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The COMPASS-U tokamak (R = 0.894 m, a = 0.27 m, Bt = 5 T, Ip = 2 MA) is a new medium-size device with fully metallic plasma facing components, currently under construction at the Institute of Plasma Physics of the Czech Academy of Sciences in Prague. It features a unique combination of parameters, such as a high temperature of the tokamak walls up to 500 ◦C allowing a high recycling regime, a high magnetic field connected with a high plasma density above 1020 m -3 and with a high heat flux (perpendicular to divertor targets) density at the outer strikepoint up to 90 MW/m2 in attached conditions. These parameters of the device pose strict constraints and requirements on the design of individual diagnostic systems. Strategy and present status of the development of the diagnostic systems for COMPASS-U are provided. Plans for a diagnostic set for the first plasma are reviewed. The review of the diagnostics systems involves the high-temperature compatible slow (up to 20 kHz) and fast (up to several MHz) inductive and non-inductive magnetic sensors (including Thick Printed Copper coils and Hall sensors), the sub-millimetre interferometer with an unambiguous channel, Electron Cyclotron Emission, the interlock and overview cameras, high resolution Thomson scattering, radiation diagnostics (neutron diagnostics, soft and hard X-ray diagnostics, bolometers, impurity monitors, effective ion charge), probe diagnostics (including rail probes) and manipulators.

COMPASS-U, a high magnetic field tokamak with hot walls, will be designed and built at IPP Prague. Unique features of this new device bring noticeable constraints and requirements on plasma diagnostics, which make their development highly demanding. In this paper, the main expected constraints influencing the conceptual design of diagnostic tools for COMPASS-U (high temperature of the vacuum vessel, high plasma density, high heat flux density, strong auxiliary plasma heating, spatial constraints, liquid metals in the divertor) are reviewed and possible solutions are indicated.

A new fast divertor infra-red thermography system was put into operation on COMPASS. It provides full radial coverage of the bottom open divertor with pixel resolution ∼0.6–1.1 mm/px on the target surface and temporal resolution better than 20 μs. The system consists of fast IR camera TELOPS Fast-IR 2K placed in a magnetic shielding box, a positionable holder, a 1 m long IR endoscope consisting of 14 Ge and Si lenses securing off-axis view from an upper inner vertical port and a special graphite divertor tile optimized for IR thermography. The tile is equipped with a heating system allowing tile preheating up to 250 °C. Embedded thermoresistors and a calibration target (a deep narrow hole acting as a black body radiator) allows in-situ calibration of the system including estimation of the target surface emissivity. Furthermore, a roof-top shaped structure on top of the tile increases magnetic field incidence angles above 3 degrees. Laboratory tests of the system performed during its commissioning are presented. The global transmission of the optical system was found to be τ ≈ 40–50%. Poor spatial resolution compared to the design value was observed. Too large surface error of individual lenses was identified as the main cause and re-manufacturing of the most critical lens was suggested. First experimental results obtained using the IR system are presented: divertor heat flux profiles in L-mode with the heat flux decay length λ q omp = 2.1 − 3.3 mm and average H-mode heat flux profiles in an inter-ELM period and during an ELM heat flux maximum with λ q omp ≈ 0.6 mm and λ q omp ≈ 6.7 mm, respectively.

The microwave reflectometry system on COMPASS tokamak uses the frequency modulated continuous wave (FM-CW) in the K and Ka bands. The fast swept synthesizer together with the homodyne detection provides the complex beat frequency spectrum for the density profile reconstruction. The homodyne detection limits the use of reflectometry in the other applications like correlation or Doppler reflectometry. Our effort was to implement a heterodyne detection based on the existing system. We have decided to use a single-sideband modulator (SSBM) scheme to keep the compatibility with the fast sweeping. Lack of suitable SSBMs on the market leads us to use I/Q modulator, which is modulated by the in-quadrature signals.

A new fast infrared camera was purchased on the COMPASS tokamak recently. It is equipped with a medium wavelength infrared (3–5 mm) InSb detector and is capable of reaching framerate up to 1.9 kHz in full frame acquisition mode (320 × 256 px.) and up to 90 kHz in sub-windowed mode (64 × 4 px.). First experimental measurements of plasma heat flux to inner and outer wall limiters of the COMPASS tokamak using the new camera are presented. Time evolution of parallel heat flux during sawtooth instability is studied showing strong modulation of the heat flux absolute value whilst keeping constant its radial decay length. Fast modulation of outboard midplane limiter heat loading due to runaway electrons is also presented. The camera will be part of a new fast divertor thermographic system with exceptional spatial resolution (∼0.6–1.3 mm/px. on the target plane, 0.04–0.14 mm/px. mapped to the outer midplane) with a possibility of measurements of radial profiles on the divertor with 320 × 4 px. with temporal resolution better than 20 μs. A design of the foreseen optical divertor system is described together with a design of a special divertor graphite tile used for the IR thermography, that will allow in-situ surface emissivity calibration.

The COMPASS-U is a new tokamak in the design phase at Institute of Plasma Physics, Prague, Czech Republic. It is a medium-sized tokamak with high magnetic field (Bt = 5 T) and high temperature vessel ( This paper outlines the latest status on the design activities of the vacuum vessel concept and its mechanical verification against the electromagnetic forces. The vessel design concept is developed considering the spatial constraints, fabrication simplicity, minimum cost and the design is verified for minimum deformation and stresses in the vessel. It also includes the design evolution of PSP, PSP support and VV support. The mechanical analyses are carried out for load combinations of plasma transient events.

In this article the forward model and feasibility study of the CXRS (Charge Exchange Recombination Spectroscopy) diagnostic for the COMPASS Upgrade tokamak [1] based on the Raysect and Cherab framework [2] , [3] , [4] is presented. The neutral beam model available in Cherab is expanded and based on individual acceleration grid beamlets. The spatial density distribution calculation takes into account 3D geometry of the port structure. Beam density profile calculated with the expanded model is used to estimate realistic radial resolution of measurement and to produce forward models of the spectra. Effects of background plasma and beam halo are not included. The spectra are used to reconstruct the plasma profiles and are compared with the simulation input to estimate measurement errors with respect to positions of collecting optics.

The COMPASS-U tokamak is an advanced and more complicated successor of the COMPASS tokamak. Almost all main technological parts will be different. Both the higher performance of COMPASS-U and the increased number of parts and systems lead to a higher risk of failure. Therefore, new control systems must be developed regarding handling dangerous situations and integrating new systems. The COMPASS-U also opens the opportunity to make significant changes in the current systems based on the experience gained from COMPASS operation and to upgrade the systems to nowadays technologies. This article focuses on the conceptual design of the COMPASS-U control systems. It shows all CODAC (Control, Data Access, and Communication) systems their purpose, functionality, operation principle, interaction, and main used technologies. The COMPASS-U will use EPICS (Experimental Physics and Industrial Control System) for Slow control and supervision system. The real-time plasma control system will utilize MARTe2 (Multi-threaded Application Real-Time executor). The base control loop period of the Real-time plasma control system will be 50 μs as of COMPASS.

The COMPASS-U tokamak is designed at IPP CAS Prague. It will be a compact device that should achieve high toroidal magnetic field and high wall temperatures. In order to observe fast phenomena, photodiode arrays combined with beryllium filters and a pinhole are planned to be used as Soft X-Ray (SXR) detectors. Operational temperatures of photodiodes are typically below 100 °C and planned first wall temperatures as high as 500 °C for the later phases of operation. Therefore, an actively cooled support structure housing the detector has to be designed. Moreover, in order to obtain good inversion results the layout of tomographic diagnostics systems have to be optimised to provide the best possible coverage of the plasma. The proposed SXR system consists of two sets of detectors with different filter thickness enabling the use of the two filter method for electron temperature estimation. Both sets will share the same line of sight layout for better comparability. Optimisation of this layout is adapted for limited options of detector placement and extensive testing of tomography capabilities is performed. Results of these tests are shown for one of considered layouts.

The COMPASS-Upgrade tokamak, being designed as a medium-sized tokamak, operating with a hot first wall, allows for the study of DEMO-relevant plasma exhaust physics, crucial for future reactors. Bolometry diagnostics for COMPASS-U, consisting of metal foil bolometers and AXUV diodes, are proposed to measure spatially- and time-resolved radiation losses. Metal foil bolometers supply the absolute value of radiation power, whereas the AXUV diodes can observe fast phenomena such as MHD activity. Coverage of the whole poloidal cross-section by bolometers’ cameras allows tomography reconstruction of the local plasma emissivity. The metallic foil bolometry system will be based on sensors with a gold absorber on a silicon nitride substrate with a platinum resistor. Special modifications, e.g., channel separation, will be applied to the detectors to fulfil the requirements. Due to the high temperature, effective thermal shielding and cooling are essential to reduce the risk of damage to the detectors as well as reducing noise in the measured signal. The pin-hole cameras spatial configuration was optimized to provide the best performance under the given engineering constraints. The position of the cameras strongly depends on the space available behind the plasma-facing components (PFC). The proposed layout allows for an efficient observation of the confined plasma as well as that of the divertor region.

The effect of a minor concentration of energetic particles produced by parallel NB injection on Geodesic Acoustic Modes (GAM) spectrum is analyzed using fully kinetic equation. It is found that the GAM frequency is reduced by the effective mass renormalization due to that new energetic GAM appears with higher frequency. The electron current in combination with NB driven ion flow, modeled by shifted Maxwell distribution, may overcome the ion Landau damping thus resulting in the GAM instability when electron current velocity is larger than the effective parallel GAM phase velocity Rqω . Qualitative agreement of the theory with co/counter NB injection experiments in COMPASS tokamak is demonstrated.

Power handling experiments with a special liquid metal divertor module based on the capillary porous system technology were performed in the tokamak COMPASS. The performance of two metals (Li and LiSn alloy) were tested for the first time in a divertor under ELMy H-mode conditions. No damage of the capillary mesh and a good exhaust capability were observed for both metals in two separate experiments with up to 12 MW/m(2) of deposited perpendicular, inter-ELM steady-state heat flux and with ELMs of relative energy similar to 3% and a local peak energy fluence at the module similar to 15 kJ.m(-2). No droplets were directly ejected from the mesh top surface and for the LiSn experiment, no contamination of the core and SOL plasmas by Sn was observed. The elemental depth profile analysis of 14 stainless-steel samples located around the vacuum vessel for each experiment provides information about the migration of evaporated/redeposited liquid elements.

O-mode frequency-modulated continuous wave (FMCW) reflectometry provides an alternative to magnetic measurements in the determination of the plasma separatrix position for plasma position control. This type of measurement proves to be particularly attractive for the control of future fusion reactors where the harsh radiation environment may damage magnetic probes or induce non-compensable measurement drifts. Plasma position reflectometry (PPR), first demonstrated in ASDEX-Upgrade, is a control technique that is increasingly important to validate in diversified experimental devices and relevant plasma regimes. The COMPASS tokamak provides suitable conditions for such advanced demonstrations and regular PPR operation and development, thanks to its O-mode reflectometer and Multi-Threaded Application Real-Time executor (MARTe) based real-time control system. Herein we present the integration of a PPR system on COMPASS, both at hardware and software levels. Reflectometry swept measurements require signals to be acquired in bursts of data and streamed to the corresponding MARTe-PPR node through PCIe ® fibre-optic links. The data transferred in real-time is used to reconstruct the radial density profiles from which the outer separatrix position is estimated. This estimate is then delivered to the central MARTe controller node via a dedicated Xilinx ® Aurora ® link at a rate matching COMPASS's 500 μ s slow control cycle. The implemented system systematically met the required latency specifications, being able to deliver an estimation of the plasma radial position capable of successfully replacing the corresponding magnetic measurements in the plasma position feedback control loops.

The ITER first wall is designed for start-up and ramp-down in limiter configuration. The wall panels are toroidally shaped in order to spread the incident parallel power flux q|| uniformly, assuming a single decay length λq whose value is not known from first principles. In order to study the scaling of q|| with plasma parameters, infra-red viewing of specially-designed limiters has been used on the COMPASS tokamak in ∼100 discharges with scans in Ip, ne and for all combinations of magnetic field and Ip directions. The IR measurement clearly shows that in addition to the main SOL heat flux profile with λq > 40 mm, a steep gradient (λqnear = 4 ± 2 mm) dominates q|| near separatrix. This appears independently of limiter shaping, insertion with respect to neighbors and incident field-line angles. Good agreement is found between the measured λqnear and the prediction of a heuristic drift-based model.

The narrow scrape-off layer power component observed in COMPASS inner wall limiter circular discharges by means of IR thermography is investigated by Langmuir probes embedded in the limiter. The power flux profiles are in good agreement with IR observations and can be described by a double-exponential decay with a short decay length (

The Thomson scattering diagnostics (TS) at the COMPASS tokamak (operated in the Institute of Plasma Physics ASCR, Prague, Czech Republic) is based on two high-power Nd:YAG lasers, which have a pulse energy of 1.5 J and repetition rate of 30 Hz each. A new timing and synchronization unit (TSU) based on a Field Programmable Gate Array (FPGA) was designed and constructed in order to assure reliable and synchronized control of flash lamps and Q-switches of both lasers. Correct delay between laser pulses is necessary to obtain the highest possible laser energy and to prevent the active medium, the Nd:YAG rod, from thermal damage. An FPGA development kit was chosen as core hardware for the TSU and dedicated input and output circuits were manufactured to adapt the kit interfaces for COMPASS TS needs. In addition, the FPGA firmware, the control software, and the graphical user interface were developed to control the TSU hardware. This paper describes the TS regimes that are addressed by the new TSU. Further, the TSU design, the operation flow, and the firmware and software development are presented. Finally, the results of commissioning are shown.

The COMPASS plasma control system is based on the MARTe real-time framework. Thanks to MARTe modularity and flexibility new algorithms have been developed for plasma diagnostic (plasma position calculation), control (shaping field control), and protection systems (central solenoid protection). Moreover, the MARTe framework itself was modified to broaden the communication capabilities via Aurora. This paper presents the recent upgrades and improvements made to the COMPASS real-time plasma control system, focusing on the issues related to precision of the real-time calculations, and discussing the improvements in terms of discharge parameters and stability. In particular, the new real-time system has given the possibility to analyze and to minimize the transport delays of each control loop.

This paper presents an overview of the Control, Data Acquisition, and Communication system (CODAC) at the COMPASS tokamak: the hardware set-up, software implementation, and communication tools are described. The diagnostics and the data acquisition are tailored for high spatial and temporal resolution required by the COMPASS physics programme, which aims namely at studies of the plasma edge, pedestal, and Scrape-off-Layer (SOL). Studies of instabilities and turbulence are also an integral part of the programme. Therefore, the data acquisition consists of more than 1000 channels, sampled at rates from 500 kS/s up to 2 GS/s. Presently, the feedback system controls the plasma position and shape, plasma current, and density and it includes 32 analogue input channels as well as 1 digital input/output channel and 8 analogue outputs. The feedback control runs within the Multi-threaded Application Real-Time executor (MARTe) framework with two threads, a 500 μs cycle to control slow systems and a 50 μs cycle to control the fast feedback power supplies for plasma position control. In this paper, special attention is paid to the links between the systems, to the hardware and software connections, and to the communication. The hardware part is described, the software framework is addressed, and the particular implementation – the dedicated software modules, communication protocols, and links to the database are described.

The main magnetic fields in COMPASS – i.e. The Toroidal, Magnetising, Equilibrium, and Shaping Fields – are created by a set of four corresponding thyristor power supplies controlled in a 0.5 ms loop. The plasma position has to be controlled both radially and vertically by two additional magnetic fields provided by two fast amplifiers (FAs) based on MOSFET technology, each supplying ±100 V and up to ±5 kA. Currently, an ongoing project aims at ELM triggering by fast changes of the vertical position of the plasma column, also referred to as vertical kicks. For this purpose, a new Vertical Kicks Power Supply (VKPS) capable of quick change of vertical plasma position is being constructed. This power supply should operate at up to 1.2 kV with switching frequency up to 5 kHz. It is designed as a H-bridge but based on IGBT transistors which can be operated at higher voltages than MOSFETs. In this paper, we focus on the FAs and VKPS engineering design and required output parameters. Both the power supplies are based on modern components with highest available ratings in their categories. Unique design of the power supplies takes advantage of the short duration of the COMPASS discharge by overloading the transistors above their maximal steady-state rating. The FA is regularly operating, so that in addition to describing its design, we also describe the achieved performance parameters. Finally, the common controller unit, communication, and error handling is described.

The COMPASS tokamak is expected to produce several gigabytes of data per shot in near future. A new storage system is needed to accommodate and access all the data. It should be scalable, fault-tolerant, and parallel. It should not be based on proprietary solutions to maintain independence from hardware and software manufacturers and preferably it should be built on inexpensive commodity hardware. One of the promising distributed parallel fault-tolerant file systems, GlusterFS, was selected for testing. The aim of the work was to make initial tests of a particular small GlusterFS setup to confirm its aptitude for the COMPASS storage system. Aggregated reading throughput from multiple NFS clients was one of the most important figures that were benchmarked, it scaled well with the number of clients, starting just above 60 MiB/s 1 for 1 client and going slightly over 300 MiB/s for 6 clients.

The COMPASS tokamak, a divertor device with clear H-mode and ITER-relevant geometry, has been re-installed in IPP Prague after its transport from CCFE in UK. The first plasma was achieved in December 2008. Many new diagnostic tools with both high temporal and spatial resolutions have been developed to address the scientific programme of COMPASS focused on H-mode physics and pedestal investigations. In the paper, an overview of existing and in near future planned diagnostics (magnetic, spectroscopy, microwave, probe and beam/particle) on COMPASS is given including their basic technical specifications and achievements.

An efficient horizontal and vertical stabilization of the plasma column position are essential for a reliable tokamak operation. Plasma position is generally determined by plasma current, plasma pressure and external vertical and horizontal magnetic fields. Such fields are generated by poloidal field coils and proper algorithm for the current control have to by applied, namely, in case of fast feedback loops. This paper presents a real-time plasma position reconstruction algorithms developed for the COMPASS tokamak. Further, its implementation in the MARTe (Multithreaded Application Real-Time executor) is described and the first results from test of the algorithm for real-time control of horizontal plasma positions are presented.

The COMPASS tokamak has started its operation recently at the Institute of Plasma Physics AS CR in Prague, Czech Republic. An important issue of the operation is the interlock system, which secures the safety of the personnel. The personnel protection is based on a restricted access into the experimental hall during the tokamak operation. An experimental hall access system, based on Honeywell WIN-PAK™2005, allows to set the status of the experimental area and to control the movement of the personnel. A hardware interlock, based on a PLC MicroPEL M66, interprets the experimental hall status and controls the safety of the operation of key systems accordingly. The permit for operation is granted and the real status of the systems is reported by hard-wired potential-less contacts. The PLC provides a HW interface between Actuators (relays and switches) and it is connected on PESNET bus. Second site of personnel protection system is created on a PC where runs a .NET application on MS Windows XP. This PC is connected with PLC via PESNET bus (on RS485 layer) and it creates an operator interface. Details of the set-up are described in this contribution.

A new camera system ‘event detection intelligent camera’ (EDICAM) is being developed by the Hungarian Association and has been installed on the COMPASS tokamak in the Institute of Plasma Physics AS CR in Prague, during February 2009. The standalone system contains a data acquisition PC and a prototype sensor module of EDICAM. Appropriate optical system have been designed and adjusted for the local requirements, and a mechanical holder keeps the camera out of the magnetic field. The fast camera contains a monochrome CMOS sensor with advanced control features and spectral sensitivity in the visible range. A special web based control interface has been implemented using Java spring framework to provide the control features in a graphical user environment. Java native interface (JNI) is used to reach the driver functions and to collect the data stored by direct memory access (DMA). Using a built in real-time streaming server one can see the live video from the camera through any web browser in the intranet. The live video is distributed in a Motion Jpeg format using real-time streaming protocol (RTSP) and a Java applet have been written to show the movie on the client side. The control system contains basic image processing features and the 3D wireframe of the tokamak can be projected to the selected frames. A MatLab interface is also presented with advanced post processing and analysis features to make the raw data available for high level computing programs. In this contribution all the concepts of EDICAM control center and the functions of the distinct software modules are described.

Modern fusion experiments require the presence of several subsystems, responsible for the different parameters involved in the operation of the machine. With the migration from the pre-programmed to the real-time control paradigm, their integration in Control, Data Acquisition, and Communication (CODAC) systems became an important issue, as this implies not only the connection to a main central coordination system, but also communications with related diagnostics and actuators. A subsystem for the control and operation of the vacuum, gas injection and baking was developed and installed in the COMPASS tokamak. These tasks are performed by dsPIC microcontrollers that receive commands from a hub computer and send information regarding the status of the operation. Communications are done in the serial protocol RS-232 through fibre optics. Java software, with an intuitive graphical user interface, for controlling and monitoring of the subsystem was developed and installed in a hub computer. In order to allow operators to perform these tasks remotely besides locally, this was integrated in the FireSignal system. Taking advantage of FireSignal features, it was possible to provide the users with, not only the same functionalities of the local application but also a similar user interface. An independent FireSignal Java Node bridges the central server and the control application. This design makes possible to easily reuse the Node for other subsystems or integrate the vacuum slow control in the other CODAC systems. The complete system, with local and remote control, has been installed successfully on COMPASS and has been in operation since April this year.

The COMPASS tokamak has started its operation recently in Prague and to meet the necessary operation parameters its real-time system, for data processing and control, must be designed for both flexibility and performance, allowing the easy integration of code from several developers and to guarantee the desired time cycle. For this purpose an Advanced Telecommunications Computing Architecture based real-time system has been deployed with a solution built on a multi-core x86 processor. It makes use of two software components: the BaseLib2 and the MARTe (Multithreaded Application Real-Time executor) real-time frameworks. The BaseLib2 framework is a generic real-time library with optimized objects for the implementation of real-time algorithms. This allowed to build a library of modules that process the acquired data and execute control algorithms. MARTe executes these modules in kernel space Real-Time Application Interface allowing to attain the required cycle time and a jitter of less than 1.5 μs. MARTe configuration and data storage are accomplished through a Java hardware client that connects to the FireSignal control and data acquisition software. This article details the implementation of the real-time system for the COMPASS tokamak, in particular the organization of the control code, the design and implementation of the communications with the actuators and how MARTe integrates with the FireSignal software.

The COMPASS-D tokamak, originally operated in UKAEA Culham, UK, is being reinstalled in the Institute of Plasma Physics (IPP), AS CR. COMPASS-D was designed as a flexible tokamak in the 1980s mainly to explore MHD physics. Its operation (with D-shaped vessel) began in UKAEA in 1992. In 2001 COMPASS-D had been mothballed and later offered to the Institute of Plasma Physics (IPP Prague) AS CR. The re-installation of the COMPASS-D tokamak in IPP Prague had started in 2006. Due to the low power available from the local grid, the two flywheel-generators (47 MVA, 45 MJ, 85 Hz, 6.3 kV) are installed as storage of the required energy. Four AC/DC thyristor rectifiers provide the desired current profiles in toroidal and poloidal coil systems. The start-up circuit, which provides a loop voltage necessary for the plasma generation, is based on fully solid-state switchers and two temporarily inserted resistors. This paper describes the design of the new power supply system and shows details of the commissioning procedures and installation. We also present some results of a comprehensive analysis of the circuit operation performed in Matlab Simulink.

The Compass tokamak is currently being installed in Prague, Czech Republic. Its control and data acquisition system is being redesigned and built from scratch and it will be based on novel digital technologies. The proposed hardware for the controller is based on the PICMG 3.0 Advanced Telecommunications Computing Architecture ™ (ATCA) standard. The platform contains one ATCA controller with a Gigabit Ethernet interface, up to 12 ATCA Digitizer-Generator-Processor (DGP) cards and trigger and clock inputs, all on a 12U shelf. The multi-core × 86-based General Purpose Processor (GPP) controller will be connected to the DGP cards by Peripheral Component Interconnect Express ™ (PCIe) point-to-point links through the ATCA backplane. Multiple-input multiple-output (MIMO) signal processing will be shared by the DGP cards using the built-in Field Programmable Gate Arrays (FPGAs) and the controller’s × 86 general processor. Eleven Aurora ™ 2.5 Gbit/s links allow to further parallelize the execution of code among several FPGAs. In order to guarantee real-time execution of the control codes a framework based on Linux and the Real-Time Application Interface (RTAI) will be used. This will explore the features provided by the new multi-core technologies. Synchronization between the subsystems will be guaranteed by a real-time event network. The interface to the system will be provided by the FireSignal control and data acquisition system. This will allow the operators and diagnostic coordinators to configure the hardware, prepare the discharges, pre-program events of interest and follow results from the discharge. FireSignal will also orchestrate the data flow coming from the different diagnostics into the database and to registered data clients.

Control of fusion experiments requires non-ambiguous, easy to use, user-interfaces to configure hardware devices. With that aim, a highly generic system for data control and acquisition has been developed. Among the main features it allows remote hardware configuration, shot launching, data sharing between connected users and experiment monitoring. The system is fully distributed: the hardware driver nodes, clients and servers are completely independent from each other and might run in different operating systems and programmed in different languages. All the communication is provided through the Common Object Request Broker Architecture (CORBA) protocol. FireSignal is designed to be as independent as possible from any kind of constraints as it is a plugin based system. Database, data viewers and the security system are some examples of what can easily be changed and adapted to the target machine's needs. In this system, every hardware is described in eXtensible Markup Language (XML) and with this information Graphical User Interfaces (GUI) are automatically built and user's parameter configuration validated. Any type of hardware device can be integrated in the system as long as it is described in XML and the respective driver developed. Any modern programming language can be used to develop these drivers. Currently Python and Java generic drivers are used. Data storage and indexing is time stamp event-based. Nodes are responsible for tagging the acquired samples with the absolute time stamps and to react to machine events. FireSignal is currently being used to control the ISTTOK/PT and CASTOR/CZ tokamaks.

Each EURATOM Association stores data using proprietary schemes, usually developed by the research unit or using third party software. The temporary exchange of researchers between laboratories is a common practice nowadays. When the researchers returns to the home laboratory, there is usually the need to follow the work. The amount of available data is becoming enormous and the main data index is changing from shot number to time and events, where the pulse number is just one among the most relevant events against data is catalogued. These difficulties can be overcome by using a common software layer between end-users and laboratories. The components needed to create this software abstraction layer, between users and laboratories data, have already been developed using a universal and well known remote procedure call standard (RPC) based on the eXtensible Markup Language (XML): XML-RPC. The library allows data retrieval using the same methods for all associations. Users are authenticated through the PAPI system ( http://papi.rediris.es ), allowing each organization to use its own authentication schema. Presently there are libraries and server implementations in Java and C++. These libraries have been included and tested in some of the most common data analysis programs such as MatLab and IDL. The system is already being used in ISTTOK/PT and CASTOR/CZ.

The ion temperature is a particularly important but rarely measured plasma boundary quantity. In this work we introduce a new electric probe, the segmented tunnel probe (STP), which measures ion temperature, electron temperature, and parallel ion current density simultaneously and with high temporal resolution. The probe was built and tested in the CASTOR tokamak. The STP was operated in a Mach-probe arrangement in a DC mode, providing bi-directional measurements with the temporal resolution of 1 μs. Therefore, it has significant potential to be employed in the research of transient phenomena in tokamaks (e.g. turbulence, fluctuations and ELMs). We present radial profiles of the plasma parameters in the CASTOR tokamak measured by the STP, using calibrations from particle-in-cell simulations.

Near-sonic parallel flows are systematically observed in the far scrape-off layer (SOL) of the limiter tokamak Tore Supra, as in many L-mode X-point divertor tokamak plasmas. The poloidal variation of the parallel flow has been measured by moving the contact point of a small circular plasma onto limiters at different poloidal angles. The resulting variations of flow are consistent with the existence of a poloidally localized enhancement of radial transport concentrated in a 30° sector near the outboard midplane. If the plasma contact point is placed on the inboard limiters, then the SOL expands to fill all the space between the plasma and the outboard limiters, with density decay lengths between 10 and 20 cm. On the other hand, if the contact point lies on the outboard limiters, the localized plasma outflux is scraped off and the SOL is very thin with decay lengths around 2–3 cm. The outboard radial transport would have to be about two orders of magnitude stronger than inboard to explain these results.

A study of the non-equilibrium absorption of hydrogen particles by a plasma-facing absorption probe (AP) made of Group V metals in the CASTOR tokamak environment has been undertaken with the main purposes: (1) to investigate the role of nonmetallic coatings upon plasma-facing materials in D/T inventory and recycling and (2) to develop a method of the registration and diagnostic of the flux of suprathermal hydrogen. Two series of experiments were performed: with AP of Nb and of V. The absorption of suprathermal hydrogen particles coming from the tokamak plasma was investigated as a function of AP temperature, AP distance from the plasma, AP bias and of plasma pulse duration. The possibility of a reliable registration of suprathermal hydrogen was demonstrated in spite of the short plasma pulse duration and a relatively high background H2 pressure. The composition of the hydrogen flux (molecules, atoms, ions) impinging on the tokamak walls was analyzed, including ion energy distribution.

The response of the scrape-off layer (SOL) to supersonic pulsed gas injection (SPGI) in Tore Supra is measured by a reciprocating Mach probe. The edge density increases abruptly following injection and decays to its pre-injection value in about 10 ms. The edge temperature falls to 5–10 eV range. The perturbation appears to be toroidally symmetric. The density increase depends on the injected amount of deuterium gas, but the temperature decrease does not. The parallel Mach number changes during the density spike; the sign of the change depends on the poloidal location of the injection nozzle. We use a simple one-dimensional fluid model for the SOL to interpret the measurements. The Mach number change lasts about 10 ms as well, indicating the existence of a poloidally localized ionization source in the vicinity of the nozzle.

The structure of the naturally occurring velocity shear layer and the dynamical coupling between gradients and transport have been investigated in the JET plasma boundary region. The velocity shear layer appears to organize itself to reach a condition in which the radial gradient in the poloidal phase velocity of fluctuations is comparable to the inverse of the correlation time of fluctuations (1/tau). This result suggests that E x B sheared flows organized themselves to be close to marginal stability (i.e. omega(ExB) approximate to 1/tau). The size of turbulent events increases when the plasma deviates from the average gradient. The resulting radial velocity of fluctuations is of the order of 20 m/s for transport events implying a small deviation from the most probable gradient. This value is consistent with a diffusive modeling with B2-Eirene. The radial velocity increases up to 500 m/s for large transport events. (C) 2003 Elsevier Science B.V. All rights reserved.