(Video: Noemí Carabán/CERN)
Beams do not circulate inside accelerators forever. As particles collide with the sides of the beam pipe or with each other, the beams "degrade" – they become less likely to give collisions that could lead to interesting physics.
Accelerator physicists can then choose to "dump" the beams, removing them from the accelerator and sending them to be safely absorbed at a "beam dump" – usually by a radiation-shielded block deep underground.
In the video above, CERN engineers install a new beam dump on the Proton Synchrotron Booster – a key element in the CERN accelerator complex that has been delivering protons to the Proton Synchrotron (PS) since 1972.
The Booster is made up of four superimposed synchrotron rings that receive beams of protons from linear accelerator 2 (Linac 2) at 50 MeV and accelerate them to 1.4 GeV for injection into the PS. Before the Booster received its first beams on 26 May 1972, protons were injected directly from Linac 2 into the PS, where they were accelerated to 26 GeV. The low injection energy of 50 MeV limited the number of protons the PS could accept. The Booster allows the PS to accept over 100 times more protons, which greatly enhances the beam's use for experiments.
The original beam dump on the PS Booster was designed in the 1960s to cope with beam energies in the order of 800 MeV from Linac 2. But after the second long shutdown of CERN accelerator complex in 2017-2018, the higher energy Linac 4 is scheduled to replace Linac 2 as the source of protons for the Large Hadron Collider. So the new PS Booster dump is expected to withstand beams of up to 2 GeV.
"The new beam dump is cylindrical like the old one, but it is larger in length and diameter, so it will stop more particles," says CERN engineer Alba Sarrió, who led the project to replace the dump. "The new dump is an alloy of 99% copper, with traces of chromium and zirconium. This gives it favourable thermo-mechanical properties compared to the old, iron beam dump." Sarrió says the new beam dump should last for 25-30 years.
This video shows the installation of that new dump core inside a cavity one metre in diameter, surrounded by five shielding rings made of concrete and steel. The replacement is the culmination of months of preparation, an interdisciplinary work involving several teams from the Engineering, Beams and Technology departments, as well as the collaboration and supervision of radioprotection experts.