J. Zebrowski

National Centre for Nuclear Research, Warszawa, Masovian Voivodeship, Poland

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Publications (34)19.55 Total impact

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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 Note reports on experimental studies of ripple born fast electrons within the TORE-SUPRA facility, which were performed by means of a modified measuring head equipped with diamond detectors designed especially for recording the electron-induced Cherenkov radiation. There are presented signals produced by fast electrons in the TORE-SUPRA machine, which were recorded during two experimental campaigns performed in 2010. Shapes of these electron-induced signals are considerably different from those observed during the first measurements carried out by the prototype Cherenkov probe in 2008. An explanation of the observed differences is given.
    The Review of scientific instruments 01/2013; 84(1):016107. · 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 diagnostics capable of characterizing the runaway and superthermal electrons has been developing on the ISTTOK tokamak. In previous paper, a use of single-channel Cherenkov-type detector with titanium filter for runaway electron studies in ISTTOK was reported. To measure fast electron populations with different energies, a prototype of a four-channel detector with molybdenum filters was designed. Test-stand studies of filters with different thicknesses (1, 3, 7, 10, 20, 50, and 100 μm) have shown that they should allow the detection of electrons with energies higher than 69, 75, 87, 95, 120, 181, and 260 keV, respectively. First results of measurements with the four-channel detector revealed the possibility to measure reliably different fast electrons populations simultaneously.
    The Review of scientific instruments 10/2010; 81(10):10D304. · 1.52 Impact Factor
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    ABSTRACT: The paper describes experimental studies of electron beams emitted from a plasma torus within the ISTTOK tokamak, which were performed by means of a new four-channel detector of the Cherenkov type. A range of electron energy was estimated. There were also measured hard X-rays, and their correlation with the fast run-away electron beams was investigated experimentally.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2010; 623(2):686-689. · 1.14 Impact Factor
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    ABSTRACT: The paper presents a schematic design and tests of a system applicable for measurements of fast electron pulses emitted from high-temperature plasma generated inside magnetic confinement fusion machines, and particularly in the TORE-SUPRA facility. The diagnostic system based on the registration of the Cherenkov radiation induced by fast electrons within selected solid radiators is considered, and electron low-energy thresholds for different radiators are given. There are some estimates of high thermal loads, which might be deposited by intense electron beams upon parts of the diagnostic equipment within the TORE-SUPRA device. There are some proposed measures to overcome this difficulty by the selection of appropriate absorption filters and Cherenkov radiators, and particularly by the application of a fast-moving reciprocating probe. The paper describes the measuring system, its tests, as well as some results of the preliminary measurements of fast electrons within TORE-SUPRA facility.
    The Review of scientific instruments 01/2010; 81(1):013504. · 1.52 Impact Factor
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    ABSTRACT: The paper concerns detectors of the Cherenkov radiation which can be used to measure high-energy electrons escaping from short-living plasma. Such detectors have high temporal (about 1 ns) and spatial (about 1 mm) resolution. The paper describes a Cherenkov-type detector which was designed, manufactured and installed in the ISTTOK tokamak in order to measure fast runaway electrons. The radiator of that detector was made of an aluminium nitride (AlN) tablet with a light-tight filter on its front surface. Cherenkov signals from the radiator were transmitted through an optical cable to a fast photomultiplier. It made possible to perform direct measurements of the runaway electrons of energy above 80 keV. The measured energy values and spatial characteristics of the recorded electrons appeared to be consistent with results of numerical modelling of the runaway electron generation process in the ISTTOK tokamak.
    Radiation Measurements - RADIAT MEAS. 01/2010; 45(9):1014-1019.
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    ABSTRACT: The paper presents an improved version of a miniature mass-spectrometer of the Thomson-type, which has been adopted for ion analysis near the dense plasma region inside a vacuum chamber. Problems connected with the separation of ions from plasma streams are considered. Input diaphragms and pumping systems, needed to ensure good vacuum inside the analyzing region, are described. The application of the miniature Thomson-type analyzer is illustrated by ion parabolas recorded in plasma-focus facility and rod plasma injector experiment. A quantitative analysis of the recorded ion parabolas is presented. Factors influencing accuracy of the ion analysis are discussed and methods of the spectrometer calibration are described.
    The Review of scientific instruments 06/2009; 80(5):053504. · 1.52 Impact Factor
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    ABSTRACT: The paper describes the application of SSNTDs of the PM-355 type to diagnostics of reaction products emitted from high-temperature deuterium plasmas produced in Plasma Focus (PF) facilities. Acceleration processes occurring in plasma lead often to the generation of high-energy ion beams. Such beams induce nuclear reactions and contribute to the emission of fast neutrons, fusion protons and alpha particles from PF discharges with a deuterium gas. Ion measurements are of primary importance for understanding the mechanisms of the physical processes which drive the charged-particle acceleration. The main aim of the present studies was to perform measurements of spatial- and energy-distributions of fusion-reaction protons (about 3MeV) within a PF facility. Results obtained from energy measurements were compared with the proton-energy spectra computed theoretically. The protons were measured by means of a set of ion pinhole cameras equipped with PM-355 detectors, which were placed at different angles relative to the electrode axis of the PF facility.
    Radiation Measurements - RADIAT MEAS. 01/2009; 44(9):878-880.
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    ABSTRACT: Summary form only given. Measurements of the energetic particles (electrons and ions) are one of the main scientific tasks for various experimental devices generating high-temperature plasmas. The significance of such studies is proportional to the amount of information about different processes occurring inside plasma, in which such charged particles are involved. For measurements of fast electrons in tokamaks there were developed special Cherenkov-type probes of high spatial- and temporal-resolution. The applicability of the Cherenkov detectors for measurements of fast electrons in high-current plasma discharges has been studied theoretically and experimentally, with particular attention to their capabilities. In all cases the practical application of such detectors requires the selection of appropriate radiators and consideration of geometrical- and thermal-limitations. On the basis of our previous studies the Cherenkov-type detectors have been designed and adapted for the direct observation of fast (runaway) electrons in small-size tokamaks. During experiments with the ISTTOK facility discharges with low plasma currents (3-4 kA) were studied and runaway electrons of energies > 80 keV were successfully recorded. The electron measurements, as performed at different radial positions of the detector head, demonstrated a distinct increase in the radiation signal when the probe approached the bulk plasma. An analysis of the experimental results revealed good agreement between the obtained data and theory of runaway processes. This paper reports on the most important results of the experiment and its analysis.
    IEEE International Conference on Plasma Science 01/2009;
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    ABSTRACT: Gas, fluid, or solid Cherenkov-type detectors have been widely used in high-energy physics for determination of parameters of charged particles, which are moving with relativistic velocities. This paper presents experimental results on the detection of runaway electrons using Cherenkov-type detectors in the ISTTOK tokamak discharges. Such detectors have been specially designed for measurements of energetic electrons in tokamak plasma. The technique based on the use of the Cherenkov-type detectors has enabled the detection of energetic electrons (energies higher than 80 keV ) and determination of their spatial and temporal parameters in the ISTTOK discharges. Obtained experimental data were found in adequate agreement to the results of numerical modeling of the runaway electron generation in ISTTOK.
    Review of Scientific Instruments 11/2008; · 1.60 Impact Factor
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    ABSTRACT: The paper reports on capabilities of an improved version of the Cherenkov detector designed for measurements of fast electrons. The described technique enables the identification of electron beams, the measurements of their temporal characteristics, as well as the estimation of their spatial properties to be performed. Results obtained in the last experimental campaign with the CASTOR facility show good measuring capabilities of such a detection system. The radial distributions of fast-electron streams at different plasma densities, as well as the electron fluency dependences on discharge currents and toroidal magnetic fields are also presented.
    AIP Conference Proceedings. 04/2008; 996(1).
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    ABSTRACT: The paper reports on experimental studies performed within the CASTOR tokamak, which was operated at IPP in Prague, Czech Republic, during the last experimental campaign carried out in autumn 2006. The main aim was to implement a new diagnostic technique for measurements of energetic (>80 keV) electrons within the tokamak edge plasma region. The technique was based on the use of a Cherenkov-type probe similar to the first prototype detector, which was tested during the previous experiments with the CASTOR device. In particular, the distributions of fast electrons in a standard scenario at different values of plasma current Ip, and toroidal magnetic field BT are determined.
    AIP Conference Proceedings. 03/2008; 993(1):255-258.
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    ABSTRACT: The paper describes results of the recent measurements of fusion-reaction protons, which were performed within the PF-360 facility operated at the IPJ in Swierk, Poland. The main aim of those studies was to perform time-integrated measurements of fast protons (of energy of about 3 MeV) by means of ion-pinhole cameras, which were equipped with solid state nuclear track detectors (SSNTD) of the PM-355 type and absorption filters made of thin metal foils. In order to determine the spatial distribution of fusion-produced protons the use was made of several miniature pinhole cameras placed at different angles to the PF-360 axis. The irradiated and etched detectors were analyzed with an optical microscope coupled with a CCD camera and a PC unit.
    03/2008;
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    ABSTRACT: The paper describes applications of solid-state nuclear track detectors (SSNTDs) of the PM-355 type for diagnostics of fusion-reaction protons emitted from high-temperature deuterium plasmas. The results of our calibration studies of SSNTDs and fusion-proton measurements, carried out within two plasma-focus facilities (PF-360 and PF-1000), are presented. The main aim of those studies was to perform time-integrated measurements of 3MeV fusion-reaction protons by means of ion-pinhole cameras equipped with the PM-355 detectors, placed at different angles relative to the axis of PF-360 and PF-1000 facilities.
    Radiation Measurements - RADIAT MEAS. 01/2008; 43.
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    ABSTRACT: This paper concerns various applications of powerful ion- and plasma-streams generated by high-current pulse discharges realized within different plasma-focus (PF) facilities. General characteristics of the emitted plasma-ion streams are summarized. The possibility of application of special arrangements, e.g. cryogenic targets, CD2 or metal wires, hydrogen or deuterium getters, special alloy targets, etc, is described. The paper presents results of different experiments oriented on the interaction of the pulsed plasma-ion streams with various material targets placed inside PF-360 device (at IPJ in Swierk) and PF-1000 facility (at IPPLM in Warsaw). Attention is paid to plasma–target interactions and influence of the material targets on emission characteristics of the PF-type discharges. The diagnostics includes current and voltage measurements, optical photography and spectroscopy, x-ray emission observations and fast-neutron measurements (from deuterium discharges). Particular attention is paid to time-resolved spectroscopic studies. The use of pulsed ion- and plasma-streams for modifications of different materials, e.g. those of particular interest for the construction of nuclear fusion reactors, is described.
    Physica Scripta 03/2006; 2006(T123):66. · 1.03 Impact Factor
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    ABSTRACT: The paper reports on measurements of fusion reaction protons, which were emitted from high-current Plasma Focus discharges. The experiments were carried out on two Plasma Focus facilities (PF-360 and PF-1000) and the obtained results are compared in the paper. The paper presents some detailed maps of the fusion proton fluxes, which were recorded with the pinhole cameras. These maps show distributions and shapes of fast proton sources within the pinch plasma column.
    01/2006;
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    ABSTRACT: The paper concerns a novel diagnostic technique applicable for indirect, spatially resolved measurements of energetic electrons generated inside tokamak-type facilities. Such measurements can be performed making use of the Cherenkov-effect induced by fast electrons inside a transparent medium (radiator). A construction of the Cherenkov-type detectors adapted for tokamak research is presented and preliminary results of the first measurements carried out within the CASTOR tokamak operated at IPP in Prague are reviewed.
    Czechoslovak Journal of Physics 01/2006; 56:B98-B103. · 0.42 Impact Factor
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    ABSTRACT: This invited talk describes spectroscopic studies of high-current plasma discharges within PF- and RPI-type facilities, used for basic and application-oriented research. Particular attention is paid to measurements of temporal changes of spectral lines from working gases and impurities. Time-resolved spectral measurements were carried out by means of a Mechelle(R)900 spectrometer, operating in the wavelength range from about 200 nm to 1100 nm, with exposition times varied from 100 ns up to 50 ms. That spectrometer was equipped with a cooled CCD camera coupled with a PC and GRAMS-32(R) software. Spectroscopic studies of the deuterium Balmer-lines and some impurity lines, as observed within the PF-360 experiment, are presented and discussed. Estimates of temporal changes in the electron concentration and temperature are given. Measurements of temporal changes in the emission of the deuterium- and impurity-lines emitted from a mega-joule PF-1000 facility are also described. Capabilities of optical techniques to study the interaction of PF discharges with different targets are discussed. Time-resolved spectroscopic studies of plasma discharges within the RPI-IBIS facility, used for material engineering, are also presented. Optical spectra, as recorded for different operational modes, are compared. The use of spectroscopic techniques to study the interaction of pulsed plasma-ion streams with different materials is considered. The presented results of research on dynamics of pulsed plasma streams (produced in different experimental facilities) as well as the described optical diagnostic techniques are important not only for basic physical studies but also for application-oriented research.
    Proc SPIE 09/2005;
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    ABSTRACT: The paper reports on recent studies of plasma-focus (PF) discharge dynamics and fusion neutron emission, which were performed with the PF-360 device at the energy level of about 120 kJ and the maximum current of 1.85 MA. Using the high-speed multi-frame imaging system, the behavior of a current-sheath layer during the radial compression phase and of a plasma column during the pinch phase has been investigated. Dynamics of the pinch phase was studied in the visible radiation and soft X-rays simultaneously. Characteristics of the neutron emission from PF discharges, which were carried out with and without the use of planar D2O-ice target, were studied experimentally. In particular, the anisotropy coefficient, defined as a ratio of the fusion-neutron yield to that measured at 90 to the z-axis, i.e. Y n()/Y n (90), was investigated under different experimental conditions. Various structures of the time-resolved neutron signals were recorded and interpreted, e.g. as a result of a double pinch. Possible mechanisms of the fusion neutron production have also been discussed.
    Czechoslovak Journal of Physics 05/2004; 54(6):643-659. · 0.42 Impact Factor