A few months ago, the ATLAS Collaboration presented its schedule for the second long shutdown 2 (LS2) concerning the detector’s repair, consolidation and upgrade activities. Since then, the experiment’s LS2 programme has been refined to best meet needs and constraints.

Although ATLAS was originally supposed to install two new muon detectors in the forward regions (new small wheels) – measuring 9.3 metres in diameter and developed to trigger and measure muons precisely despite the increased rate of collisions expected at the High-Luminosity LHC (HL-LHC) – only one will be installed during LS2. “While considerable progress has been made on the assembly, the second wheel will not be ready before the end of LS2. So we decided to aim for installing that one in the next year-end technical stop (YETS, at the end of 2021),” says Ludovico Pontecorvo, ATLAS Technical Coordinator. A replacement of the first small wheel (on side A of the detector) is foreseen for August 2020.

Another major component of the Phase-1 upgrade for ATLAS is the improvement of the trigger selection for the operation at the future HL-LHC, which requires new electronics to achieve a higher resolution of the electromagnetic calorimeter’s trigger. It also involves upgrading the level-1 trigger processors, and installing new electronic cards for the trigger and data-acquisition (TDAQ) system. “The installation of new electronics for the liquid-argon calorimeter is proceeding smoothly and we are advancing through the different stages of production for the TDAQ deliverables. The upgrade of the infrastructure and the necessary maintenance work is almost completed. The first phase of our HL-LHC upgrade programme has started,” says Ludovico Pontecorvo.

In parallel, the consolidation of the detector system is progressing according to schedule. “We have replaced cooling connectors connecting the modules of the tile calorimeter to the overall cooling infrastructure in almost all 256 modules of the calorimeter and the standard maintenance of the read-out electronics is ongoing. In addition, the scintillators located between the central barrel and the extended barrels of the tile calorimeter are currently being installed,” adds Ludovico Pontecorvo. 

ATLAS teams are also preparing for the following long shutdown (LS3, starting in 2024), which will see the installation of an all-new inner tracker. Located at the centre of the ATLAS detector, the role of the inner tracker is to measure the direction, momentum and charge of electrically charged particles produced in each proton–proton collision. During LS3, an all-silicon inner tracker will replace the current one, using state-of-the-art silicon technologies to keep pace with the HL-LHC rate of collisions. The manoeuvre to lower and insert this new element (2 m in diameter, 7 m long) looks arduous, so, in March, the team in charge of its installation took advantage of the shutdown to practice the procedure in the cavern with a mock-up of the tracker. The two lowering options tested required a great meticulousness, given that, at the worst moment, the margin was only a few centimetres.

* Don’t miss the ATLAS new muon small wheel at Building 191 during the CERN Open Days on 14 and 15 September!

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