Open source real-time operating systems for plasma control at FTU

Nowadays, every tokamak has a plasma control system to monitor and drive discharge parameters like position, density, current, and shape. Several different solutions have been adopted to cope with the real-time constraints, ranging from the shared memory to the transputers technologies. At present, a VME/PPC604r embedded controller running a LynxOS operating system is used on Frascati Tokamak Upgrade (FTU) for the plasma position control, with a response time of about 150 mus. In this paper, a report of the tests carried out using the open source Linux real-time operating system RTAI on a VME/INTELx86 embedded controller will be presented, in order to evaluate the replacement of the existing expensive commercial solution for the plasma control system. To this aim, the plasma position control software has been ported on the open source platform. Moreover, the performance of the two real-time operating systems will be compared, both at system level and at application level. The comparison will show that the open source real-time operating system is a good alternative to the commercial product and, because of its hard real-time features, it is a well-guaranteed platform for our plasma control system software.