The original control system for the poloidal field coil power supply (PFPS) in the JT-60 tokamak was developed in 1984. It was composed of CAMAC-based 16-bit microcomputers and I/Os. The control system had been often modified to cope with the tokamak experiments and had been favorably in operation. However, hardware troubles had been gradually increasing due to deterioration of the components such as crates, modules and signal conditioners, etc. It had become difficult to obtain repair parts such as old-type ROM chips with small capacity. Moreover, the software development tools for the microcomputers were not so efficient as those for the modern computers. The cost of the maintenance and the software development in the control system had increased consequently.

It was required to improve the performance of the PFPS control system corresponding to the upgrade of the JT-60 tokamak and R&D*s of super conducting magnets. From the viewpoints of solving the above difficulties in addition to these requirements, we have rejuvenated the control system utilizing the advanced technologies of VME, networks and UNIX-workstations. In the new system, two VME-based 32-bit microcomputers (MC68030) are used as front-end computers for monitoring and control of the devices in the PFPS respectively. Each microcomputer is connected to plural CAMAC crates through its original serial highways. A CAMAC handler written in the language C has been developed for the data transfer in these local control system. Two UNIX-workstations were provided for data handling and sequential control of the PFPS. They are also used as man/machine interfaces for local operation of the PFPS. They are connected to the VME racks and their supervisory central computer system through Ethernet LANs. The same type VME-based microcomputers as those used for the device control and monitoring was applied to the direct digital control of the magnet coil currents.

The renewal of the PFPS control system gave rise to significant improvements in its control performance and software development environment. The operational experience of the new control system will be presented in addition to how we developed it by applying the modern computer technology.