H. Fernandes

Instituto Técnico y Cultural, Santa Clara de Portugal, Michoacán, Mexico

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Publications (146)124.41 Total impact

  • C Silva, J Adamek, H Fernandes, H Figueiredo
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    ABSTRACT: In this work, the fluctuations properties measured by Langmuir and ball-pen probes are compared, aiming at investigating the influence of temperature fluctuations on Langmuir probe measurements, including the cross-field turbulent particle flux. With this aim, a 5-pin probe was designed to estimate the radial particle transport due to fluctuations simultaneously using Langmuir and ball-pen probes. A considerable difference is observed in the amplitude of the floating potential fluctuations measured by the two types of probes, but not in statistical properties such as skewness. The turbulent particle flux was found to be roughly four times larger when measured with Langmuir probes. However, quantities such as the phase velocity of the fluctuations or the poloidal correlation lengths are not significantly different, as floating potential fluctuations measured by both types of probes are highly correlated and roughly in phase. Finally, it is suggested that ball-pen and emissive probes may underestimate the amplitude of the plasma potential fluctuations and therefore probe measurements must be carefully validated.
    Plasma Physics and Controlled Fusion 02/2015; 57(2). · 2.37 Impact Factor
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    ABSTRACT: The paper describes an influence of a Cherenkov-type probe, which is used for measurements of fast electron streams inside the ISTTOK chamber, on other probes and behaviour of a plasma ring. The reported study shows that such a probe situated near the plasma column has a strong influence on signals from another Cherenkov probe, and can cause a considerable reduction of electron-induced signals. This effect does not depend on positions of the probes in relation to the limiter. Measurements of hard X-ray (HXR) emission show that the deeply immersed Cherenkov probe can also influence on the limiter . Under specific experimental conditions such a Cherenkov probe can play the role of a new limiter and change the plasma configuration.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 12/2014; 767:61–66. · 1.14 Impact Factor
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    ABSTRACT: The Heavy Ion Beam Diagnostic (HIBD) on the tokamak ISTTOK (Instituto Superior Técnico TOKamak) has been modified, in terms of signal conditioning, to measure the local fluctuations of the neσ1,2(Te) product (plasma density times the effective ionization cross-section) along the tokamak minor diameter, in 12 sample volumes in the range of -0.7a < r < 0.7a, with a maximum delay time of 1 μs. The corresponding signals show high correlation with the magnetic Mirnov coils in the characteristic MHD frequency range of ISTTOK plasmas and enable the identification of tearing modes. This paper describes the HIBD signal conditioning system and presents a preliminary analysis of the radial profile measurements of local neσ1,2(Te) fluctuations.
    Review of Scientific Instruments 10/2014; 85(11). · 1.60 Impact Factor
  • I.S. Nedzelskiy, C. Silva, H. Fernandes
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    ABSTRACT: Measurements of the ion temperature fluctuations by retarding field energy analyzed (RFA) based on two point measurements on the exponentially decaying region of the I-V characteristic with two differently DC biased RFA electrodes have been tested and proved in the experiments on the tokamak ISTTOK. In this paper, a DC operation of an RFA has been applied to give direct instantaneous measurements of the electron temperature and electron temperature fluctuations. The results are in good agreement with conventional swept measurements from the RFA. The observed electron temperature fluctuations, 3 mm outside the leading edge of the limiter, have a typical normalized amplitude (standard deviation divided by the average value) of ∼13% (Teav = 6 eV) and are in opposition to the fluctuations of the floating potential simultaneously measured on the RFA slit.
    Review of Scientific Instruments 09/2014; 85(9):093506-093506-5. · 1.60 Impact Factor
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    ABSTRACT: The paperdescribesaninfluence ofaCherenkov-typeprobe,whichisusedformeasurementsoffast electron streamsinsidetheISTTOKchamber,onotherprobesandbehaviourofaplasmaring.The reportedstudyshowsthatsuchaprobesituatedneartheplasmacolumnhasastronginfluence on signals fromanotherCherenkovprobe,andcancauseaconsiderablereductionofelectron-induced signals. Thiseffectdoesnotdependonpositionsoftheprobesinrelationtothelimiter.Measurementsof hard X-ray(HXR)emissionshowthatthedeeplyimmersedCherenkovprobecanalsoinfluence onthe limiter .Underspecific experimentalconditionssuchaCherenkovprobecanplaytheroleofanew limiter andchangetheplasmaconfiguration.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 08/2014; Vol. 767:61-66. · 1.14 Impact Factor
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    ABSTRACT: The first derivative probe technique was applied to study the ISTTOK tokamak plasma. This technique employs the electron part of the Langmuir probe current-voltage (IV) characteristic and yields information on the plasma potential and the electron energy distribution function (EEDF). The IV characteristic was measured with new electrical probes mounted on a horizontal manipulator, one oriented in parallel and the other perpendicularly to the magnetic field lines. Using the first-derivative probe technique, the plasma potential and the EEDF at different radial positions were acquired. We show that, in the vicinity of the last close flux surface (LCFS), the EEDF is non-Maxwellian and can be approximated by a bi-Maxwellian one with a dominant cold electron population and a minority group of hot electrons. In the limiter shadow, the EEDF obtained is Maxwellian.
    Journal of Physics Conference Series 05/2014; 514(1):012050.
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    ABSTRACT: The ISTTOK tokamak has a long tradition on alternate plasma current (AC) discharges, but the old control system was limiting and lacked full system integration. In order to improve the AC discharges performance the ISTTOK fast control system was updated. This control system developed on site based on the Advanced Telecommunications Computing Architecture (ATCA) standard now integrates the information gathered by all the tokamak real-time diagnostics to produce an accurate observation of the plasma parameters. The real-time actuators were also integrated, allowing a Multiple Input Multiple Output (MIMO) control environment with several synchronization strategies available. The control system software was developed in C++ on top of a Linux system with the Multi-threaded Application Real-Time executor (MARTe) Framework to synchronize the real-time code execution under a 100μs control cycle. In addition, to simplify the discharge programming, a visual Human–Machine Interface (HMI) was also developed using the BaseLib2 libraries included in the MARTe Framework. This paper presents the ISTTOK control system and the optimizations that extended the AC current discharges duration to more than 1 s, corresponding to 40 semi-cycles without apparent degradation of the plasma parameters. This upgrade allows ISTTOK to be used as a low-cost material testing facility with long time exposures to nuclear fusion relevant plasmas, comparable (in duration) with medium size tokamaks.
    Fusion Engineering and Design 04/2014; · 0.84 Impact Factor
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    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 03/2014; · 0.84 Impact Factor
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    ABSTRACT: A remotely controlled automated apparatus is used to accurately test linear momentum conservation at low friction conditions. Electronic control of the magnetic actuators and photoelectric acquisition system is performed by a dsPIC30 microcontroller, connected to the e-lab platform. Placed at a high school, this experiment aims to encourage electronics and physics learning at a pre-college level and demonstrate e-lab's scouting potential.
    11th International Conference on Remote Engineering and Virtual Instrumentation 2014 (REV); 01/2014
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    ABSTRACT: The paper reports on experimental studies of electron beams in the ISTTOK tokamak, those were performed by means of an improved four-channel detector. The Cherenkov-type detector measuring head was equipped with four radiators made of two types of alumina-nitrate (AlN) poly-crystals: machinable and translucent ones, both of 10 mm in diameter and 2.5 mm in thickness. The movable support that enabled the whole detectors to be placed inside the tokamak vacuum chamber, at chosen positions along the ISTTOK minor radius. Since the electron energy distribution is one of the most important characteristics of tokamak plasmas, the main aim of the study was to perform estimations of an energy spectrum of the recorded electrons. For this purpose the radiators were coated with molybdenum (Mo) layers of different thickness. The technique based on the use of Cherenkov-type detectors enabled the detection of fast electrons (of energy above 66 keV) and determination of their spatial and temporal characteristics in the ISTTOK experiment. Measurements of hard X-rays (HXR), which were emitted during ISTTOK discharges, have also been performed. Particular attention was paid to the correlation measurements of HXR pulses with run-away electron beams. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    Contributions to Plasma Physics 11/2013; 53(9):615-622. · 0.93 Impact Factor
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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 07/2013; 438:S992–S995. · 2.02 Impact Factor
  • Conference Paper: 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: 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; · 2.02 Impact Factor
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    Materials Science Forum 01/2013; 730:925-930.
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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 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

Publication Stats

407 Citations
124.41 Total Impact Points

Institutions

  • 1993–2014
    • Instituto Técnico y Cultural
      Santa Clara de Portugal, Michoacán, Mexico
  • 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
  • 1999–2008
    • Instituto Superior de Contabilidade e Administração de Lisboa
      Lisboa, Lisbon, Portugal