M. Zilker

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.

A "Universal Time" system for ASDEX Upgrade

For the new generation of intelligent controllers for plasma diagnostics, discharge control and long-pulse experiment control a new time system supporting steady state real-time operation has been devised. A central unit counts time at nanosecond resolution, covering more than the experiment lifetime. The broadcast time information serves local units to perform application functions such as current time readout, trigger generation and sample time measurement. Time is treated as a precisely measured quantity like other physical quantities. Tagging all detected events and sampled values with measured times as [value; time]-entities facilitates real-time data analysis, steady state protocolling and time-sorted archiving.

Reflectometry-based plasma position feedback control demonstration at ASDEX Upgrade

In fusion experiments, real-time feedback control of the plasma position plays a vital role for machine protection and disruption avoidance. This control task is presently performed using magnetic measurements that, in future long pulse tokamak devices of the ITER class, may be affected by drifting integrators or radiation induced voltages in the magnetic pickup coils. These effects could have an impact on the magnetic equilibrium reconstruction, causing potential losses of position control and, consequently, leading to premature discharge termination or plasma-facing component damage. Frequency modulated continuous wave O-mode reflectometry, a non-magnetic dependent technique used to measure the density profile, was proposed to backup or complement the standard magnetic-based control in such devices. This new control scheme has just been successfully demonstrated for the first time on the ASDEX Upgrade (AUG) tokamak. The location of the plasma boundary, used in the control of the plasma column position, was tracked in real-time (RT) using dedicated algorithms and a new approach that combines the reflectometry edge profile and a scaled line integrated density measurement from interferometry. Although feasibility studies on the viability of this method had been previously conducted at AUG, the capabilities required to produce this on-line demonstration were only incorporated in the diagnostic after a recent upgrade of its data acquisition and processing hardware. The results herein presented show the first successful demonstration of the reflectometry plasma position application as proposed for ITER.

The new ASDEX Upgrade real-time control and data acquisition system

Abstract ASDEX upgrade investigates the integration of confinement, stability and exhaust issues into an operating scenario for ITER and a future fusion reactor. Since commissioned in 1990 the systems used to feedback control plasma position and shape as well as performance have continuously been enhanced. To overcome performance limitations and improve connectivity and steady state capability, a new plasma control system is being implemented. For the new system, adequate and reliable communication mechanisms are essential to integrate the realtime discharge control and data acquisition. We present communication methods and the process organisation of the new system and show that the new concept allows easy performance scaling. We demonstrate how existing periphery and new realtime diagnostics interface to control applications. This facilitates the realisation of novel and sophisticated control tasks combining multiple diagnostics and actuators for common physical goals.

Cutting edge concepts for control and data acquisition for Wendelstein 7-X

Wendelstein 7-X is intended to demonstrate steady state high performance plasma operation and to explore the physics basis of the Helias reactor concept. From there, the W7-X CoDaC concepts aim for steady state plasma stabilization at favorite operation points and largely or even fully documented plasma experiments for achieving efficiently scientific results. Several concepts are being employed that are not common to the fusion research so far. The plasma control system is based on segments consisting of control parameters and transition conditions to other segments. The data acquisition system aims at streaming all acquired data for archiving, control and monitoring purposes and tries to prevent early data reduction. This leads to data streaming rates of up to 30 GBytes/s during plasma operation of up to half an hour. The data analyses framework is intended to support largely automation with analyses chains based on service oriented architectures. A coupling to real time systems is envisaged later in the project for solving complex control problems. The envisaged model based data analyses rely on the existence of unanalyzed raw data in combination with a systematic documentation of the experimental setup, in particular for the diagnostics.

COTS based high data throughput acquisition system for a real-time reflectometry diagnostic

Achieving higher levels of plasma performance control in present fusion experiments requires that diagnostics be upgraded to deliver processed physical parameters in real-time (RT). A key element in a diagnostic RT upgrade is the data acquisition system (DAS), that should be capable of delivering the acquired data to the data processing resources with very low latencies and in the shortest possible time. Adequate standard commercial solutions with these characteristics are not easily found in the market, what leads most of the times to the development of complex custom high-performance designs from ground-up. A mixed solution, partially based on commercial off-the-shelf (COTS) components, is under development to upgrade the existing ASDEX Upgrade (AUG) broadband reflectometry diagnostic so that a full demonstration of plasma position control using RT reflectometry density profile measurements can be performed. The 8-channel (12-bit/100 MSPS) DAS being designed features a PCI Express (PCIe) x8 interface to enable direct memory access (DMA) data transfers with throughputs in excess of 1 GB/s. The use of COTS components resulted in a faster hardware design cycle without compromising system performance and flexibility. The architecture of the system and its main design constraints as well as the system integration in the AUG RT diagnostic network are herein discussed. Preliminary benchmark results for data throughput and overall measurement latency are also presented.

Multiprocessor systems for real-time data acquisition on the Asdex upgrade and future plasma experiments

Abstract In this paper we present our transputer-based multitop multiprocessor systems for data acquisition, which are currently used on the Asdex upgrade experiment. The bandwidth of these systems goes from low-speed like the calorimetry diagnostic up to highspeed and large data volume systems like the soft-X-ray and Mirnov diagnostics, which collect several hundreds of megabytes of data during a plasma discharge of ≈8 s. Further, we present the multitop-MX, a newly developed system based on transputers and powerPCs, which provides real-time facilities for analysing the acquired data, to generate necessary information for the dynamic adaptation of sample rates, and to deliver triggers when certain events in the plasma are detected. The algorithm running on the powerPCs performs a wavelet like time-frequency transform. In the last part we give an outlook how to build the next generation of data acquisition systems to be used on the future plasma experiments W7-X and ITER, but also on Asdex upgrade. The hardware of these new distributed systems should be mainly based on established industry standards like the VME-bus, PCI-bus and FiberChannel, but also emerging technologies like SCI (scalable coherent interconnect) should be considered. The systems software should be well designed with object oriented methods to simplify the maintenance process and to enable further expansions and adaptations to new problems in an easy way.

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.

Real time data acquisition with transputers and PowerPCs using the wavelet transform for event detection

In this paper a new data acquisition system for the soft-X-ray diagnostics in a large fusion plasma experiment is described. The main purpose of this system is to provide real time facilities for analyzing the acquired data, to generate necessary information for the dynamical adaptation of sample rates, and to deliver triggers when certain events in the plasma are detected. The hardware is built on a network of up to 72 transputers and up to four modules, each consisting of a PowerPC and a transputer coupled via dual-ported RAM. The transputers are used for collecting the incoming data from ADCs (each sampled with 500 KHz), and for communication and synchronization within the computer network. Four PowerPCs can analyze up to eight selected channels in real time and provide the results to the other transputers in the network. The algorithm running on the PowerPCs is performing a wavelet like time-frequency transform for the detection of plasma events. With this system it was possible to observe high-n/m mode cascades following impurity accumulation. A report on this effect has been published in Physical Review Letters.

A high-speed transputer-based data acquisition system

A 250 MHz 8-bit transputer-based data acquisition VME bus module is described. This module has been designed as the acquisition node of a transputer-based real-time processing and data reduction system for the reflectometry diagnostic in the ASDEX Upgrade tokamak experiment. The architecture of the board is detailed, emphasizing the advantages of using recently delivered devices, like fast synchronous FIFOs, in a mixed ECL/TTL data acquisition architecture. It is shown that the implemented architecture leads naturally to the implementation of hardware triggers that allow the acquisition channels to operate as stand-alone modules in a self-triggered, self-timed, data acquisition mode. The advantages of using transputers as local control and processing units are discussed. The use of the board in the reflectometry diagnostic and the general processing goals of the system are presented together with data characterizing the performance of the acquisition channels.