R. Merkel

Real-time feedback control of the plasma density profile on ASDEX Upgrade

The spatial distribution of density in a fusion experiment is of significant importance as it enters in numerous analyses and contributes to the fusion performance. The reconstruction of the density profile is therefore commonly done in offline data analysis. In this paper, we present an algorithm which allows for density profile reconstruction from the data of the submillimetre interferometer and the magnetic equilibrium in real-time. We compare the obtained results to the profiles yielded by a numerically more complex offline algorithm. Furthermore, we present recent ASDEX Upgrade experiments in which we used the real-time density profile for active feedback control of the shape of the density profile.

ASDEX Upgrade MHD Equilibria Reconstruction on Distributed Workstations

The identification of MHD equilibrium states on the ASDEX Upgrade tokamak is a prerequisite for interpreting measurements from a wide range of diagnostics which are correlated with the shape of the plasma. The availability in realtime of plasma parameters related to the MHD state is crucial for controlling the experiment. Function Parameterization is used as a standard tool to determine the position, shape, and other global parameters of the plasma as well as the MHD equilibrium flux surfaces. The recently developed interpretive equilibrium code CLISTE now enables the calculation of MHD equilibria on an intershot timescale. These calculations are parallelized by the use of a Message Passing Interface (MPI).

Review of the ASDEX Upgrade data acquisition environment - present operation and future requirements

The data acquisition environment of the ASDEX Upgrade fusion experiment was designed in the late 1980s to handle a predicted quantity of 8 Mbytes of data per discharge. After 7 years of operation a review of the whole data acquisition and analysis environment shows what remains of the original design ideas. Comparing the original 15 diagnostics with the present set of 250 diagnostic datasets generated per shot shows how the system has grown. Although now a vast accumulation of functional parts, the system still works in a stable manner and is maintainable. The underlying concepts affirming these qualities are modularity and compatibility. Modularity ensures that most parts of the system can be modified without affecting others. Standards for data structures and interfaces between components and methods are the prerequisites which make modularity work. The experience of the last few years shows that, besides the standards achieved, new, mainly real-time, features are needed: real-time event recognition allowing reaction to complex changing conditions; real-time wavelet analysis allowing adapted sampling rates; real-time data exchange between diagnostics and control; real-time networks allowing flexible computer coupling to permit interplay between different components; object-oriented programming concepts and databases are required for readily adaptable software modules. A final assessment of our present data processing situation and future requirements shows that modern information technology methods have to be applied more intensively to provide the most flexible means to improve the interaction of all components on a large fusion device.

Recent Developments in the ASDEX Upgrade Data Acquisition Environment

Abstract ASDEX Upgrade today delivers approximately 25 GBytes of data per week. To manage this demand, which in fact is a growth by a factor of two in the last 2 years, several improvements to the data acquisition (DAQ) system have been made to avoid bottlenecks and to enhance the usability. Modifications were done to the diagnostic clients to speed up the storage of big diagnostic files to the central analysis server. The diagnostic synchronization server has been modified to handle wait requests not only for raw but for any level of evaluated data files. The central analysis server has been upgraded to deliver the power to do synoptic data analysis on up to 500 MBytes/shot on a single multiprocessor machine in shared memory. Additionally a cluster of ten workstations for parallel applications has been built up for MHD equilibrium calculations and other CPU-intensive tasks. The Andrew File System (AFS) archive servers have been upgraded to more disk capacity, a redundant storage architecture and faster network connections. However, as a basis for these improvements the network backbone and the server connections have been moved from FDDI to Gigabit-Ethernet and single workstation connections from Ethernet to Fast-Ethernet. Performance analysis results give an impression of the achieved improvements. Other projects in conjunction with the DAQ system at ASDEX Upgrade are the ‘hotlink’ interface system development for the Soft-X-Ray and Mirnov-Probes diagnostics and the ‘S-link’ development for an enhanced electron cyclotron emission (ECE) diagnostic. Both will serve as prototypes for future real-time diagnostics, which shall be able to deliver processed data in real-time to other systems — especially experiment control — to achieve a possibly better experiment performance.

Integrating discharge control and data acquisition at ASDEX Upgrade

ASDEX Upgrade is being equipped with new plasma controllers and advanced diagnostics. These will be integrated into a distributed system, exchanging process data and plasma state information via a real-time network. Infrastructure tasks on dedicated nodes represent a functional framework for embedding of applications. Any type of hardware or operating systems may implement these, as long as the general rules on I/O timing and signal exchange methods are observed. To avoid temporal uncertainties in the measurement process a new time system was designed. Time becomes a measurement quantity sampled with data and process values.

Real-time information exchange between data acquisition and control systems at ASDEX Upgrade

Todays data acquisition systems and control at the ASDEX Upgrade fusion experiment communicate during the setup of an experimental discharge only. While control executes the discharge based on recipes and a fixed number of input and output channels, diagnostic measurements are done under a predefined schema. Considerable benefits for scenario specific discharge execution are expected to be drawn from a real-time integration of data acquisition and discharge control systems: Information from the control system can be used for the real-time adaptation of the data acquisitions configuration, such as channel selection, time resolution, signal filtering, analysis process selection and protocolling functions. Information from data acquisition processed from the full set of input channels and diagnostic-specific knowledge can be used to select and fine-tune control configurations. Access to the data acquisition systems as external information sources potentially reduces the complexity of the discharge controls peripheral hardware and preprocessing software. Information exchange among these systems on a peer-to-peer basis allows freely to communicate the results. This is preferable to a master-slave concept where strict communication protocols have to be observed. In this paper we present the current work on the integration of discharge control and data acquisition at ASDEX Upgrade and give an outlook on future developments.