Autopsy of an LHC Beam Dump

Summary

For the first time at CERN, an autopsy has been carried out on a radioactive beam dump. Inspection of the inner workings of the device helped the teams to find out more about how materials behave under the impact of high-energy beams During LS2, the LHC’s two external beam dumps were removed from the tunnel and replaced with spare ones. After ten years of operation, they were showing signs of degradation, notably nitrogen leaks. Before being installed, the spare dumps were modified and upgraded to prevent the same problems from occurring during Run 3 (see this Bulletin article published in 2020). To find out more about the cause of the nitrogen leaks, an endoscopy was carried out in July 2020. It revealed unexpected cracks in the beam dump’s two extruded graphite discs (see box). An action plan was drawn up by the SY-STI (Sources, Targets and Interactions) group as more information was needed with Run 3 on the horizon, especially with a view to designing new spare beam dumps for the LHC and, beyond that, beam dumps for the HL-LHC. To access the dump’s three main components – high-density, low-density and extruded graphite (see below) – there was only one possible solution: perform an “autopsy” on one of the dumps. Given its radioactivity levels, this was easier said than done. “To reach the heart of the beam dump, we needed to be able to open it…,” says project leader Ana-Paula Bernardes. “But its duplex-stainless-steel-alloy housing was extremely difficult to cut. The first attempt, in January 2021, under a framework contract, was unsuccessful: it was impossible to cut through it manually without exceeding the radiation dose limits. We considered outsourcing the job to a specialised external company with the right equipment for the task, but the costs and time frames were incompatible with the project.” Top: Longitudinal test cut with the circular saw, performed by the SY-STI group. Solution chosen for the cutting of the radioactive dump. Middle: Positioning of the...