Real-time diagnostics at ASDEX Upgrade—Integration with MHD feedback control

At the ASDEX Upgrade tokamak experiment, a new feedback control loop is under construction with the aim of stabilizing magneto-hydrodynamic (MHD) instabilities, such as neoclassical tearing modes and sawteeth. It uses the mirrors of the electron cyclotron heating (ECH) launchers, which can be steered in real-time to guide each beam to the position needed to stabilize and suppress the mode. The control system needs highly specialized plasma state information such as island position and ECH beam deposition locations in real-time. Data from several diagnostic systems, like electron cyclotron emission (ECE), magnetic measurements and motional Stark effect must be combined in real-time to obtain the required information. These systems strongly differ in sampling characteristics and time resolutions. High sampling rates as 2 MHz for ECE are often required to provide enough data for correlation or frequency analysis. On the other hand, complex analysis methods, such as equilibrium and profile reconstruction, may operate on slower rates of some milliseconds and need tight interaction with measurement systems and high computing power. In this paper, we describe a concept for distributed real-time diagnostic data handling, integration of data from several asynchronous diagnostic systems, and connection to the discharge control system for a broad spectrum of requirements. The system is structured into distributed diagnostic computer clusters, a real-time signal server to combine all information, and the discharge control system. While the focus is currently on MHD control, further real-time diagnostic related applications will be added in future.