Flexibility aspects of a large real-time control system [JET]

JET is one of the largest fusion experiment in the world. Its main objective is to study plasmas in conditions approaching those required for a fusion reactor. A network of 20 minicomputers forms the backbone of the control and data acquisition system (CODAS) for the JET machine. CODAS processes in real time more than 30000 signals to and from the machine. The main functions include centralised control and monitoring of the machine and collection and storage of up to 15 Mbyte of data from each experimental pulse. This data is transmitted to an off-site IBM/CRAY main-frame complex for off-line data analysis. Because of the character of the experiment the system must also be capable of extensions and fast reconfiguring to handle new equipments and functions. The paper briefly describes the general architecture of the system. It then concentrates on the flexibility aspects built into the system, from hardware to man-machine interface. Tools to manipulate, reconfigure and change the function of the system are explained. Methods and procedures to guarantee the quality and control the charges of software are described. The paper also discusses how other properties like performance and reliability are affected by the built in flexibility