On Sunday 30 April, the single-bunch, low-intensity beams were successfully ramped to an energy of 6.5 TeV.
The next task, which was well under way as the Courier went to press, was to continue with detailed setting up of the machine while stepping up to higher bunch intensities and then multiple bunches. Each step in the intensity ramp up that follows has to be validated by circulating the beams from three fills for up to 20 hours, and the team is aiming for a configuration of 2550 bunches per beam, with each bunch containing of the order 1.2 × 1011 protons. Once stable beams have been declared, expected in the second half of May, the beams will be brought into collision and the second chapter of LHC Run 2 will be under way.