26 July 2011
The RIKEN-RAL Muon Facility is a joint venture between RAL and Japan’s RIKEN (Institute of Physical and Chemical Research). The facility uses an 800 Mega electronVolt (MeV) proton beam, which strikes a graphite production target, creating nuclear reactions that produce a type of subatomic particle, known as pions. These pions are then directed into a superconducting magnet, where they decay into muons, another type of short-lived particles which are used in a number of experiments around the facility. The magnet needs to be kept at less than 80 Kelvin to maintain its superconducting properties, achieved by a cryogenic system using liquid helium. Maintaining a superconducting state gives a very low resistance. This cuts the current losses, which would otherwise manifest as heat, making its operation more affordable and giving a stronger magnet for a given current.The cryogenic system was controlled by an ABB SATT control system, installed in the mid-1990s. This aging controller has since been phased out. RIKEN and RAL chose to upgrade the control system with the latest ABB Compact 800 series. The new controller provides control of valves in the cooling system to ensure that the correct amount of liquid helium is being injected to achieve the correct low temperature. Another major part of the project was the installation of an ABB’s new software based human machine interface (HMI), Compact HMI, which gives data about the process, so that both current behaviour and trends can be determined.Jeremy Moor, a control engineer who provides support for the cryogenic system, says: “The new control system gives much more data on the condition of the cryogenic system. “It provides tools that we can use to examine performance, helping us to determine what is going on with individual components. For example, I can look back to a cool down we did last September and compare it with how the system is behaving now. The other system was purely control only and did not provide the detailed data that we have now. We can see the effect of operating various valves and see which valve has what effect. The coolant supply is the life of the facility – without it we cannot produce muons and so cannot do any science.”One of the major issues was a problem with one of the helium valves. This was thought to be a leak but no-one could be sure because the existing system did not provide enough information to confirm this. The new control system has helped Moor investigate the problem with the valve: “We had lost cooling power and originally thought it was due to the valve leaking gas, but the new control system has lead us to believe the problem could lie elsewhere. We have already used it to solve some mechanical issues as well as updating some interlocks to improve safety.”Another feature of the control system that Moor has found useful is the GSM alerts. During a cool down phase, the cryogenic system takes several hours to cool the magnet to the correct temperature. If a failure occurs, in a valve for example, it could be many hours before the fault is discovered. The magnet will begin to warm up again, causing serious delays to the experimental schedule. The GSM alert feature sends a text message to a mobile phone if such a fault is discovered, allowing the problem to be addressed and solved in minutes rather than hours.ABB supports the installed hardware and software through its Sentinel maintenance program, which maintains systems as needed and updates hardware and software when new modifications or products are released.
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