LHCb: on road and under surveillance
The LHCb's RICH2 detector, the larger of two Ring Imaging Cherenkov detectors, has been successfully installed at the site of the LHCb experiment.
A delicate and complex operation that had taken place during night and day finished on Saturday 19th November at 6 pm, when the RICH2 detector took its place in the LHCb experiment.
The RICH2 weighs 30 tonnes (70 tonnes when including its dedicated base support), and is 7.4 metres high (8.7 m when mounted on the trailer). The sheer bulk of the detector was just one aspect of the highly intricate technical operation to transfer the RICH2 detector from the CERN Meyrin site to its final location underground at Point 8 of the LHC ring.
Contained within RICH2 are arrays of finely aligned mirrors. Once the experiment is underway these will focus Cherenkov light, created by charged particles traversing the detector, onto photon detectors.
To prevent these mirrors being misaligned, the convoy carrying the detector had to negotiate the 8 km journey at just over walking pace. A team of computer experts took their places on the convoy with laptops connected to a network of monitoring equipment in order to control the levelling of RICH2 and to record any shocks or accelerations that could possibly have affected the position of the mirrors.
To reduce the risk of discharge from the power lines along the way, power was reduced on the main overhead 400 kV transfer line that crossed paths with the RICH2 route. Furthermore, another electric line of around 20 kV had to be physically lifted by technicians from the electricity company to make way for RICH2 as it passed underneath.
Perhaps the main hazard for RICH2 was the weather. There was the possibility of damage from strong winds, but the main problem was to prevent water condensation on the surface of the mirrors. Large quantities of dry inert gas were therefore injected into the RICH2 vessel throughout the journey. This prevented dew from forming, which could have damaged the reflective coating on the mirrors.
However, during the journey, a problem did arise with a wheel axle of the convoy. This caused unscheduled stops which resulted in a delay from Tuesday to Thursday night. Fortunately, tests by the computer specialists on the convoy showed that there was no damage to the detector, enabling the journey to be completed.
The subsequent task of lowering RICH2 into the cavern on Friday night was in itself a feat of technical wizardry that required millimetre precision.
It is a magnificent achievement for all involved in the RICH2 project, from the building to the transportation stage,' said Christoph Frei of the LHCb collaboration.
Due to constraints on the availability of space and time, RICH2 had to be built in Meyrin, away from the LHCb site. Its final positioning on Saturday marked a successful end to an epic journey for the RICH2 team and everyone collaborating in the project.
