Progress in real-time feedback control systems in RFX

Major modifications of the RFX load assembly and power supplies are in progress to allow extensive active control schemes, such as equilibrium and plasma position control and innovative control of the MHD modes. The digital control system is implemented in VME64 using a distributed architecture. The use of a ‘stable’ operating system that is likely to survive some generations of processors can help coping with evolution of technology. PowerPC and Pentium processors were thus considered as candidates and tested and the first one has been selected due to the better performance in floating point computation. Wind River VxWorks has been chosen as real-time operating system. 100 Mbit switched Ethernet has been evaluated for real-time communication by using the user datagram protocol (UDP). Measurements have been executed on a prototype system to assess data transfer latency, jitter and reliability and the results confirm that the solution is suitable for the application. The paper describes in detail the reasons for the choice in the hardware components. Results from several tests comparing the performance of different solutions are also provided.