ASDEX Upgrades New Plasma Control Scheme

ASDEX Upgrade is a medium sized tokamak experiment investigating highly shaped plasma and advanced scenarios to be extrapolated for ITER. Eleven independent magnetic coils allow for proper shaping and plasma current control. For plasma heating and current drive eight NBI beam lines, two ICRH antenna pairs and four ECRH gyrotrons are available. Five channels for controlling gas valves and a pellet injector serve for fuelling. All actuators are driven by a digital discharge control system. One basic enhancement of the latest generation is a unified framework for all feedforward and feedback control tasks in a discharge. The framework consists of two layers. The core layer implements wind-up safe feedback controllers with a collection of overlayed output limitations. Each controller is dynamically switchable in references, controlled variables, control law and control parameters via a control mode. The coordination layer implements intelligent discharge protection or optimisation algorithms which synchronously can change control modes and dynamically can generate reference waveforms adapted to the discharge's state and goal. The core layer comprises the backbone of plasma control. Current, shape, heating and fuel control all use a library of highly configurable single- and multivalriable control laws. P, PI and PID controllers are standard components but state space and sliding mode policies can easily be supplemented, too. Likewise, a broad selection of output limiters is available in the library. It ranges from constant values to rate limiters, and multi-signal dependent polynomial characteristics. The controller is aware of any output limitation and can take anti-wind-up measures. Furthermore, a feedforward policy allows to tune the behaviour upon mode transitions, like smooth adaptation or freezing the last output. With the coordination layer, tasks like marfe protection, power exhaust protection and soft pulse termination are accomplished. These specialised algorithms are plugged into the framework using a common interface. The framework approach easily allows for further extensions and opens a door for future experimental investigations