Transport vehicles that toe the line
Specially designed vehicles have been developed to transport the superconducting magnets and install them in the LHC. The first such vehicle is now undergoing testing in the tunnel.
In the still of night, unusual convoys will snake their way along the LHC tunnel. Beginning in 2004, five electro-hydraulic convoys will transport and install the 1232 superconducting dipoles and 424 quadrupoles of the LHC's short straight sections (SSS). The vehicles will take over from the familiar monorail used for LEP installation. With magnets that are heavier, longer and much more fragile than those of the old collider, the LHC required an innovative transport solution, especially since the narrow diameter of the tunnels makes the procedure even trickier. In the end, special convoys, each consisting of two tractors, a trailer and unloading equipment were built to a unique set of specifications.
A key feature of the convoys is their infrared optical guidance system which can follow a white line painted on the tunnel floor. Precision guidance is needed to offset the minimal clearance available inside the tunnels: less than 20 cm on either side of the vehicles! This guidance system is not only safer, but also less tiring for the driver. Operations will take place at night, with all convoys departing from PM12 to head for the magnet installation site. As the LHC has a 27-km circumference and the convoys move at a speed of 3 km/h, some trips will take several hours. Even though the transport is automatically controlled, operations will be monitored by a technician. He will take over the controls to unload and install the magnet, which will be raised slightly by the unloading equipment and loaded onto a transfer table before being shifted laterally into position. On completion of the installation sequence, the convoy forms up again and returns to its point of departure.
The vehicles have to cope with the relatively fragile LHC magnets. "The vehicles are designed to minimize vibrations during transport," explains project engineer Keith Kershaw (EST/IC). Indeed, the insulating supports on which the magnets are mounted inside the cryostat are quite fragile, and it is important to minimise the risk of deterioration of these supports or of any modification of the magnet geometry inside the cryostat.
Vehicle construction was entrusted to a German consortium consisting of the firms Babcock Noell Nuclear (W rzburg) and MAFI (Tauberbichofsheim). The transfer tables, which will be delivered this summer, are being supplied by a Slovakian company, ZTS VVU Kosice.
To conduct all necessary tests on the first vehicle, a prototype quadrupole (SSS) was lowered down into the tunnel at Point 4 on 4 March 2003. Nine metres long and weighing in at 9 tonnes, the magnet was loaded onto the trailer, providing a realistic scenario for testing the loading and offloading procedures. "During transport, we took measurements to assess whether the magnet's insulating supports were subject to any impact or deformation. This is one of the tightest constraints on this type of transport," observes Kurt Artoos, who is in charge of acceptance and vibration testing (EST/IC). Operating the convoy in the tunnel also provided an opportunity to test the optical guidance system in situ. The installation of a cryodipole vacuum tank in a section of the tunnel also allowed an assessment of the clearance available for the vehicles. Finally, these trials provided an opportunity to verify the infrastructure that the convoys will use, since the vehicles will for instance be powered via the monorail and its power supply system. To this end,
4 km of monorail and its power supply are being reinstalled in the zones where it had been dismantled for civil engineering work or for the installation of LEP 200. The tunnel floor is also being repaired to minimize the risk of impacts to the magnets. Testing of the first two convoys will continue until late April 2003. All convoys are scheduled for delivery by the end of this year.
