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

Abstract

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 realtime 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.

Real-time diagnostics at ASDEX Upgrade—Architecture and operation

“…The overhaul of the AUG Control System completed in 2006 [5], opened the possibility of feeding externally acquired and preprocessed data as RT inputs to performance optimization processes [6]. This led to a demand for delivery of results from RT DAQ and RT Analysis as input into Control.…”

Real time magnetic field and flux measurements for tokamak control using a multi-core PCI Express system

“…In addition to the magnetic flux surfaces, the electron density profile and microwave beam tracing code calculations, TORBEAM [19], are required in real time. Microwave beam refraction by the electron density gradient needs to be taken into account to steer the mirror to the correct angle for ECCD power deposition on the targeted magnetic flux surface [4].…”

“…The angle required for the mirror to achieve this is a function of the spatial co-ordinates of the rational flux surface. The spatial co-ordinates of the rational flux surface therefore need to be communicated in real time to the control system by the dedicated data acquisition system [4].…”

ASDEX Upgrade CODAC overview

“…operate on timescales of many to many tens of milliseconds [9]. A synchronization scheme has been developed where milliseconds timesynchronized control algorithms can coexist phase-locked with the faster vertical stability control [10].…”