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Visualization of measurements together with experimental settings is a general subject in experiments analysis. The complex engineering design, 3D geometry, and manifold of diagnostics in larger fusion research experiments justify the development of special analysis and visualization programs. Novel ASDEX Upgrade (AUG) software tools bring together virtual navigation through 3D device models and advanced play-back and interpretation of video streams from plasma discharges. A third little tool allows the web-based platform independent observation of real-time diagnostic signals. While all three tools stem from spontaneous development ideas and are not considered mission critical for the operation of a fusion device, they with time and growing completeness shaped up as valuable helpers to visualize acquired data in fusion research. A short overview on the goals, the features, and the design as well as the operation of these tools is given in this paper.

In fusion research the ability to generate and sustain high performance fusion plasmas gains more and more importance. Optimal combinations of magnetic shape, temperature and density profiles as well as the confinement time are identified as advanced regimes. Safe operation in such regimes will be crucial for the success of ITER and later fusion reactors. The operational space, on the other hand, is characterized by nonlinear dependencies between plasma parameters. Various MHD limits must be avoided in order to minimize the risk of a disruption. Sophisticated feedback control schemes help to tackle this challenge. But these in turn require detailed information on plasma state in time to allow proper reaction. Control system and diagnostic systems therefore must establish a symbiotic relationship to carry out such schemes. Today, all major fusion devices implement such a concept. An implementation of such a concept with sustained integration is presented using the example of ASDEX Upgrade. It covers data communication via a real-time network, synchronization mechanisms for data-driven algorithm execution as well as operational aspects and exception handling for failure detection and recovery. A modular distributed software framework offers standardized user algorithm interfaces, automated workflow procedures and the application of various computer and network hardware components. Designed with a special focus on reliability, robustness and flexibility, it is a sound base for exploring ITER-relevant plasma regimes and control strategies.

A universal time to digital converter (UTDC) and a digital I/O (DIO) card have been purpose-built for the new ASDEX Upgrade control system, the Thomson scattering diagnostic, a renovation of the magnetic measurements, and a couple of other diagnostics requiring renewed timing or real-time features. The principal features of these cards are presented and it is shown how synergy in hardware and software development was achieved. Examples of actual usage in diagnostics are given. Measurements of the real-time behaviour of cPCI-based diagnostics show low jitter of the Solaris operating system and highly reliable operation under moderate real-time conditions. Future applications of this family of cards are foreseen.

ASDEX Upgrade is being equipped with a new real-time plasma control and data acquisition system and a novel time system. Major components were implemented and installed. While much work for performance optimisation and application programming remains to be done, commissioning of the new system parallel to experiment operation is being prepared. Commissioning of the new system will be done step-by-step. To facilitate testing the old and new control systems share all input signals. Switching between old and new system can be performed within 60 min: 23 fibre optics for output of actuator commands and input triggers must be connected to the active system and minor modifications done to interface the machine protection. Commissioning phases include background listening, technical discharges and full plasma operation. With the strategy chosen we minimize risk to the machine and reduce interference with ongoing experiment campaigns.

Fast data acquisition with direct transfer to memory is facilitated by the S-LINK interface protocol, developed at CERN, the European Organization for Nuclear Research. The need for customized hardware development reduces to application-specific front-end interfaces. Two applications of S-LINK data acquisition systems for microwave Doppler reflectometry and electron cyclotron emission radiometry at the ASDEX Upgrade nuclear fusion experiment are presented.

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.

It has been a while since it had been reported on the status of ASDEX Upgrade data acquisition (DAQ) and data management environment. An update on changes, expansions, and enhancements applied in the last years will be given. The acquired amount of data per shot increased from 4 GiB to 40 GiB in eight years. Network, storage, and archive challenges have been managed by stepwise improvements. New DAQ techniques have been introduced to replace outdated technologies. Real-time diagnostics speed-up data provisioning and contribute to feedback control. Information technology applied to ASDEX Upgrade is under permanent change. Recent and future steps are outlined.

We discuss the circuit design of a digital multiradian phase detector that measures the phase difference between two 10 kHz square wave TTL signals and provides the result as a binary number. The phase resolution of the circuit is 1/64 period and its dynamic range is 256 periods. This circuit has been developed for fusion plasma interferometry with submillimeter waves on the ASDEX Upgrade tokamak. The results from interferometric density measurement are discussed and compared to those obtained with the previously used phase detectors, especially with respect to the occurrence of phase jumps. It is illustrated that the new phase measurement provides a powerful tool for automatic real-time validation of the measured density, which is important for feedback algorithms that are sensitive to spurious density signals.

To improve the plasma position and shape control system in ASDEX Upgrade, it is constantly expanded by the integration of data acquisition systems of important and interesting diagnostics. Usually the main responsibility of data acquisition systems is to collect data and subsequently put it into a data base archive system from where it is later analysed. The obligation now is also to simultaneously process the acquired data with an appropriate algorithm and send the pre-processed data in real-time to the plasma control system during a discharge. To achieve this requirements the used hardware must provide enough processing power and the operating system has to meet some real-time constraints. To avoid the burden of using proprietary real-time operating systems the trend is to use Open Source variants mainly based on Linux. Some of these solutions also allow us doing real-time capable communication using standard Ethernet hardware. By way of an example the implementation process of a prototype of a real-time data acquisition system based on a multi-core processor and Xenomai is demonstrated. Other possible solutions like Realtime Linux and their differences to Xenomai which we propose as the most sophisticated real-time framework for Linux are discussed in this paper.

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Today's 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.

On ASDEX Upgrade a concept for real-time stabilization of NTMs has been realized and successfully applied to (3,2)- and (2,1)-NTMs. Since most of the work has meanwhile been published elsewhere, a short summary with the appropriate references is given. Limitations, deficits and future extensions of the system are discussed. In a second part the recent work on using modulated ECCD for NTM stabilisation is described in some detail. In these experiments ECCD power is modulated according to a magnetic footprint of the rotating NTM. In agreement with earlier results it could be shown that O-point heating reduces the necessary average power for stabilisation whereas X-point heating hampers stabilisation. Although this modulated scheme is not relevant for routine NTM stabilisation on ASDEX Upgrade it may be mandatory for ITER or DEMO. On ASDEX Upgrade it has been re-developed to demonstrate the usage of a FAst DIrectional Switch to continously heat the O-point of the rotating island with only one gyrotron switching between two launchers which target the mode at locations separated in phase by 180 degrees as described in [1].

The availability of high power lasers with average power levels above 5 kW and high beam quality triggered a number of industrial applications of lasers. Especially the process of deep penetration welding made the use of lasers attractive in applications where low distortion and small heat affected zones are required. In deep penetration welding a channel, called keyhole, supported by the pressure of evaporating material is formed by the laser beam, which allows the radiation of the laser a direct access to deep layers of the material. This is in contrast to conventional welding, where the heat either has to diffuse from the surface to the bulk material by heat conduction or the heat must be allowed to reach deeper layers by pro-viding a direct access using a preformed chamfer which has to be closed by filler material. By moving the laser beam relative to the material, the keyhole is driven parallel to the surface. The material molten at the front of the keyhole flows around the keyhole and resolidifies in its wake. The diameter of the keyhole and the thickness of the fluid layer necessary to support the flow around the keyhole determines the minimum width of the molten area and the width of the heat affected zone and hence the minimum energy per unit length of the seam if deep penetration laser welding is used.

Due to the material properties like high reflectivity high thermal conductivity low ionisation energy aluminium is weldable by CO -Lasers only under appropiate conditions. Possibilities to increase the energy coupling will be discussed in this paper. The suitable application of assist gas is one possibility. Hereby it is necessary to accomodate the composition of the assist gas supply to the process parameters (beam intensity, focal length, welding speed, material composition and so on). With optimized parameters it is possible to weld aluminium sheets of thicknesses > 6mm.

From the laser beam cutting of metals, a strong effect of the beam polarisation referring to the cutting direction is known. In laser welding this effect is relatively unknown. Experimental results show that a strong polarisation effect could take place in deep welding too if some threshold conditions are fulfilled. Using the right beam polarization e.g. pipes could be welded quicker than with an unpolarized beam.It is possible to weld pipes or plates much faster than with normal keyhole welding if the beam polarization is used in a way that the beam is guided to the joining point. This technique is presented in this paper.From the laser beam cutting of metals, a strong effect of the beam polarisation referring to the cutting direction is known. In laser welding this effect is relatively unknown. Experimental results show that a strong polarisation effect could take place in deep welding too if some threshold conditions are fulfilled. Using the right beam polarization e.g. pipes could be welded quicker than with an unpolarized beam.It is possible to weld pipes or plates much faster than with normal keyhole welding if the beam polarization is used in a way that the beam is guided to the joining point. This technique is presented in this paper.

Welding of pipes and manufacturing of plated metal sheets are two applications of a laser beam in which the distribution of the absorbed intensity differs considerably from the irradiation. Laser beam propagation between two adjoining metal surfaces is investigated experimentally and the results are compared with theoretical calculations. The radiation transfer equation is solved for the redistributed laser intensity at the adjoining metal surfaces. The influence of beam radius, polarization state and transversal disadjustment are discussed.

Densities achievable in ASDEX Upgrade discharges are restricted by a disruptive limit in the L-mode caused by an edge-power imbalance which is linking divertor detachment, Marfe formation and the separatrix density. The attainable average densities depend then on the internal particle sources and the core transport and can exceed the empirical Greenwald density. In H-mode an upper density limit is found which represents a non-disruptive H - L back transition, which is preceded by the occurrence of type-III ELMs. Close to the Greenwald limit this H - L transition cannot be avoided at any power flux across the separatrix and - at high external neutral gas fluxes - confinement compared with ITER H-92P scaling degrades even before the back transition. The H-mode operational window is determined by local edge-barrier parameters and their gradients, respectively. The boundaries are represented by the L - H transition-temperature threshold, the ideal ballooning edge-pressure gradient limit, the upper temperature limit for type-III ELMs and an upper H-mode barrier density limitation. The cause for the last limitation is not yet identified; it may be due to resistive ballooning modes or the separatrix density limit. Despite the limited edge densities the Greenwald density could be surpassed by a factor of three with pellet refuelling from the low magnetic-field side. Pellet injection from the high-field side gains from the strong increase of fuelling efficiency due to the assisting toroidal outward drift of the formed high- ablatant. Higher densities are achievable in H-mode compared with low-field side injection and diminished convective losses avoid confinement degradation up to the Greenwald density. In gas-puffed type-I ELMy H-modes the plasma thermal energy and the edge-pressure gradients, which are limited by ballooning stability, are linked via a robust temperature-profile stiffness and the flat density profiles resulting from dominant edge refuelling at high densities. Their confinement does not improve with increasing density (and neutral gas fluxes) and may even slightly degrade. Therefore, the superior confinement of type-I ELMy H-modes compared with type-III ELMy ones at medium densities is actually offset at densities close to the Greenwald density. In contrast to the temperature-profile resilience density profiles can be changed both by deep refuelling (with pellets) and intrinsic transport improvements connected with density peaking (observed in CDH-modes), which offers the combination of high confinement and high density operation. The possible alliance with radiation cooling, divertor detachment and divertor compatible type-III ELMs could solve the power exhaust problem.

For applications of advanced plasma control schemes, many computers that execute complex algorithms need to communicate with low latency so that result data are promptly available for operating ade...

ASDEX Upgrade (AUG) since many years has been using a built to purpose FPGA PCIe computer interface with fast serial interconnects – called “SIO” – connecting to peripheral crates based on a pipeline organized backplane – called “Pipe” [ 1 ] 1 – containing modular DAQ devices. The combination of custom built input channels, aggregated into multi-channel FPGA controlled backplanes and streamed by one or more SIO2 FPGA cards via DMA into computer memory enables the deterministic delivery of data for real-time applications with minimum latency. The renewal of large diagnostics for the Mirnov probes, the Soft-X-Ray cameras and others have been successfully conducted. These diagnostics have undergone the transition from Solaris to Linux CentOS with real-time kernel. These systems, receiving a stream of measured samples from the SIO2 periphery via DMA, directly provide data for plasma control via sharing the DMA memory sections with dedicated application processes (APs) running on the same node as part of the AUG distributed discharge control system [ 2 , 3 ]. The SIO2 DAQ is further applied to a Thomson-Scattering (TS) system located in the AUG Divertor (DTS). New GigaSample ADCs developed for this diagnostic expand the range of measuring periphery into the GHz range. The same ADCs are planned to be used to refurbish and real-time enable the main chamber Thomson-Scattering system. The paper describes the concepts of the “Pipe2” periphery and the “SIO2” interface card. It briefly summarizes specifics of the diagnostics mentioned above and puts further emphasis on design modifications of the FPGA firmware to address new requirements. It will also give a short description of the developed GSPS ADC/FPGA periphery cards.