New beam absorber
An internal beam absorber stops stray particles in order to prevent them from harming the accelerator. The new target dump injection segmented (TDIS) absorber is made up of three modules, each measuring 1.6 metres, and replaces equipment made of a single element measuring a little over four metres.
The modules comprise two jaws similar to those of a collimator, made of increasingly dense materials, namely graphite, titanium and copper, along the entire length of the absorber, which slow down and then stop the beam. One advantage of this beam absorber is its smaller size, thanks to its optimised design.
Preparing for HL-LHC: the neutral beam absorber
Two new neutral beam absorbers (TANB) were installed on both sides of the LHCb experiment to protect the accelerator equipment. Increasing the number of collisions, and therefore the number of particles in circulation, requires reinforced protection of the LHC’s equipment, as particles that diverge from the trajectory can collide with sensitive components such as superconducting magnets and interfere with their operation.
Increased cryogenic power at LHC Point 4
The LHC cooling system is made up of cryogenic islands with eight helium refrigerators in total. Each even-numbered point on the accelerator (Points 2*, 4, 6 and 8) has two refrigerators, one dating from the LEP (Large Electron–Positron Collider) era, and another, newer, refrigerator dating from the start-up of the LHC. The LEP refrigerator is composed of two cold boxes – one on the surface and the other downstream in the tunnel, which cool the helium from room temperature to 20 K (-253.15 °C) and from 20 K to 4.5 K respectively – and a unit located in a cavern generating superfluid helium at 1.9 K.
The Point 4 refrigerators are crucial for the HL-LHC because, as well as cooling Sectors 3–4 and 4–5, they must also cool the sections where the radiofrequency cavities are installed, which require a considerable amount of cooling.
To achieve this important extra 2 kW, the four turbines and heat exchangers in each of the cold boxes at Point 4 have been replaced with higher-performing equivalents. This task was relatively straightforward to carry out for the cold box at the surface, which is easily accessible to workers, but more arduous for the cold box in the tunnel.
