Installing high luminosity in the tunnel
The component concerned, known as a TANB, is the first definitive component of the High-Luminosity LHC to be installed in the Large Hadron Collider tunnel. An inauguration ceremony on Friday, 30 August, marked the arrival of this piece of equipment for the future collider.
The High-Luminosity LHC, which will be commissioned in 2026, will boost the performance of the current accelerator by substantially increasing the number of collisions in the experiments. Luminosity, which corresponds to the number of potential collisions per second per surface unit, is a crucial indicator of an accelerator’s performance. The higher the luminosity, the higher the probability of new discoveries.
Increasing the number of collisions, and therefore the number of particles in circulation, requires the protection of the LHC’s equipment to be reinforced, as particles that diverge from the trajectory can collide with sensitive components such as superconducting magnets and interfere with their operation. Protection is particularly important near the experiments. The billions of collisions occurring every second inside the detectors create the particles that are studied by the physicists. While almost all of these particles shoot off into the detector that surrounds the collision point, a miniscule number of them are emitted towards the tube where the beam circulates and can therefore reach the accelerator equipment.
The aim of the TANB absorber is thus to protect the accelerator equipment by stopping the particles near the LHCb experiment. During the current second long technical shutdown that will continue until 2021, the LHCb experiment will undergo major upgrades to enable it to record five times as many collisions from 2021 onwards. This collision rate will be kept at the same level for LHCb when the High-Luminosity LHC comes into service.
“Two of the same type of absorbers are already used on either side of the ATLAS and CMS experiments,” explains project leader Francisco Sanchez Galan. “However, we had to come up with a new design for LHCb, notably owing to a lack of space inside the accelerator.” Space is at a premium in the LHC, especially around the experiments. Therefore, it was necessary to design the simplest and most compact absorber possible.
Simplifying things can sometimes turn out to be very complicated. After a detailed design study and numerous simulations, engineers proved that it was possible to design an absorber that was more compact yet just as effective by positioning the equipment further away. Several models were proposed and the optimal absorber was finalised on paper before being manufactured in Germany. It measures only 65 centimetres in depth, as opposed to 5 metres for previous models.
An innovative positioning table was developed at the same time. “All its actuators are positioned on the side with easy access. We had to develop this model because the lack of space makes the adjustment of traditional tables on all four sides difficult, and in addition we needed to limit intervention time,” says Francisco.
Finally, the TANB’s integration was complicated by the lack of space. “Moving components and modifying the beam line allowed us to proceed millimetre by millimetre,” underlines Francisco. Mission accomplished, “thanks to the collaboration between numerous teams”, he smiles. Two TANB models have now been installed on both sides of LHCb, ready for the next collision run and high luminosity.