Civil engineering work to enable the installation of the FASER experiment in TI12, which is the former LEP injection tunnel from the SPS, successfully completed this month. The FASER experiment is designed to detect new physics particles produced by the LHC at Point 1. To detect any long-lived weakly interacting particles produced, the FASER experiment must be located exactly on the line of sight of the point 1 ATLAS experiment collision axis. Civil engineering work aimed to create the 6.6 by 1.4m space reservation in the tunnel floor. 

Figure 1: 3D model showing the experiment in place along the beam axis following CE enabling works.

Civil engineering works are not easily carried out in laboratories and CERN is no exception. To allow works to be undertaken without disrupting the LHC, a large airlock to contain any dust and moisture effects has been installed. The works site is put under negative pressure to ensure any air currents flow into the area, not out. We also had to minimise the dust and vibration produced using water suppression techniques when carrying out diamond tip saw cutting or coring to create the required experimental space. 

Figure 2: View of TI12 at current stage in CE works looking down the slope towards the LHC.

Works have been carefully planned to avoid any instability, despite excavation up to around 1m deep in the tunnel floor. In order to manage the possible ground constraints during/after excavation, a 3D Model was created to understand the geotechnical behaviour of the surrounding rock and tunnel.

During works, we nevertheless monitored for any movement. A total of 28 targets are automatically scanned every 2 hours so we know TI12 is still where it should be. We also had to ensure that the existing drainage systems operate during works, despite the fact they will be severed during works. To do this, a dam to catch water had been installed at the upstream end. There is a float in the dammed section which operates like a toilet so when water reaches a certain level, a pump is activated to ‘flush’ the water around the works site and back into existing drains. 

Figure 3: Views showing the airlock looking from LHC towards TI12.

Works were planned and managed by the SMB-SE Future Accelerators Section. The contractor, Dimensione, completed construction on schedule. Following completion, the site will be handed over for the integration and detector installation work packages.