Assembly of Big Wheels sectors in building 180

After completing the preparation of the sectors of the wheels TGC-1 (first layer of trigger chambers) and MDT (precision chambers) for the side C of ATLAS last spring, the work in building 180 has advanced quickly during the summer: all the sectors for TGC-2-C have been completed during the month of August; currently, two sectors for TGC-3-C are complete, and work is underway for three others. Similarly, assembly, integration and commissioning have progressed well also with the precision chambers, with 12 of the 16 sectors for MDT-A being complete now, and the end of this significant phase of work is only a few weeks ahead of us.

Sectors for the TGC-2 wheels on the C-side. (Image: ATLAS Experiment/CERN)
MDT chambers on the A-side stored in building 180. (Image: ATLAS Experiment/CERN)
Sectors of the first big wheel (TGC Trigger chambers) mounted of the end-wall of the ATLAS cavern. (Image: ATLAS Experiment/CERN)

Installation of the first Big Wheel

The sectors of the TGC-C-1 wheel, the first layer of trigger chambers, have been mounted on one end-wall of the ATLAS cavern. With all the sectors mounted to form a wheel, the end-cap muon spectrometer starts to show its full size and complexity. After the installation of the sectors, which has been accomplished very smoothly, the coming weeks will see the completion of the installation of services and the mechanical connections to the rails, in preparation of the movement close to the final position, against the barrel toroid and the muon barrel.

The inner layer of the end-cap spectrometer includes on each side eight stations formed by one MDT and two or three TGC chambers, positioned downstream of the inner layer of the muon barrel chambers, where they cover the range 1.0 to 1.25 in pseudo-rapidity. Following the notation of the precision chambers, these stations are called EIL4. Each of them is assembled and pre-commissioned in building 180 and the installation is performed with the Muon Barrel chambers. In the standard assembly procedure, the EIL4 stations are inserted along the rails of the BML stations, then rotated by 90 degrees to their final orientation, and finally positioned along the radial direction. The picture below was taken during the rotation of the station in sectors 5 on the A-side.