The Large Hadron Collider (LHC) is awake. On Saturday, 29 April, just after 8 p.m., it began circulating beams of protons for the first time in 2017, two days earlier than originally foreseen.

On the road to putting the LHC back into operation, during the last week of April, the powering test period gradually gave way to the machine check-out. This is the phase where all equipment is operationally available and all the pieces of the puzzle fall into place to complete the image.

One of the main steps of the machine check-out is the closure of the Beam Interlock System (BIS) loop, which requires all equipment to be in the operational state and the four experimental caverns to be patrolled and closed. Actually, everything must be set up as if the machine would be ready to receive beam. On Friday, 28 April, the machine and all its power converters were tested – cycled – from injection to acceleration, all the way to the flat-top and the squeeze phase, as if there was beam in the machine. After a few attempts and the resolution of some pending issues, the loop could finally be closed during the night of Friday, 28 to Saturday, 29 April, just before the long weekend. Many checks were made in parallel on all other systems required for beam operation.

In the meantime, the SPS crew worked hard to get the extraction of the single bunch beam from long straight sections 4 and 6 working for the commissioning with beam of the LHC. Initially the beam was sent successfully to the beam dumps close to the SPS, before going down through the TI2 and TI8 transfer lines to the LHC. By the end of the afternoon on Friday, the beam had been successfully sent down both transfer lines, knocking at the LHC’s door.

The first LHC beam injection was foreseen for Monday, 1 May. Given the impressive advancement that had been made prior to the long weekend, a first attempt was made to get everything ready on the morning of Saturday, 29 April to inject the beam. Unfortunately, a few issues were discovered at the last minute that delayed the injection. Thanks to the dedication of equipment specialists who worked over the long weekend, the issues were successfully solved in one day.

At 6 p.m., the first injection of beam 1 (clockwise direction) was started. The beam was then brought around the machine step-wise, going one sector further each time. Just 45 minutes later, the beam went all the way round and was circulating. Beam 2 (anti-clockwise direction) then went through the same process, and at 8.12 p.m., both beams were circulating, two days ahead of schedule.

Then, on the afternoon of Sunday, 30 April, the circulating single-bunch low-intensity beams were successfully accelerated up to 6.5 TeV per beam.

This remarkable achievement was made possible thanks to the good preparation of the machine and all its sub-systems by the equipment experts and the dedication of several experts in close collaboration with the operations teams in the CCC over the long holiday weekend.

Now the work continues with the detailed setting-up of the machine, initially with low-intensity single bunches and later with higher-intensity and then multiple bunches, to validate each step in the process, after which collisions can be made safely and physics can start in a few weeks’ time.