H. Fernandes

MARTe: A Multiplatform Real-Time Framework

Development of real-time applications is usually associated with nonportable code targeted at specific real-time operating systems. The boundary between hardware drivers, system services, and user code is commonly not well defined, making the development in the target host significantly difficult. The Multithreaded Application Real-Time executor (MARTe) is a framework built over a multiplatform library that allows the execution of the same code in different operating systems. The framework provides the high-level interfaces with hardware, external configuration programs, and user interfaces, assuring at the same time hard real-time performances. End-users of the framework are required to define and implement algorithms inside a well-defined block of software, named Generic Application Module (GAM), that is executed by the real-time scheduler. Each GAM is reconfigurable with a set of predefined configuration meta-parameters and interchanges information using a set of data pipes that are provided as inputs and required as output. Using these connections, different GAMs can be chained either in series or parallel. GAMs can be developed and debugged in a non-real-time system and, only once the robustness of the code and correctness of the algorithm are verified, deployed to the real-time system. The software also supplies a large set of utilities that greatly ease the interaction and debugging of a running system. Among the most useful are a highly efficient real-time logger, HTTP introspection of real-time objects, and HTTP remote configuration. MARTe is currently being used to successfully drive the plasma vertical stabilization controller on the largest magnetic confinement fusion device in the world, with a control loop cycle of 50 ?s and a jitter under 1 ?s. In this particular project, MARTe is used with the Real-Time Application Interface (RTAI)/Linux operating system exploiting the new ?86 multicore processors technology.

Integrated scenario in JET using real-time profile control

The recent development of real-time measurements and control tools in JET has enhanced the reliability and reproducibility of the relevant ITER scenarios. Diagnostics such as charge exchange, interfero-polarimetry, electron cyclotron emission have been upgraded for real-time measurements. In addition, real-time processes like magnetic equilibrium and q profile reconstruction have been developed and applied successfully in real-time q profile control experiments using model based control techniques. Plasma operation and control against magnetohydrodynamic instabilities are also benefiting from these new systems. The experience gained at JET in the field of real-time measurement and control experiments operation constitutes a very useful basis for the future operation of ITER scenarios.

Engineering aspects of the tokamak ISTTOK

AbstractThe first Portuguese magnetic confinement experiment, the tokamak ISTTOK, has been in operation since 1993. This tokamak device is described and the main technological features, as well as the novel techniques of its diagnostics and control and data acquisition system, are reported. A synopsis of the experimental activity is also presented.

Enhancement of the ISTTOK plasma confinement and stability by negative limiter biasing

Experimental results concerning the plasma response to the biasing of the tokamak ISTTOK localized limiters, on a strong flat-top plasma current reference discharge, are reported. Modifications of central beta as well as of energy confinement time are determined through time-resolved measurements of the line-averaged plasma density, electron density profile, electron temperature and ohmic power. Gross particle confinement variations are confirmed by the associated changes of the ratio between the line-averaged electron density and the radiation level. Plasma stability modifications are analysed by measurements of the plasma column transverse displacement, plasma poloidal rotation frequency and sliding fast Fourier transform spectra of both the magnetic and the electron density fluctuations. The evolution of the amplitude as well as the frequency of the most important tearing modes is determined. Negative bias leads to better particle and energy confinement, and improved stability. Positive bias reduces both confinement and stability, causing a significant transitory vertical displacement of the plasma column as well as of its current axis.

Generation of sheared poloidal flows via Reynolds stress and transport barrier physics

A view of the latest experimental results and progress in the understanding of the role of poloidal flows driven by fluctuations via Reynolds stress is given. Reynolds stress shows a radial gradient close to the velocity shear layer location in tokamaks and stellarators, indicating that this mechanism may drive significant poloidal flows in the plasma boundary. Observation of the generation of E×B sheared flows via Reynolds stress at the ion Bernstein resonance layer has been noticed in toroidal magnetized plasmas. The experimental evidence of sheared E×B flows linked to the location of rational surfaces in stellarator plasmas might be interpreted in terms of Reynolds stress sheared driven flows. These results show that E×B sheared flows driven by fluctuations can play an important role in the generation of transport barriers.

A fully computerized and distributed VME system for control and data acquisition on the tokamak ISTTOK

Abstract The ISTTOK operation and research programme require a very reliable control and data acquisition system due to the pulsed nature of the tokamak discharges. This system (SCAD) was designed in a distributed, modular, multivendor, integrated and transparent approach, taking advantage of recent improvements in networking, front-end processing and database management. This paper reports some of the most relevant aspects involved in the design of the SCAD current configuration. The computer system is based on personal computers (PCs) and Motorola 68 000 family microprocessors, linked by an ethernet local area network. Control is made by a vacuum controller unit as well as by VME digital I/O, timing and digital-to-analog converter modules. Data acquisition is provided by VME instrumentation as well as by PC based modules and by a digitizing oscilloscope. All VME modules were developed on site. The ISTTOK operation is controlled by a supervisory program. Data from the engineering and physics diagnostics is stored in a central database.

Operation of the tokamak ISTOKK in a multicycle alternating flat-top plasma current regime

Operation of the tokamak ISTTOK in a multicycle alternating square wave plasma current regime is reported. Discharges with seven half-cycles without dwell times, over a total time span of about five times the maximum duration of a single DC discharge, were obtained by feeding the primary of the transformer with an electrolytic capacitor bank switched in polarity by a fast insulated gate bipolar transistor (IGBT) H bridge

Characterization of geodesic acoustic modes in the ISTTOK edge plasma

ISTTOK is equipped with two probe systems that allow the simultaneous measurement of the three-dimensional characteristics of the edge fluctuations with high temporal resolution. Electrostatic fluctuations consistent with the geodesic acoustic mode (GAM) are observed in the edge plasma. The radial, poloidal and toroidal structure of the fluctuations are investigated and good agreement with the GAM theoretical predictions is found. Furthermore, experimental evidence is presented suggesting that the GAM is modulating long-range correlations and the ambient turbulent fluctuations.

Compact retarding field energy analyzer for the tokamak ISTTOK boundary plasma

The retarding field energy analyzer (RFEA) remains the more reliable diagnostic to measure the ion temperature in the boundary plasmas of magnetic fusion devices. A compact, simple design and inexpensive RFEA has been developed for investigations on the tokamak ISTTOK. It consists of a stainless steel pinhole (with a diameter of 0.6mm), three fine nickel grids with a separation of 1mm, and a collector, all insulated by mica. All the components are placed inside a boron nitride housing with dimensions of 14×14×23mm3. The RFEA has been tested in both ion and electron modes. The conditions of the RFEA operation are discussed, and preliminary measurements of the ion and electron temperature profiles presented.

Edge plasma pressure measurements using a mechanical force sensor on the tokamak ISTTOK

In the present paper we report on a novel mechanical probe, which is able to measure the plasma pressure directly. The probe consists of two pendulums whose heads are exposed to the tokamak edge plasma, while the deflection is measured very sensitively outside the plasma by means of semi-conductor strain gauges. The plasma pressure was successfully measured in the ISTTOK edge plasma, its value being in good agreement with that derived from the electrical probe data (pp = 1–10 Pa). Furthermore, we discuss the possibility of determining the ion temperature Ti = pp/n − Te by combining the pressure measurement with those of n and Te from the electrical probes. Although the derived ion temperatures—besides that in the region close to the limiter—were reasonable, its uncertainty is still very large.