The LHC's equipment all in step

Over 80% of the control equipment for the LHC will be connected by a special communication network known as WorldFIP, which has been chosen for its very precise timing, excellent operating performance and robustness in difficult environments. Over 350 kilometres of this network are currently being installed in the LHC tunnel and checked for compliance with the required standards.

At CERN, the "bus" specialists are using bicycles to cover the 27 km of the LHC tunnel. The buses in question are not motor vehicles but communication buses, also known as fieldbuses, which are the communication networks responsible for the reliable transmission of digital data between the various control components. At present, the teams of network specialists are cycling around the 27 km tunnel to check that the thousands of communication nodes needed for the LHC control system meet the required standards.

A large part of the LHC machine will be controlled by these communication networks. More than 80% of the control equipment in the tunnel uses WorldFIP, a technology complementary to Ethernet. "This bus was chosen for its excellent performance in demanding environments like that of the LHC", explains Raymond Brun, who is in charge of the LHC-WorldFIP project. Controlling the accelerator equipment requires perfect synchronisation.

"Using the WorldFIP bus in conjunction with GPS, we will be able to synchronise most of the equipment around the 27 kilometre circumference of the machine tunnel, automatically adjust its timing and log events to within a few microseconds", he adds. The bus will thus act as a sort of timer for the LHC equipment. Its other great advantage is its excellent resistance to strong electromagnetic noise and radiation, which also makes it well-suited to use in nuclear power plants. Finally, it is capable of high-speed transmission over the long distances separating the components of the LHC accelerator without any signal regeneration.

Since the WorldFIP was chosen in 1996, the support team from the AB Department's Controls Group has been working flat out to develop the network architecture and associated software. The latter will be used to validate the 15000 connections to the 15000 intelligent devices using microcontrollers.

The LHC segments will be controlled by 160 industrial PCs, which will act as the bus arbitrator and run the software needed for data transfer and for the synchronization of equipment with the overall LHC timing system.

Now that this important development stage has been completed, the network is being deployed in the LHC environment. This is no mean feat as it will be used by no fewer than seven main systems, namely magnet protection, power conversion, beam instrumentation, radiofrequency, cryogenics, radiation measurement and magnet positioning.

A total of 350 kilometres of network, comprising 250 communication segments, are currently being installed, representing more than 6000 cables recognizable by their distinctive green colour. The WorldFIP support team is currently cycling around the tunnel to check the compliance of the various segments. For each of them, it will have to perform a series of electrical and dynamic tests to make sure that the performance meets the required communication standards. "We have already checked 18% of the network", explains Raymond Brun, "and will reach a cruising speed that will allow us to check 10% of the network each month by the end of February, so that we stay in line with the overall LHC schedule."

The results are very encouraging as the WorldFIP team was already able to confirm that the network was working properly when the new 2.5 km TI 8 transfer line between the SPS and the LHC was successfully commissioned last autumn.