Accelerator Report: No summer holidays for the accelerator complex

Since the technical stop in June, Linac4 has been running quite smoothly, delivering beam to the PS Booster with good availability, of 98.7%. Despite a small water leak from the cooling system in one of the PS Booster quadrupole magnets, beam availability remains high, at 94%. The leak, though small, is being carefully managed by diverting the water outside the magnet to prevent further issues. Continuous monitoring is in place, using a camera and data from the water-cooling station. As long as the leak does not worsen, operations will proceed as usual until the end of the 2024 run. If the leak increases significantly, a spare magnet is ready for installation, which would require a beam stop of several days.

As mentioned in a previous Accelerator Report, physics at ISOLDE started on 8 April. Since then, approximately 20 different experimental runs have been conducted at the low-energy experimental stations, using various isotopes produced by impinging the high-intensity PS Booster proton beam on different types of targets. In parallel, the HIE-ISOLDE superconducting linear accelerator started the cooldown and conditioning of its 20 accelerating cavities mounted in four cryomodules and, last week, the first beams were accelerated to set up the experiments downstream. On 12 July, the physics campaign using post-accelerated isotope beams will start and continue until the end of the 2024 ISOLDE run, scheduled for 25 November.

On the SPS side, following the successful exchange of a magnet on 18 June, the SPS resumed beam delivery for its usual clients: the North Area and the LHC. However, on 25 June, the SPS operators received an alarm indicating that some magnets in the SPS were overheating. The magnets are equipped with a magnet protection system that prevents them from being powered when their temperature rises too high, which also stops beam production.

The experts discovered that a blockage in the water-cooling circuit was causing the overheating. The circuit was unblocked and refilled on 26 June, allowing beam production to resume. The blockage was caused by pieces of rubber that had remained in the circuit following an incident earlier this year.

Since resolving this latest and ­– hopefully – last issue, the SPS has had very good beam delivery, achieving beam availability of 97% for the LHC and 93% for the North Area, making up for some of the previously lost beam time. Additionally, the HiRadMat run, initially scheduled from 1 to 5 July, was already successfully completed by 2 July, allowing additional beam time for the North Area experiments.

The LHC resumed beam production on 28 June, after bringing forward some machine development (MD) activities to give the ATLAS experiment a chance to recover from a cryogenic cooling issue. Since then, the luminosity production has been good, although the beams have often been dumped prematurely due to various unrelated and mostly minor technical issues. Despite this, the LHC had a machine availability of 70% last week, with the time spent in colliding-beams mode (i.e. stable beam ratio) of 51.3%, slightly above our target of 50%.