H. Fernandes

University of Lisbon, Lisboa, Lisbon, Portugal

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Publications (132)104.78 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: The ISTTOK tokamak was upgraded with a plasma control system based on the Advanced Telecommunications Computing Architecture (ATCA) standard. This control system was designed to improve the discharge stability and to extend the operational space to the alternate plasma current (AC) discharges as part of the ISTTOK scientific program. In order to accomplish these objectives all ISTTOK diagnostics and actuators relevant for real-time operation were integrated in the control system. The control system was programmed in C++ over the Multi-threaded Application Real-Time executor (MARTe) which provides, among other features, a real-time scheduler, an interrupt handler, an intercommunications interface between code blocks and a clearly bounded interface with the external devices. As a complement to the MARTe framework, the BaseLib2 library provides the foundations for the data, code introspection and also a Hypertext Transfer Protocol (HTTP) server service. Taking advantage of the modular nature of MARTe, the algorithms of each diagnostic data processing, discharge timing, context switch, control and actuators output reference generation, run on well-defined blocks of code named Generic Application Module (GAM). This approach allows reusability of the code, simplified simulation, replacement or editing without changing the remaining GAMs. The ISTTOK control system GAMs run sequentially each 100 μs cycle on an Intel® Q8200 4-core processor running at 2.33 GHz located in the ATCA crate. Two boards (inside the ATCA crate) with 32 analog-to-digital converters (ADCs) were used for acquiring the diagnostics data. Each ADC operates at 2 Msample/s but (for real-time operation) the acquired data is decimated in real-time on the board's Field-programmable gate array (FPGA) to a frequency defined by the control cycle time. This paper presents the ISTTOK real-time architecture and the human–machine Interface (HMI) for simplified AC discharge programming.
    Fusion Engineering and Design. 01/2014;
  • Contributions to Plasma Physics 11/2013; 53(9):615-622. · 0.93 Impact Factor
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    ABSTRACT: e-lab is a remote laboratory infrastructure that provides access to several distinct experiments that may be performed independently. A new experiment to be introduced in this remote laboratory is our first geographically distributed experiment: the World Pendulum. It consists in multiple identical pendulum apparatuses connected to e-lab and scattered throughout different locations across several countries. The World Pendulum is intended at exploring a unique feature allowed by remote experimentation — experimental repetition in different locations. This demonstration aims at presenting the e-lab interface and its main features as well as exploring the new World Wide distributed Pendulum experiment.
    Experiment@ International Conference (exp.at'13), 2013 2nd; 01/2013
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    ABSTRACT: The main objective of this work is to report on the measurements of in-depth profiles for the hydrogen retained in liquid gallium samples exposed to ISTTOK tokamak plasmas. Several samples were exposed to a large number of ISTTOK discharges varying the total exposure time (1, 3 and 10 s) to study saturation effects in retention. The sample hydrogen content was evaluated by means of ion beam analysis (ERDA and RBS). The analysis has shown evidences of saturation as the increase in hydrogen content from 3 to 10 s exposures is five times lower than for the 1 to 3 s samples. On the other hand XPS analysis show different behavior for surface and in-depth retention since a large fraction of the measured hydrogen is retained in the form of hydrocarbons and hydroxides on the sample surface region.
    Journal of Nuclear Materials 01/2013; 438:S992–S995. · 1.21 Impact Factor
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    ABSTRACT: Pure tungsten and tantalum plates and tungsten-tantalum composites produced via mechanical alloying and spark plasma sintering were bombarded with He+ and D+ energetic ion beams and deuterium plasmas. The aim of this experiment is to study the effects caused by individual helium and deuterium exposures and to evidence that the modifications induced in the composites at different irradiation energies could be followed by irradiating the pristine constituent elements under the same experimental conditions, which is relevant considering the development of tailored composites for fusion applications. Higher D retentions, especially in tungsten, and superficial blistering are observed in both components after helium exposure. The blistering is magnified in the tantalum phase of composites due to its higher ductility and to water vapour production under deuterium irradiation. At lower irradiation energies the induced effects are minor. After plasma exposure, the presence of tantalum does not increase the D content in the composites.
    Journal of Nuclear Materials 01/2013; · 1.21 Impact Factor
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    Materials Science Forum 01/2013; 730:925-930.
  • Conference Proceeding: World Pendulum @ e-lab
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    ABSTRACT: World Pendulum is a project with the main purpose of studying the behavior of standard gravity with latitude. Several automated simple pendulums are distributed across different latitudes. Each of these pendulums can be remotely operated over the Internet, communicating in real time the measured period of the oscillations, which may then be used to calculate the value of g. This article describes the World Pendulum project and it's implementation integrated into e-lab, a software framework that allows remote control of real experiments over the Internet[1]. Preliminary results show that a good agreement with the established spherical harmonics model is obtained, with the absolute overall error being under 0.0002 m/s2.
    Experiment@ International Conference (exp.at'13), 2013 2nd; 01/2013
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    ABSTRACT: The tokamak ISTTOK havy ion beam diagnostic (HIBD) operates with a multiple cell array detector (MCAD) that allows for the plasma density and the plasma density fluctuations measurements simultaneously at different sampling volumes across the plasma. To improve the capability of the plasma density fluctuations investigations, a new detection system and new signal conditioning amplifier have been designed and tested. The improvements in MCAD design are presented which allow for nearly complete suppression of the spurious plasma background signal by applying a biasing potential onto special electrodes incorporated into MCAD. The new low cost and small size transimpedance amplifiers are described with the parameters of 400 kHz, 10(7) V∕A, 0.4 nA of RMS noise, adequate for the plasma density fluctuations measurements.
    The Review of scientific instruments 10/2012; 83(10):10D705. · 1.52 Impact Factor
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    ABSTRACT: A diagnostic technique based on the Cherenkov effect is proposed for detection and characterization of fast (super-thermal and runaway) electrons in fusion devices. The detectors of Cherenkov radiation have been specially designed for measurements in the ISTTOK tokamak. Properties of several materials have been studied to determine the most appropriate one to be used as a radiator of Cherenkov emission in the detector. This technique has enabled the detection of energetic electrons (70 keV and higher) and the determination of their spatial and temporal variations in the ISTTOK discharges. Measurement of hard x-ray emission has also been carried out in experiments for validation of the measuring capabilities of the Cherenkov-type detector and a high correlation was found between the data of both diagnostics. A reasonable agreement was found between experimental data and the results of numerical modeling of the runaway electron generation in ISTTOK.
    The Review of scientific instruments 08/2012; 83(8):083505. · 1.52 Impact Factor
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    ABSTRACT: A pinhole probe (PHP) for the simultaneous measurement of the parallel, T(parallel), and perpendicular, T(perpendicular), ion temperature has been designed and tested in the scrape-off-layer (SOL) plasma of the tokamak ISTTOK. The PHP consists of a tunnel immersed into the plasma parallel to magnetic field and an ion collector. One end of the tunnel is covered with a thin foil that has a pinhole sampling ions from the plasma. The other end of the tunnel (close to the negatively biased collector) is covered with a fine-mesh screen. The possibility of performing an analytical description of the PHP current-to-voltage characteristics obtained on the collector when biasing the tunnel simplifies the interpretation of the results. The PHP operation has been previously tested in T(parallel), T(perpendicular) measurements in low temperature weekly magnetized plasma [H. Mase, T. Honzava, and G. Miyamoto, J. Appl. Phys. 49(10), 5171 (1978)]. In this paper, the PHP operation in the SOL of the tokamak ISTTOK is described, and the first results of T(parallel) and T(perpendicular) measurements are presented. The obtained results demonstrate strong (~30%) variation of T(parallel) and T(perpendicular) on a time scale of 0.5 ms, and general predominance of T(parallel) > T(perpendicular) anisotropy (T(parallel mean)/T(perpendicular mean) ~ 1.5) during plasma shot.
    The Review of scientific instruments 03/2012; 83(3):033505. · 1.52 Impact Factor
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    ABSTRACT: In a tokamak, the accurate estimation of the plasma boundary is essential to maximise the fusion performance and is also the first line of defence for the physical integrity of the device. In particular, the first wall components might get severely damaged if over-exposed to a high plasma thermal load. The most common approach to calculate the plasma geometry and related parameters is based in a large set of different types of magnetic sensors. Using this information, real-time plasma equilibrium codes infer a flux map and calculate the shape and geometry of the plasma boundary and its distance to a known reference (e.g. first wall). These are inputs to one or more controllers capable of acting on the shape and trajectory based in pre-defined requests. Depending on the device, the error of the estimated boundary distance must usually be less than 1 centimetre, which translates into very small errors on the magnetic measurement itself. Moreover, asymmetries in the plasma generated and surrounding magnetic fields can produce local shape deformations potentially leading to an unstable control of the plasma geometry. The JET tokamak was recently upgraded to a new and less thermally robust all-metal wall, also known as the ITER-like wall. Currently the shape controller system uses the output of a single reconstruction algorithm to drive the plasma geometry and the protection systems have no input from the plasma boundary reconstruction. These choices are historical and were due to architectural, hardware and processing power limitations. Taking advantage of new multi-core systems and of the already proved robustness of the JET real-time network, this paper proposes a distributed architecture for the real-time identification of faults in the magnetic measurements of the JET tokamak. Besides detecting simple faults, such as short-circuits and open-loops, the system compares the expected measurement at the coil location and the real measurement, producing a confidence valu- . Several magnetic reconstructions, using sensors from multiple toroidally distributed locations, can run in parallel, allowing for a voting or averaging scheme selection. Finally, any fault warnings can be directly fed to the real-time protection sequencer system, whose main function is to coordinate the protection of the JET's first wall.
    Real Time Conference (RT), 2012 18th IEEE-NPSS; 01/2012
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    ABSTRACT: The Vertical Stabilization system of the JET tokamak has been recently upgraded. This new system enables a more sensitive control of the plasma geometry and can withstand larger perturbations, enabling scientists to push the plasma performance to its limits without risking a severe control loss, which might endanger the machine integrity. The project was successfully delivered in the course of 2010. This paper briefly introduces the new JET Vertical Stabilization design, discussing how its modular architecture enabled the system to provide different experimental features in several operational environments. Furthermore, some of the major achievements of the commissioning activity and of the regular operation during the last experimental campaign are presented.
    Control Engineering Practice 01/2012; 20(9):846 - 856. · 1.67 Impact Factor
  • R.B. Neto, H. Fernandes, J. Pereira, A.S. Duarte
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    ABSTRACT: e-lab is a remote laboratory infrastructure, powered by a specific software framework, that allows to perform experiments and retrieve data from a remote apparatus. The deployment of new experiments on this platform is a complex and demanding process and an integrated overview for it is missing. An overview of e-lab's specifications is presented taking into account software development requirements for the deployment of new experimental apparatus and possible improvements.
    Remote Engineering and Virtual Instrumentation (REV), 2012 9th International Conference on; 01/2012
  • C Silva, P Duarte, H Fernandes, H Figueiredo
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    ABSTRACT: The interplay between mean and fluctuating E × B shear flows has been investigated in the ISTTOK edge plasma. The GAM shearing rate was found to be lower (by a factor of 2–3) than that of the mean flow but comparable to the turbulence decorrelation rate. A competition between GAMs and intermittent-like turbulent transport is observed leading to a dynamic view of plasma transport. External plasma biasing was found to modify the fluctuating shear flow. Negative bias induces a significant increase in the mean E × B shear flows, reducing turbulence and consequently suppressing the GAMs. On the other hand, an increase in the long-range correlation is observed for positive bias associated with a modest increase in the mean shear flow that might be interpreted as an enhanced energy transfer from the turbulence into large-scale, zonal flow-like structures.
    Plasma Physics and Controlled Fusion 01/2012; 54(8). · 2.37 Impact Factor
  • R.B. Neto, H. Fernandes, J. Pereira, A.S. Duarte
    [show abstract] [hide abstract]
    ABSTRACT: E-lab is a remote laboratory infrastructure, powered by a specific software framework, that allows to perform experiments and retrieve data from a remote apparatus. The deployment of new experiments on this platform is a complex and demanding process and an integrated overview for it is missing. An overview of e-lab's specifications is presented taking into account software development requirements for the deployment of new experimental apparatus and possible improvements.
    Remote Engineering and Virtual Instrumentation (REV), 2012 9th International Conference on; 01/2012
  • IX CICECO Meeting; 01/2012
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    ABSTRACT: The Multithreaded Application Real-Time executor (MARTe) software provides an environment for the hard real-time execution of codes while leveraging a standardized algorithm development process. The Experimental Physics and Industrial Control System (EPICS) software allows the deployment and remote monitoring of networked control systems. Channel Access (CA) is the protocol that enables the communication between EPICS distributed components. It allows to set and monitor process variables across the network belonging to different systems. The COntrol and Data Acquisition and Communication (CODAC) system for the ITER Tokamak will be EPICS based and will be used to monitor and live configure the plant controllers. The reconfiguration capability in a hard real-time system requires strict latencies from the request to the actuation and it is a key element in the design of the distributed control algorithm. Presently, MARTe and its objects are configured using a well-defined structured language. After each configuration, all objects are destroyed and the system rebuilt, following the strong hard real-time rule that a real-time system in online mode must behave in a strictly deterministic fashion. This paper presents the design and considerations to use MARTe as a plant controller and enable it to be EPICS monitorable and configurable without disturbing the execution at any time, in particular during a plasma discharge. The solutions designed for this will be presented and discussed.
    IEEE Transactions on Nuclear Science 09/2011; · 1.22 Impact Factor
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    ABSTRACT: A real-time plasma position control system is mandatory to achieve long duration (up to 250 ms), Alternating Current (AC) discharges on the ISTTOK tokamak. Such a system has been used for some time supported only on magnetic field diagnostic data. However, this system is clearly challenged when the plasma current is low, rendering it inoperative during the plasma current reversal. A tomography diagnostic with 3 pinhole cameras and 8 silicon photodiode channels per camera was installed and customized to supply alternative plasma position to be used for plasma position control. As no filtering is applied most of the radiation detected is in the visible/near-UV range. The data acquisition and control system is based on a 2MSPS, 32 channel acquisition ATCA module and the data processing is performed on a GPU that is connected to another ATCA module via the PCI-Express port for fast data access. Control commands are relayed to the plasma positioning PF power supplies via optical serial ports. In this work, an overview of some of the tomographic reconstruction algorithms most commonly used for tokamak plasmas is done and an assessment is made on the best candidate for the proposed real-time implementation. The tomography acquisition and plasma control systems operating at ISTTOK are also described. This system aims at achieving the following goals: (i) execute a tomographic reconstruction; (ii) determine the average emissivity position from it; (iii) calculate the shift from the axis and (iv) supply the vertical field power supply with the desired current value, all in less than 100 μs. The horizontal magnetic field power supply unit, essential for vertical plasma positioning, is foreseen to be integrated in the system and will have no impact in the processing time.
    IEEE Transactions on Nuclear Science 09/2011; · 1.22 Impact Factor
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    ABSTRACT: The ISTTOK boundary plasma velocity near the outer midplane is measured on the parallel and perpendicular directions in four different configurations by reversing independently the toroidal magnetic field and the plasma current directions. The parallel flow is found to not depend significantly on both the toroidal magnetic field and plasma current directions, being always directed towards the nearest limiter in the scrape-off layer. On the contrary, the perpendicular flow is found to follow the Er × B drift direction. The poloidal velocity has also been derived from the correlation of floating potential signals measured on poloidally separated probes and a good agreement with the value derived with the Gundestrup probe is found. Finally, the dynamical interplay between parallel momentum and turbulent particle flux has been investigated and a clear dynamical coupling between these quantities is found in the region inside the limiter.
    Journal of Nuclear Materials 08/2011; 415(1):S433–S436. · 1.21 Impact Factor
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    ABSTRACT: The retarding field analyzer (RFA) is a widely used diagnostic tool for the ion temperature measurement in the scrape-off-layer (SOL) of the thermonuclear plasma devices. However, the temporal resolution in the standard RFA application is restricted to the ms timescale. In this paper, a dc operation of the RFA is considered, which allows for the measurement of the plasma ion temperature fluctuations. The method is based on the relation for the RFA current-voltage (I-V) characteristic resulted from a common RFA model of shifted Maxwellian distribution of the analyzed ions, and the measurements of two points on the exponentially decaying region of the I-V characteristic with two differently dc biased RFA electrodes. The method has been tested and compared with conventional RFA measurements of the ion temperature in the tokamak ISTTOK SOL plasma. An ion temperature of T(i) = 17 eV is obtained near the limiter position. The agreement between the results of the two methods is within ∼25%. The amplitude of the ion temperature fluctuations is found to be around 5 eV at this location. The method has been validated by taking into account the effect of fluctuations in the plasma potential and the noise contamination, proving the reliability of the results obtained. Finally, constrains to the method application are discussed that include a negligible electron emission from the RFA grids and the restriction to operate in the exponentially decaying region of the I-V characteristic.
    The Review of scientific instruments 04/2011; 82(4):043505. · 1.52 Impact Factor

Publication Stats

148 Citations
357 Downloads
104.78 Total Impact Points

Institutions

  • 2013
    • University of Lisbon
      Lisboa, Lisbon, Portugal
  • 2010–2013
    • Technical University of Lisbon
      • Institute for Plasma Research and Nuclear Fusion (IPFN)
      Lisboa, Lisbon, Portugal
    • University of Aveiro
      Aveiro, Aveiro, Portugal
  • 1993–2011
    • Instituto Técnico y Cultural
      Santa Clara de Portugal, Michoacán, Mexico
  • 1999–2008
    • Instituto Superior de Contabilidade e Administração de Lisboa
      Lisboa, Lisbon, Portugal