Real Time Software for the Fusion Experiment WENDELSTEIN-7-X

The super conducting stellarator WENDELSTEIN 7-X will run pulses of up to 30 minutes duration with full heating power and even longer ones with reduced heating. All discharge scenarios compatible with these capabilities will be supported by the control system: short pulses with arbitrary intervals, steady state discharges and arbitrary sequences of phases with different characteristics (“segments”) in one discharge [1]. The hierarchical layout of the control system will reflect the structure of the experimental device. Each technical component and each diagnostic system including its data acquisition will have its own control system. In general each control system but that for data acquisition bases on a real time computer, i.e. a PC running the operating system VxWorks®, permitting autonomous operation for commissioning and testing. The activity of these controllers will be co-ordinated in real time by a master controller during the experimental sessions. All these real time computers implement the software package W7X SegmentControl which will be presented in the contribution. By means of this package the real time computers will run cyclically and synchronized at a kHz frequency. The system behaviour as far as it is relevant for the experiment, like parameters and algorithms, will be exclusively controlled by complex software objects. By changing references to these objects synchronously in all computers the whole system behaviour can be changed from one cycle to the next. The control objects can use measured data from any other system available via a real time data bus based on Ethernet. Switching between segments and the end of the discharge will be triggered by the master controller and may be determined by fixed timing, by logic conditions or by operator action. All data required for the construction of the software objects will be stored in one central database and constructed in the control computers during initialisation or operation well before they are required. [1] Laqua, H, Niedermeyer, and H. Schacht J.: Control system of WENDELSTEIN 7-X experiment, Fusion Engineering and Design Vol. 66-68 (2003), pp. 669-673