Tasks and structure of the Wendelstein 7-X control system

The superconducting stellarator Wendelstein 7-X will run pulses of up to 30 minutes duration with full heating power. Short pulses with arbitrary intervals, steady state long discharges and arbitrary sequences of short phases with different characteristics in one discharge will be supported by the control system. 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 permitting autonomous operation for commissioning and testing. During the experimental sessions the activity of these devices will be coordinated by a Central Control System and the machine runs more or less automatically with predefined programs. The programs are series of so called “segments”, which define the parameters and the dynamics of the system during each section of a discharge. Segment control is performed by a central sequence controller and local segment control computers. These units generate software objects from the segment descriptions which were previously generated by a special editor and stored in a database. A session leader program allows the leader of the experiment to choose and chain segments, to start or stop a segment chain as a discharge. The progress of the discharge is shown by a sequence monitor attached to the central sequence controller and the session leader program. W7-X has to be prepared for the experiment and monitored by means of the PLC based operational management system. This includes baking and conditioning of the vessel as well as preparing all technical components and diagnostics. A safety system working independently of the operational management consists of local units responsible for the safety of each component and a central unit ensuring the safety of the whole W7-X system. This safety system provides interlocks and controls the human access to the device. A safety analysis is the basis for the development of the safety system. A Trigger-Time-Event system (TTE system) produces a precise time with 20 ns resolution. Time information and event messages are distributed from the central TTE system to the local TTE systems via the TTE net. All other control signals are distributed by Ethernet. A dedicated Ethernet is provided for real time signals