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Détails du magazine
Format
Magazine
eISSN
1508-5791
Première publication
25 Mar 2014
Période de publication
4 fois par an
Langues
Anglais

Chercher

Volume 60 (2015): Edition 2 (June 2015)

Détails du magazine
Format
Magazine
eISSN
1508-5791
Première publication
25 Mar 2014
Période de publication
4 fois par an
Langues
Anglais

Chercher

31 Articles
Accès libre

Generation of shock waves in dense plasmas by high-intensity laser pulses

Publié en ligne: 22 Jun 2015
Pages: 193 - 198

Résumé

Abstract

When intense short-pulse laser beams (I > 1022 W/m2, τ < 20 ps) interact with high density plasmas, strong shock waves are launched. These shock waves may be generated by a range of processes, and the relative significance of the various mechanisms driving the formation of these shock waves is not well understood. It is challenging to obtain experimental data on shock waves near the focus of such intense laser–plasma interactions. The hydrodynamics of such interactions is, however, of great importance to fast ignition based inertial confinement fusion schemes as it places limits upon the time available for depositing energy in the compressed fuel, and thereby directly affects the laser requirements. In this manuscript we present the results of magnetohydrodynamic simulations showing the formation of shock waves under such conditions, driven by the j × B force and the thermal pressure gradient (where j is the current density and B the magnetic field strength). The time it takes for shock waves to form is evaluated over a wide range of material and current densities. It is shown that the formation of intense relativistic electron current driven shock waves and other related hydrodynamic phenomena may be expected over time scales of relevance to intense laser–plasma experiments and the fast ignition approach to inertial confinement fusion. A newly emerging technique for studying such interactions is also discussed. This approach is based upon Doppler spectroscopy and offers promise for investigating early time shock wave hydrodynamics launched by intense laser pulses.

Mots clés

  • shock waves
  • radiation hydrodynamics
  • laser–plasma interactions
  • fast ignition
  • inertial confinement fusion
  • Doppler spectroscopy
Accès libre

Selected methods of electron-and ion-diagnostics in tokamak scrape-off-layer

Publié en ligne: 22 Jun 2015
Pages: 199 - 206

Résumé

Abstract

This invited paper considers reasons why exact measurements of fast electron and ion losses in tokamaks, and particularly i n a scrape-off-layer and near a divertor region, are necessary in order to master nuclear fusion energy production. Attention is also paid to direct measurements of escaping fusion products from D-D and D-T reactions, and in particular of fast alphas which might be used for plasma heating. The second part describes the generation of so-called runaway and ripple-born electrons which might induce high energy losses and cause severe damages of internal walls in fusion facilities. Advantages and disadvantages of different diagnostic methods applied for studies of such fast electrons are discussed. Particular attention is paid to development of a direct measuring technique based on the Cherenkov effect which might be induced by fast electrons in appropriate radiators. There are presented various versions of Cherenkov-type probes which have been developed by the NCBJ team and applied in different tokamak experiments. The third part is devoted to direct measurements of fast ions (including those produced by the nuclear fusion reactions) which can escape from a high-temperature plasma region. Investigation of fast fusion-produced protons from tokamak discharges is reported. New ion probes, which were developed by the NCBJ team, are also presented. For the first time there is given a detailed description of an ion pinhole camera, which enables irradiation of several nuclear track detectors during a single tokamak discharge, and a miniature Thomson-type mass-spectrometer, which can be used for ion measurements at plasma borders.

Mots clés

  • diagnostics
  • electrons
  • ions
  • fusion products
  • probes
  • tokamak
Accès libre

Ion acceleration from intense laser-generated plasma: methods, diagnostics and possible applications

Publié en ligne: 22 Jun 2015
Pages: 207 - 212

Résumé

Abstract

Many parameters of non-equilibrium plasma generated by high intensity and fast lasers depend on the pulse intensity and the laser wavelength. In conditions favourable for the target normal sheath acceleration (TNSA) regime the ion acceleration from the rear side of the target can be enhanced by increasing the thin foil absorbance through the use of nanoparticles and nanostructures promoting the surface plasmon resonance effect. In conditions favourable for the backward plasma acceleration (BPA) regime, when thick targets are used, a special role is played by the laser focal position with respect to the target surface, a proper choice of which may result in induced self-focusing effects and non-linear acceleration enhancement. SiC detectors employed in the time-of-flight (TOF) configuration and a Thomson parabola spectrometer permit on-line diagnostics of the ion streams emitted at high kinetic energies. The target composition and geometry, apart from the laser parameters and to the irradiation conditions, allow further control of the plasma characteristics and can be varied by using advanced targets to reach the maximum ion acceleration. Measurements using advanced targets with enhanced the laser absorption effect in thin films are presented. Applications of accelerated ions in the field of ion source, hadrontherapy and nuclear physics are discussed.

Mots clés

  • ion acceleration in plasma
  • plasma diagnostics
  • TOF
  • target normal sheath acceleration (TNSA)
Accès libre

Shock dynamics induced by double-spot laser irradiation of layered targets

Publié en ligne: 22 Jun 2015
Pages: 213 - 219

Résumé

Abstract

We studied the interaction of a double-spot laser beam with targets using the Prague Asterix Laser System (PALS) iodine laser working at 0.44 μm wavelength and intensity of about 1015 W/cm2. Shock breakout signals were recorder using time-resolved self-emission from target rear side of irradiated targets. We compared the behavior of pure Al targets and of targets with a foam layer on the laser side. Results have been simulated using hydrodynamic numerical codes.

Mots clés

  • laser shock
  • high pressures
  • non-uniformity smoothing
Accès libre

The source of X-rays and high-charged ions based on moderate power vacuum discharge with laser triggering

Publié en ligne: 22 Jun 2015
Pages: 221 - 227

Résumé

Abstract

The source of X-ray radiation with the energy of quanta that may vary in the range hν = 1÷12 keV was developed for studies in X-ray interaction with matter and modification of solid surfaces. It was based on a vacuum spark discharge with the laser triggering. It was shown in our experiments that there is a possibility to adjust X-ray radiation spectrum by changing the configuration of the electrode system when the energy stored in the capacitor is varied within the range of 1÷17 J. A comprehensive study of X-ray imaging and quanta energy was carried out. These experiments were carried out for the case of both direct and reverse polarity of the voltage on the electrodes. Additionally, ion composition of plasma created in a laser-triggered vacuum discharge was analyzed. Highly charged ions Zn(+21), Cu(+20) and Fe(+18) were observed.

Mots clés

  • laser-triggered vacuum discharge
  • sources of X-rays
  • ion composition of plasma
Accès libre

Numerical simulations of generation of high-energy ion beams driven by a petawatt femtosecond laser

Publié en ligne: 22 Jun 2015
Pages: 229 - 232

Résumé

Abstract

This contribution presents results of a Particle-in-Cell simulation of ion beam acceleration via the interaction of a petawatt 25 fs laser pulse of high intensity (up to ~1021 W/cm2) with thin hydrocarbon (CH) and erbium hydride (ErH3) targets of equal areal mass density (of 0.6 g/m2). A special attention is paid to the effect that the laser pulse polarization and the material composition of the target have on the maximum ion energies and the number of high energy (>10 MeV) protons. It is shown that both the mean and the maximum ion energies are higher for the linear polarization than for the circular one. A comparison of the maximum proton energies and the total number of protons generated from the CH and ErH3 targets using a linearly polarized beam is presented. For the ErH3 targets the maximum proton energies are higher and they reach 50 MeV for the laser pulse intensity of 1021 W/cm2. The number of protons with energies higher than 10 MeV is an order of magnitude higher for the ErH3 targets than that for the CH targets.

Mots clés

  • laser acceleration
  • laser plasma
  • ions
  • particle-in-cell simulations
Accès libre

Hot electron refluxing in the short intense laser pulse interactions with solid targets and its influence on K-α radiation

Publié en ligne: 22 Jun 2015
Pages: 233 - 237

Résumé

Abstract

Fast electrons created as a result of the laser beam interaction with a solid target penetrate into the target material and initialize processes leading to the generation of the characteristic X-ray K-α radiation. Due to the strong electric field induced at the rear side of a thin target the transmitted electrons are redirected back into the target. These refluxing electrons increase the K-α radiation yield, as well as the duration of the X-ray pulse and the size of the radiation emitting area. A model describing the electron refluxing was verified via particle-in-cell simulations for non-relativistic electron energies. Using this model it was confirmed that the effect of the electron refluxing on the generated X-ray radiation depends on the target thickness and the target material. A considarable increase of the number of the emitted K-α photons is observed especially for thin targets made of low-Z materials, and for higher hot electron temperatures.

Mots clés

  • electron recirculation
  • electron refluxing
  • K-α radiation
  • laser–plasma interactions
  • particle-in-cell simulation
Accès libre

Electromagnetic pulses produced by expanding laser-produced Au plasma

Publié en ligne: 22 Jun 2015
Pages: 239 - 243

Résumé

Abstract

The interaction of an intense laser pulse with a solid target produces large number of fast free electrons. This emission gives rise to two distinct sources of the electromagnetic pulse (EMP): the pulsed return current through the holder of the target and the outflow of electrons into the vacuum. A relation between the characteristics of laser-produced plasma, the target return current and the EMP emission are presented in the case of a massive Au target irradiated with the intensity of up to 3 × 1016 W/cm2. The emission of the EMP was recorded using a 12 cm diameter Moebius loop antennas, and the target return current was measured using a new type of inductive target probe (T-probe). The simultaneous use of the inductive target probe and the Moebius loop antenna represents a new useful way of diagnosing the laser–matter interaction, which was employed to distinguish between laser-generated ion sources driven by low and high contrast laser pulses.

Mots clés

  • laser-produced plasma
  • electromagnetic pulse (EMP)
  • return target current
  • Moebius loop antenna
  • inductive target probe
Accès libre

High Power Laser Laboratory at the Institute of Plasma Physics and Laser Microfusion: equipment and preliminary research

Publié en ligne: 22 Jun 2015
Pages: 245 - 248

Résumé

Abstract

The purpose of this paper is to present the newly-opened High Power Laser Laboratory (HPLL) at the Institute of Plasma Physics and Laser Microfusion (IPPLM). This article describes the laser, the main laboratory accessories and the diagnostic instruments. We also present preliminary results of the first experiment on ion and X-ray generation from laser-produced plasma that has been already performed at the HPLL.

Mots clés

  • femtosecond pulses
  • high-power laser
  • inertial confinement fusion
  • laser plasma
Accès libre

First dedicated observations of runaway electrons in the COMPASS tokamak

Publié en ligne: 22 Jun 2015
Pages: 249 - 255

Résumé

Abstract

Runaway electrons present an important part of the present efforts in nuclear fusion research with respect to the potential damage of the in-vessel components. The COMPASS tokamak a suitable tool for the studies of runaway electrons, due to its relatively low vacuum safety constraints, high experimental flexibility and the possibility of reaching the H-mode D-shaped plasmas. In this work, results from the first experimental COMPASS campaign dedicated to runaway electrons are presented and discussed in preliminary way. In particular, the first observation of synchrotron radiation and rather interesting raw magnetic data are shown.

Mots clés

  • plasma diagnostics
  • runaway electrons
  • tokamak
Accès libre

Liquid micro pulsed plasma thruster

Publié en ligne: 22 Jun 2015
Pages: 257 - 261

Résumé

Abstract

A new type of pulsed plasma thruster (PPT) for small satellite propulsion is investigated, of which the most innovative aspect is the use of a non-volatile liquid propellant. The thruster is based on an open capillary design. The thruster achieved a thrust-to-power ratio above 45 μN/W, which constitutes a 5-fold improvement over the water-propelled pulsed plasma thruster, and which is also slightly above the performance of a similarly sized PPT with a solid propellant.

Mots clés

  • electric propulsion
  • pulsed plasma thruster
  • liquid propellant
Accès libre

Second order reflection from crystals used in soft X-ray spectroscopy

Publié en ligne: 22 Jun 2015
Pages: 263 - 265

Résumé

Abstract

In this note the ratio of the second to the first order reflection is determined for the KAP and PbSt crystals, for wavelengths corresponding to the Al K-line emission. The source of the radiation was a low-voltage stabilized X-ray tube. The X-rays were detected with a Bragg spectrometer equipped with a proportional counter detector. The signal measured by the proportional counter was subsequently pulse height analyzed.

Mots clés

  • soft X-ray
  • plasma spectroscopy
  • PbSt
  • KAP
Accès libre

Overview of processing technologies for tungsten-steel composites and FGMs for fusion applications

Publié en ligne: 22 Jun 2015
Pages: 267 - 273

Résumé

Abstract

Tungsten is a prime candidate material for the plasma-facing components in future fusion devices, e.g. ITER and DEMO. Because of the harsh and complex loading conditions and the differences in material properties, joining of the tungsten armor to the underlying construction and/or cooling parts is a complicated issue. To alleviate the thermal stresses at the joint, a sharp interface may be replaced by a gradual one with a smoothly varying composition. In this paper, several techniques for the formation of tungsten-steel composites and graded layers are reviewed. These include plasma spraying, laser cladding, hot pressing and spark plasma sintering. Structure, composition and selected thermal and mechanical properties of representative layers produced by each of these techniques are presented. A summary of advantages and disadvantages of the techniques and an assessment of their suitability for the production of plasma-facing components is provided.

Mots clés

  • plasma-facing components
  • functionally graded materials (FGMs)
  • tungsten
  • steel
  • plasma spraying
  • powder metallurgy
Accès libre

Heat load and deuterium plasma effects on SPS and WSP tungsten

Publié en ligne: 22 Jun 2015
Pages: 275 - 283

Résumé

Abstract

Tungsten is a prime choice for armor material in future nuclear fusion devices. For the realization of fusion, it is necessary to address issues related to the plasma–armor interactions. In this work, several types of tungsten material were studied, i.e. tungsten prepared by spark plasma sintering (SPS) and by water stabilized plasma spraying (WSP) technique. An intended surface porosity was created in the samples to model hydrogen/helium bubbles. The samples were subjected to a laser heat loading and a radiation loading of deuterium plasma to simulate edge plasma conditions of a nuclear fusion device (power density of 108 W/cm2 and 107 W/cm2, respectively, in the pulse intervals up to 200 ns). Thermally induced changes in the morphology and the damage to the studied surfaces are described. Possible consequences for the fusion device operation are pointed out.

Mots clés

  • tungsten
  • fusion
  • heat loading
  • irradiation
  • bubbles
  • surface damage
Accès libre

R&D on divertor plasma facing components at the Institute for Plasma Research

Publié en ligne: 22 Jun 2015
Pages: 285 - 288

Résumé

Abstract

This paper is focused on various aspects of the development and testing of water cooled divertor PFCs. Divertor PFCs are mainly designed to absorb the heat and particle fluxes outflowing from the core plasma of fusion devices like ITER. The Divertor and First Wall Technology Development Division at the Institute for Plasma Research (IPR), India, is extensively working on development and testing of divertor plasma facing components (PFCs). Tungsten and graphite macro-brush type test mock-ups were produced using vacuum brazing furnace technique and tungsten monoblock type of test mock-ups were obtained by hot radial pressing (HRP) technique. Heat transfer performance of the developed test mock-ups was tested using high heat flux tests with different heat load conditions as well as the surface temperature monitoring using transient infrared thermography technique. Recently we have established the High Heat Flux Test Facility (HHFTF) at IPR with an electron gun EH300V (M/s Von Ardenne Anlagentechnik GmbH, Germany) having maximum power 200 kW. Two tungsten monoblock type test mock-ups were probed using HHFTF. Both of the test mock-ups successfully sustained 316 thermal cycles during high heat flux (HHF) tests. The test mock-ups were non-destructively tested using infrared thermography before and after the HHF tests. In this note we describe the detailed procedure used for testing macro-brush and monoblock type test mock-ups using in-house transient infrared thermography set-up. An acceptance criteria limit was defined for small scale macro-brush type of mock-ups using DTrefmax value and the surface temperature measured during the HHF tests. It is concluded that the heat transfer behavior of a plasma facing component was checked by the HHF tests followed by transient IR thermography. The acceptance criteria DTrefmax limit for a graphite macro-brush mock-up was found to be ~3°C while for a tungsten macro-brush mock-up it was ~5°C.

Mots clés

  • divertor
  • plasma facing material
  • high heat flux test
  • transient IR thermography
Accès libre

Change of silica luminescence due to fast hydrogen ion bombardment

Publié en ligne: 22 Jun 2015
Pages: 289 - 292

Résumé

Abstract

This paper deals with the luminescence of silica (KV-type) induced by beam of hydrogen ions with the energy of 210 keV per nucleon. An average implantation dose of up to 3.5 × 1021 cm−3 (5 × 1010 Gy) was accumulated during irradiation over an extended period. The luminescent spectra consisted of the blue band (maximum at 456 nm) and the red band (650 nm) in the visible range. It was shown that increase in the absorption dose had an effect on the silica luminescence. It was found that the most significant changes in the spectrum occurred during the dose accumulation in the region of 550–700 nm. The shape of the spectrum of the luminescent radiation in this wavelength range was affected both by the oxygen deficient centres (blue band) and non-bridging oxygen hole centers (red band). Mathematical processing of the experimental spectra permitted to identify contributions to the luminescent radiation coming from both types of defects.

Mots clés

  • luminescent spectrum
  • absorption dose
  • ion implantation
  • silica
Accès libre

Study of tungsten surface interaction with plasma streams at DPF-1000U

Publié en ligne: 22 Jun 2015
Pages: 293 - 296

Résumé

Abstract

In this note experimental studies of tungsten (W) samples irradiated by intense plasma-ion streams are reported. Measurements were performed using the modified plasma focus device DPF-1000U equipped with an axial gas-puffing system. The main diagnostic tool was a Mechelle®900 optical spectrometer. The electron density of a freely propagating plasma stream (i.e., the plasma stream observed without any target inside the vacuum chamber) was estimated on the basis of the half-width of the Dβ spectral line, taking into account the linear Stark effect. For a freely propagating plasma stream the maximum electron density amounted to about 1.3 × 1017 cm−3 and was reached during the maximum plasma compression. The plasma electron density depends on the initial conditions of the experiments. It was thus important to determine first the plasma flow characteristics before attempting any target irradiation. These data were needed for comparison with plasma characteristics after an irradiation of the investigated target. In fact, spectroscopic measurements performed during interactions of plasma streams with the investigated W samples showed many WI and WII spectral lines. The surface erosion was determined from mass losses of the irradiated samples. Changes on the surfaces of the irradiated samples were also investigated with an optical microscope and some sputtering and melting zones were observed.

Mots clés

  • DPF-1000U
  • electron density
  • gas-puffing
  • plasma stream
  • tungsten
Accès libre

Recent ion measurements within the modified DPF-1000U facility

Publié en ligne: 22 Jun 2015
Pages: 297 - 302

Résumé

Abstract

In this note we describe measurements of ion beams emitted along the z-axis of the DPF-1000U facility operated at 23 kV, 334 kJ, and with the initial deuterium pressure of 1.6–2 hPa. The DPF-1000U device was recently renewed and equipped with a dynamic gas-puff valve placed inside the inner electrode. The investigated ions were recorded by means of ion pinhole cameras equipped with solid state nuclear track detectors of the PM-355® (PADC) type. The energy spectra of ions were determined using a Thomson spectrometer placed on the symmetry axis at a distance of 160 cm from the electrodes outlets. The ion images recorded during discharges performed under different experimental conditions show that the ion beams have a complex structure, usually in the form of a central bunch and an annular stream composed of many micro-beams. Energies of the registered deuterons have been in the range of 30–700 keV, while the fast protons (which originated from the hydrogen remnants) had energies in the range of 300–850 keV.

Mots clés

  • DPF-1000U facility
  • ion beams
  • ion energy spectra
  • ion pinhole images
Accès libre

Recent measurements of soft X-ray emission from the DPF-1000U facility

Publié en ligne: 22 Jun 2015
Pages: 303 - 308

Résumé

Abstract

Soft X-ray imaging is a very useful diagnostic technique in plasma-focus (PF) experiments. This paper reports results of four experimental sessions which were carried out at the DPF-1000U plasma-focus facility in 2013 and 2014. Over 200 discharges were performed at various experimental conditions. Measurements were taken using two X-ray pinhole cameras with a line of sight perpendicular to the z-axis, at different azimuthal angles (about 20° and 200°), and looking towards the centre of the PF-pinch column. They were equipped with diaphragms 1000 μm or 200–300 μm in diameter and coated with filters of 500 μm Al foil and 10 μm Be foil, respectively. Data on the neutron emission were collected with silver activation counters. For time-resolved measurements the use was made of four PIN diodes equipped with various filters and oriented towards the centre of the PF-column, in the direction perpendicular to the electrode axis. The recorded X-ray images revealed that when the additional gas-puff system is activated during the discharge, the stability of the discharge is improved. The data collected in these experiments confirmed the appearance of a filamentary fine structure in the PF discharges. In the past years the formation of such filaments was observed in many Z-pinch type experiments. Some of the recorded X-ray images have also revealed the appearance of the so-called hot-spots, i.e. small plasma regions of a very intense X-ray emission. Such a phenomenon was observed before in many PF experiments, e.g. in the MAJA-PF device, but it has not been investigated so far in a large facility such as the DPF-1000U. The time-resolved measurements provided the evidence of a time lapse between the X-ray emission from plasma regions located at different distance from the anode surface. The formation of distinct ‘hot-spots’ in different instants of the DPF-1000U discharge was also observed.

Mots clés

  • plasma focus
  • X-ray emission
  • X-ray images
  • gas-puffing
  • filaments
  • hot-spots
Accès libre

Comparison of optical spectra recorded during DPF-1000U plasma experiments with gas-puffing

Publié en ligne: 22 Jun 2015
Pages: 309 - 314

Résumé

Abstract

The results are presented of the optical spectra measurements for free plasma streams generated with the use of the modified DPF-1000U machine. This facility was recently equipped with a gas injection system (the so-called gas-puff) placed on the symmetry axis behind the central opening in the inner electrode. The DPF-1000U experimental chamber was filled up with pure deuterium at the initial pressure of 1.6 or 2.4 mbar. Additionally, when the use was made of the gas-puff system about 1 cm3 of pure deuterium was injected at the pressure of 2 bars. The gas injection was initiated 1.5 or 2 ms before the triggering of the main discharge. The investigated plasma discharges were powered from a condenser bank charged initially to 23 kV (corresponding to the energy of 352 kJ), and the maximum discharge current amounted to about 1.8 MA. In order to investigate properties of a dense plasma column formed during DPF-1000U discharges the use was made of the optical emission spectroscopy. The optical spectra were recorded along the line of sight perpendicular to the vacuum chamber, using a Mechelle®900 spectrometer. The recent analysis of all the recorded spectra made it possible to compare the temporal changes in the electron density of a freely propagating plasma stream for discharges without and with the gas-puffing. Using this data an appropriate mode of operation of the DPF-1000U facility could be determined.

Mots clés

  • electron density
  • gas-puff
  • optical spectrum
  • plasma focus
  • plasma stream
Accès libre

Temporal distribution of linear densities of the plasma column in a plasma focus discharge

Publié en ligne: 22 Jun 2015
Pages: 315 - 318

Résumé

Abstract

Experiments were carried out on the PF-1000 plasma focus device, with a deuterium filling and with deuterium puffing from a gas-puff nozzle placed on the axis of the anode face. The current was reaching 2 MA. 15 interferometric frames from one shot were recorded with a Nd:YLF laser and a Mach–Zehnder interferometer, with 10–20 ns delay between the frames. As a result, the temporal and spatial distribution of the linear densities and the radial and axial velocities of the moving of plasma in the dense plasma column could be estimated.

Mots clés

  • plasma focus (PF)
  • plasma pinch
  • plasma diagnostics
Accès libre

Determination of the emission rate for the 14 MeV neutron generator with the use of radio-yttrium

Publié en ligne: 22 Jun 2015
Pages: 319 - 322

Résumé

Abstract

The neutron emission rate is a crucial parameter for most of the radiation sources that emit neutrons. In the case of large fusion devices the determination of this parameter is necessary for a proper assessment of the power release and the prediction for the neutron budget. The 14 MeV neutron generator will be used for calibration of neutron diagnostics at JET and ITER facilities. The stability of the neutron generator working parameters like emission and angular homogeneity affects the accuracy of calibration other neutron diagnostics. The aim of our experiment was to confirm the usefulness of yttrium activation method for monitoring of the neutron generator SODERN Model: GENIE 16. The reaction rate induced by neutrons inside the yttrium sample was indirectly measured by activation of the yttrium sample, and then by means of the γ-spectrometry method. The pre-calibrated HPGe detector was used to determine the yttrium radioactivity. The emissivity of neutron generator calculated on the basis of the measured radioactivity was compared with the value resulting from its electrical settings, and both of these values were found to be consistent. This allowed for a positive verification of the reaction cross section that was used to determine the reaction rate (6.45 × 10−21 reactions per second) and the neutron emission rate (1.04 × 108 n·s−1). Our study confirms usefulness of the yttrium activation method for monitoring of the neutron generator.

Mots clés

  • 14 MeV neutron generator
  • activation method
  • yttrium activation
Accès libre

MCNP calculations of neutron emission anisotropy caused by the GIT-12 hardware

Publié en ligne: 22 Jun 2015
Pages: 323 - 326

Résumé

Abstract

The MCNP6 and MCNPX calculations for the GIT-12 device in Tomsk were performed to determine the influence of the gas-puff hardware on the neutron emission anisotropy and the neutron scattering rate. A monoenergetic 2.45 MeV neutron source and F1 and F6 tallies were declared in the simulation input. A comparison between MCNP results and the measured data was made. Differences between MCNPX and MCNP6 output data were investigated. In the experiment, two nTOF scintillation detectors with the Bicron BC-408 scintillator were used to measure the neutron waveform. Four bubble BD-PND detectors were used to estimate the amount of neutrons in different places around the neutron source.

Mots clés

  • Z-pinch
  • gas-puff
  • MCNP
Accès libre

Operation modes of the FALCON ion source as a part of the AMS cluster tool

Publié en ligne: 22 Jun 2015
Pages: 327 - 330

Résumé

Abstract

The paper investigates the options to increase the production yield of temperature compensated surface acoustic wave (SAW) devices with a defined range of operational frequencies. The paper focuses on the preparation of large wafers with SiO2 and AlN/Si3N4 depositions. Stability of the intermediate SiO2 layer is achieved by combining high power density UV radiation with annealing in high humidity environment. A uniform thickness of the capping AlN layer is achieved by local high-rate etching with a focused ion beam emitted by the FALCON ion source. Operation parameters and limitations of the etching process are discussed.

Mots clés

  • FALCON
  • ion sourcem
  • surface wave
  • cluster tool
Accès libre

Important problems of future thermonuclear reactors*

Publié en ligne: 22 Jun 2015
Pages: 331 - 338

Résumé

Abstract

This paper concerns important and difficult problems connected with a design and construction of thermonuclear reactors, which have to use nuclear fusion reactions of heavy isotopes of hydrogen, i.e., deuterium (D) and tritium (T). There are described conditions in which such reactions can occur, and different methods of a high-temperature plasma generation, i.e., high-current electrical discharges, intense microwave pulses, and injection of energetic neutral atoms (NBI). There are also presented experimental facilities which can contain hot plasma for an appropriate period, and particularly so-called tokamaks. The second part presents the technical problems which must be solved in order to build a thermonuclear reactor, that might be used for energetic purposes. There are considered problems connected with a choice of constructional materials for a vacuum chamber, its internal parts, external windings generating a magnetic field, and necessary shields. The next part considers the handling of radioactive tritium; the using of alpha particles (4He) for additional heating of plasma; recuperation of hydrogen isotopes absorbed in the tokamak internal parts, and a removal of a helium excess. There is presented a scheme of a future thermonuclear power plant and critical comments on a road map which should enable the construction of an industrial thermonuclear reactor (DEMO).

Mots clés

  • fusion reactions
  • plasma
  • tokamak
  • power plant
  • thermonuclear reactor
Accès libre

Evaluation of passive autocatalytic recombiners operation efficiency by means of the lumped parameter approach*

Publié en ligne: 22 Jun 2015
Pages: 339 - 345

Résumé

Abstract

The problem of hydrogen behavior in containment buildings of nuclear reactors belongs to thermal-hydraulic area. Taking into account the size of systems under consideration and, first of all, safety issues, such type of analyses cannot be done by means of full-scale experiments. Therefore, mathematical modeling and numerical simulations are widely used for these purposes. A lumped parameter approach based code HEPCAL has been elaborated in the Institute of Thermal Technology of the Silesian University of Technology for simulations of pressurized water reactor containment transient response. The VVER-440/213 and European pressurised water reactor (EPR) reactors containments are the subjects of analysis within the framework of this paper. Simulations have been realized for the loss-of-coolant accident scenarios with emergency core cooling system failure. These scenarios include core overheating and hydrogen generation. Passive autocatalytic recombiners installed for removal of hydrogen has been taken into account. The operational efficiency of the hydrogen removal system has been evaluated by comparing with an actual hydrogen concentration and flammability limit. This limit has been determined for the three-component mixture of air, steam and hydrogen. Some problems related to the lumped parameter approach application have been also identified.

Mots clés

  • hydrogen
  • lumped parameter modeling
  • nuclear reactor
  • passive autocatalytic recombiners
Accès libre

CFD modeling of passive autocatalytic recombiners*

Publié en ligne: 22 Jun 2015
Pages: 347 - 353

Résumé

Abstract

This study deals with numerical modeling of passive autocatalytic hydrogen recombiners (PARs). Such devices are installed within containments of many nuclear reactors in order to remove hydrogen and convert it to steam. The main purpose of this work is to develop a numerical model of passive autocatalytic recombiner (PAR) using the commercial computational fluid dynamics (CFD) software ANSYS-FLUENT and tuning the model using experimental results. The REKO 3 experiment was used for this purpose. Experiment was made in the Institute for Safety Research and Reactor Technology in Julich (Germany). It has been performed for different hydrogen concentrations, different flow rates, the presence of steam, and different initial temperatures of the inlet mixture. The model of this experimental recombiner was elaborated within the framework of this work. The influence of mesh, gas thermal conductivity coefficient, mass diffusivity coefficients, and turbulence model was investigated. The best results with a good agreement with REKO 3 data were received for k-ɛ model of turbulence, gas thermal conductivity dependent on the temperature and mass diffusivity coefficients taken from CHEMKIN program. The validated model of the PAR was next implemented into simple two-dimensional simulations of hydrogen behavior within a subcompartment of a containment building.

Mots clés

  • nuclear reactor
  • hydrogen
  • passive autocatalytic recombiners
  • CFD modeling
Accès libre

Enhanced resonant second harmonic generation in plasma based on density transition

Publié en ligne: 22 Jun 2015
Pages: 355 - 360

Résumé

Abstract

Resonant second harmonic generation of a relativistic self-focusing laser in plasma with density ramp profile has been investigated. A high intense Gaussian laser beam generates resonant second harmonic beam in plasma with density ramp profile. The second harmonic undergoes periodic focusing in the plasma channel created by the fundamental wave. The normalized second harmonic amplitude varies periodically with distance and attains maximum value in the focal region. Enhancement in the second harmonic amplitude on account of relativistic self-focusing of laser based on plasma density transition is seen. Plasma density ramp plays an important role to make self-focusing stronger which leads to enhance the second harmonic generation in plasma.

Mots clés

  • second harmonic generation
  • laser
  • plasma density ramp
  • self-focusing
Accès libre

Monte Carlo study of medium-energy electron penetration in aluminium and silver

Publié en ligne: 22 Jun 2015
Pages: 361 - 366

Résumé

Abstract

Monte Carlo simulations are very useful for many physical processes. The transport of particles was simulated by Monte Carlo calculating the basic parameters such as probabilities of transmitted–reflected and angular-energy distributions after interaction with matter. Monte Carlo simulations of electron scattering based on the single scattering model were presented in the medium-energy region for aluminium and silver matters. Two basic equations are required the elastic scattering cross section and the energy loss. The Rutherford equation for the different screening parameters is investigated. This scattering model is accurate in the energy range from a few keV up to about 0.50 MeV. The reliability of the simulation method is analysed by comparing experimental data from transmission measurements.

Mots clés

  • angular distribution
  • electron
  • energy spectra
  • penetration
  • transmission
Accès libre

Neutronic analysis for core conversion (HEU–LEU) of the low power research reactor using the MCNP4C code

Publié en ligne: 22 Jun 2015
Pages: 367 - 371

Résumé

Abstract

Comparative studies for conversion of the fuel from HEU to LEU in the miniature neutron source reactor (MNSR) have been performed using the MCNP4C code. The HEU fuel (UAl4-Al, 90% enriched with Al clad) and LEU (UO2 12.6% enriched with zircaloy-4 alloy clad) cores have been analyzed in this study. The existing HEU core of MNSR was analyzed to validate the neutronic model of reactor, while the LEU core was studied to prove the possibility of fuel conversion of the existing HEU core. The proposed LEU core contained the same number of fuel pins as the HEU core. All other structure materials and dimensions of HEU and LEU cores were the same except the increase in the radius of control rod material from 0.195 to 0.205 cm and keeping the outer diameter of the control rod unchanged in the LEU core. The effective multiplication factor (keff), excess reactivity (ρex), control rod worth (CRW), shutdown margin (SDM), safety reactivity factor (SRF), delayed neutron fraction (βeff) and the neutron fluxes in the irradiation tubes for the existing and the potential LEU fuel were investigated. The results showed that the safety parameters and the neutron fluxes in the irradiation tubes of the LEU fuels were in good agreements with the HEU results. Therefore, the LEU fuel was validated to be a suitable choice for fuel conversion of the MNSR in the future.

Mots clés

  • MNSR reactor
  • HEU fuel
  • LEU fuel
  • MCNP4C code
  • safety parameters
Accès libre

Erratum to “Subsurface structure and magnetic parameters of Fe–Mo–Cu–B metallic glass” [Nukleonika 2015;60(1):115-119]

Publié en ligne: 22 Jun 2015
Pages: 372 - 372

Résumé

31 Articles
Accès libre

Generation of shock waves in dense plasmas by high-intensity laser pulses

Publié en ligne: 22 Jun 2015
Pages: 193 - 198

Résumé

Abstract

When intense short-pulse laser beams (I > 1022 W/m2, τ < 20 ps) interact with high density plasmas, strong shock waves are launched. These shock waves may be generated by a range of processes, and the relative significance of the various mechanisms driving the formation of these shock waves is not well understood. It is challenging to obtain experimental data on shock waves near the focus of such intense laser–plasma interactions. The hydrodynamics of such interactions is, however, of great importance to fast ignition based inertial confinement fusion schemes as it places limits upon the time available for depositing energy in the compressed fuel, and thereby directly affects the laser requirements. In this manuscript we present the results of magnetohydrodynamic simulations showing the formation of shock waves under such conditions, driven by the j × B force and the thermal pressure gradient (where j is the current density and B the magnetic field strength). The time it takes for shock waves to form is evaluated over a wide range of material and current densities. It is shown that the formation of intense relativistic electron current driven shock waves and other related hydrodynamic phenomena may be expected over time scales of relevance to intense laser–plasma experiments and the fast ignition approach to inertial confinement fusion. A newly emerging technique for studying such interactions is also discussed. This approach is based upon Doppler spectroscopy and offers promise for investigating early time shock wave hydrodynamics launched by intense laser pulses.

Mots clés

  • shock waves
  • radiation hydrodynamics
  • laser–plasma interactions
  • fast ignition
  • inertial confinement fusion
  • Doppler spectroscopy
Accès libre

Selected methods of electron-and ion-diagnostics in tokamak scrape-off-layer

Publié en ligne: 22 Jun 2015
Pages: 199 - 206

Résumé

Abstract

This invited paper considers reasons why exact measurements of fast electron and ion losses in tokamaks, and particularly i n a scrape-off-layer and near a divertor region, are necessary in order to master nuclear fusion energy production. Attention is also paid to direct measurements of escaping fusion products from D-D and D-T reactions, and in particular of fast alphas which might be used for plasma heating. The second part describes the generation of so-called runaway and ripple-born electrons which might induce high energy losses and cause severe damages of internal walls in fusion facilities. Advantages and disadvantages of different diagnostic methods applied for studies of such fast electrons are discussed. Particular attention is paid to development of a direct measuring technique based on the Cherenkov effect which might be induced by fast electrons in appropriate radiators. There are presented various versions of Cherenkov-type probes which have been developed by the NCBJ team and applied in different tokamak experiments. The third part is devoted to direct measurements of fast ions (including those produced by the nuclear fusion reactions) which can escape from a high-temperature plasma region. Investigation of fast fusion-produced protons from tokamak discharges is reported. New ion probes, which were developed by the NCBJ team, are also presented. For the first time there is given a detailed description of an ion pinhole camera, which enables irradiation of several nuclear track detectors during a single tokamak discharge, and a miniature Thomson-type mass-spectrometer, which can be used for ion measurements at plasma borders.

Mots clés

  • diagnostics
  • electrons
  • ions
  • fusion products
  • probes
  • tokamak
Accès libre

Ion acceleration from intense laser-generated plasma: methods, diagnostics and possible applications

Publié en ligne: 22 Jun 2015
Pages: 207 - 212

Résumé

Abstract

Many parameters of non-equilibrium plasma generated by high intensity and fast lasers depend on the pulse intensity and the laser wavelength. In conditions favourable for the target normal sheath acceleration (TNSA) regime the ion acceleration from the rear side of the target can be enhanced by increasing the thin foil absorbance through the use of nanoparticles and nanostructures promoting the surface plasmon resonance effect. In conditions favourable for the backward plasma acceleration (BPA) regime, when thick targets are used, a special role is played by the laser focal position with respect to the target surface, a proper choice of which may result in induced self-focusing effects and non-linear acceleration enhancement. SiC detectors employed in the time-of-flight (TOF) configuration and a Thomson parabola spectrometer permit on-line diagnostics of the ion streams emitted at high kinetic energies. The target composition and geometry, apart from the laser parameters and to the irradiation conditions, allow further control of the plasma characteristics and can be varied by using advanced targets to reach the maximum ion acceleration. Measurements using advanced targets with enhanced the laser absorption effect in thin films are presented. Applications of accelerated ions in the field of ion source, hadrontherapy and nuclear physics are discussed.

Mots clés

  • ion acceleration in plasma
  • plasma diagnostics
  • TOF
  • target normal sheath acceleration (TNSA)
Accès libre

Shock dynamics induced by double-spot laser irradiation of layered targets

Publié en ligne: 22 Jun 2015
Pages: 213 - 219

Résumé

Abstract

We studied the interaction of a double-spot laser beam with targets using the Prague Asterix Laser System (PALS) iodine laser working at 0.44 μm wavelength and intensity of about 1015 W/cm2. Shock breakout signals were recorder using time-resolved self-emission from target rear side of irradiated targets. We compared the behavior of pure Al targets and of targets with a foam layer on the laser side. Results have been simulated using hydrodynamic numerical codes.

Mots clés

  • laser shock
  • high pressures
  • non-uniformity smoothing
Accès libre

The source of X-rays and high-charged ions based on moderate power vacuum discharge with laser triggering

Publié en ligne: 22 Jun 2015
Pages: 221 - 227

Résumé

Abstract

The source of X-ray radiation with the energy of quanta that may vary in the range hν = 1÷12 keV was developed for studies in X-ray interaction with matter and modification of solid surfaces. It was based on a vacuum spark discharge with the laser triggering. It was shown in our experiments that there is a possibility to adjust X-ray radiation spectrum by changing the configuration of the electrode system when the energy stored in the capacitor is varied within the range of 1÷17 J. A comprehensive study of X-ray imaging and quanta energy was carried out. These experiments were carried out for the case of both direct and reverse polarity of the voltage on the electrodes. Additionally, ion composition of plasma created in a laser-triggered vacuum discharge was analyzed. Highly charged ions Zn(+21), Cu(+20) and Fe(+18) were observed.

Mots clés

  • laser-triggered vacuum discharge
  • sources of X-rays
  • ion composition of plasma
Accès libre

Numerical simulations of generation of high-energy ion beams driven by a petawatt femtosecond laser

Publié en ligne: 22 Jun 2015
Pages: 229 - 232

Résumé

Abstract

This contribution presents results of a Particle-in-Cell simulation of ion beam acceleration via the interaction of a petawatt 25 fs laser pulse of high intensity (up to ~1021 W/cm2) with thin hydrocarbon (CH) and erbium hydride (ErH3) targets of equal areal mass density (of 0.6 g/m2). A special attention is paid to the effect that the laser pulse polarization and the material composition of the target have on the maximum ion energies and the number of high energy (>10 MeV) protons. It is shown that both the mean and the maximum ion energies are higher for the linear polarization than for the circular one. A comparison of the maximum proton energies and the total number of protons generated from the CH and ErH3 targets using a linearly polarized beam is presented. For the ErH3 targets the maximum proton energies are higher and they reach 50 MeV for the laser pulse intensity of 1021 W/cm2. The number of protons with energies higher than 10 MeV is an order of magnitude higher for the ErH3 targets than that for the CH targets.

Mots clés

  • laser acceleration
  • laser plasma
  • ions
  • particle-in-cell simulations
Accès libre

Hot electron refluxing in the short intense laser pulse interactions with solid targets and its influence on K-α radiation

Publié en ligne: 22 Jun 2015
Pages: 233 - 237

Résumé

Abstract

Fast electrons created as a result of the laser beam interaction with a solid target penetrate into the target material and initialize processes leading to the generation of the characteristic X-ray K-α radiation. Due to the strong electric field induced at the rear side of a thin target the transmitted electrons are redirected back into the target. These refluxing electrons increase the K-α radiation yield, as well as the duration of the X-ray pulse and the size of the radiation emitting area. A model describing the electron refluxing was verified via particle-in-cell simulations for non-relativistic electron energies. Using this model it was confirmed that the effect of the electron refluxing on the generated X-ray radiation depends on the target thickness and the target material. A considarable increase of the number of the emitted K-α photons is observed especially for thin targets made of low-Z materials, and for higher hot electron temperatures.

Mots clés

  • electron recirculation
  • electron refluxing
  • K-α radiation
  • laser–plasma interactions
  • particle-in-cell simulation
Accès libre

Electromagnetic pulses produced by expanding laser-produced Au plasma

Publié en ligne: 22 Jun 2015
Pages: 239 - 243

Résumé

Abstract

The interaction of an intense laser pulse with a solid target produces large number of fast free electrons. This emission gives rise to two distinct sources of the electromagnetic pulse (EMP): the pulsed return current through the holder of the target and the outflow of electrons into the vacuum. A relation between the characteristics of laser-produced plasma, the target return current and the EMP emission are presented in the case of a massive Au target irradiated with the intensity of up to 3 × 1016 W/cm2. The emission of the EMP was recorded using a 12 cm diameter Moebius loop antennas, and the target return current was measured using a new type of inductive target probe (T-probe). The simultaneous use of the inductive target probe and the Moebius loop antenna represents a new useful way of diagnosing the laser–matter interaction, which was employed to distinguish between laser-generated ion sources driven by low and high contrast laser pulses.

Mots clés

  • laser-produced plasma
  • electromagnetic pulse (EMP)
  • return target current
  • Moebius loop antenna
  • inductive target probe
Accès libre

High Power Laser Laboratory at the Institute of Plasma Physics and Laser Microfusion: equipment and preliminary research

Publié en ligne: 22 Jun 2015
Pages: 245 - 248

Résumé

Abstract

The purpose of this paper is to present the newly-opened High Power Laser Laboratory (HPLL) at the Institute of Plasma Physics and Laser Microfusion (IPPLM). This article describes the laser, the main laboratory accessories and the diagnostic instruments. We also present preliminary results of the first experiment on ion and X-ray generation from laser-produced plasma that has been already performed at the HPLL.

Mots clés

  • femtosecond pulses
  • high-power laser
  • inertial confinement fusion
  • laser plasma
Accès libre

First dedicated observations of runaway electrons in the COMPASS tokamak

Publié en ligne: 22 Jun 2015
Pages: 249 - 255

Résumé

Abstract

Runaway electrons present an important part of the present efforts in nuclear fusion research with respect to the potential damage of the in-vessel components. The COMPASS tokamak a suitable tool for the studies of runaway electrons, due to its relatively low vacuum safety constraints, high experimental flexibility and the possibility of reaching the H-mode D-shaped plasmas. In this work, results from the first experimental COMPASS campaign dedicated to runaway electrons are presented and discussed in preliminary way. In particular, the first observation of synchrotron radiation and rather interesting raw magnetic data are shown.

Mots clés

  • plasma diagnostics
  • runaway electrons
  • tokamak
Accès libre

Liquid micro pulsed plasma thruster

Publié en ligne: 22 Jun 2015
Pages: 257 - 261

Résumé

Abstract

A new type of pulsed plasma thruster (PPT) for small satellite propulsion is investigated, of which the most innovative aspect is the use of a non-volatile liquid propellant. The thruster is based on an open capillary design. The thruster achieved a thrust-to-power ratio above 45 μN/W, which constitutes a 5-fold improvement over the water-propelled pulsed plasma thruster, and which is also slightly above the performance of a similarly sized PPT with a solid propellant.

Mots clés

  • electric propulsion
  • pulsed plasma thruster
  • liquid propellant
Accès libre

Second order reflection from crystals used in soft X-ray spectroscopy

Publié en ligne: 22 Jun 2015
Pages: 263 - 265

Résumé

Abstract

In this note the ratio of the second to the first order reflection is determined for the KAP and PbSt crystals, for wavelengths corresponding to the Al K-line emission. The source of the radiation was a low-voltage stabilized X-ray tube. The X-rays were detected with a Bragg spectrometer equipped with a proportional counter detector. The signal measured by the proportional counter was subsequently pulse height analyzed.

Mots clés

  • soft X-ray
  • plasma spectroscopy
  • PbSt
  • KAP
Accès libre

Overview of processing technologies for tungsten-steel composites and FGMs for fusion applications

Publié en ligne: 22 Jun 2015
Pages: 267 - 273

Résumé

Abstract

Tungsten is a prime candidate material for the plasma-facing components in future fusion devices, e.g. ITER and DEMO. Because of the harsh and complex loading conditions and the differences in material properties, joining of the tungsten armor to the underlying construction and/or cooling parts is a complicated issue. To alleviate the thermal stresses at the joint, a sharp interface may be replaced by a gradual one with a smoothly varying composition. In this paper, several techniques for the formation of tungsten-steel composites and graded layers are reviewed. These include plasma spraying, laser cladding, hot pressing and spark plasma sintering. Structure, composition and selected thermal and mechanical properties of representative layers produced by each of these techniques are presented. A summary of advantages and disadvantages of the techniques and an assessment of their suitability for the production of plasma-facing components is provided.

Mots clés

  • plasma-facing components
  • functionally graded materials (FGMs)
  • tungsten
  • steel
  • plasma spraying
  • powder metallurgy
Accès libre

Heat load and deuterium plasma effects on SPS and WSP tungsten

Publié en ligne: 22 Jun 2015
Pages: 275 - 283

Résumé

Abstract

Tungsten is a prime choice for armor material in future nuclear fusion devices. For the realization of fusion, it is necessary to address issues related to the plasma–armor interactions. In this work, several types of tungsten material were studied, i.e. tungsten prepared by spark plasma sintering (SPS) and by water stabilized plasma spraying (WSP) technique. An intended surface porosity was created in the samples to model hydrogen/helium bubbles. The samples were subjected to a laser heat loading and a radiation loading of deuterium plasma to simulate edge plasma conditions of a nuclear fusion device (power density of 108 W/cm2 and 107 W/cm2, respectively, in the pulse intervals up to 200 ns). Thermally induced changes in the morphology and the damage to the studied surfaces are described. Possible consequences for the fusion device operation are pointed out.

Mots clés

  • tungsten
  • fusion
  • heat loading
  • irradiation
  • bubbles
  • surface damage
Accès libre

R&D on divertor plasma facing components at the Institute for Plasma Research

Publié en ligne: 22 Jun 2015
Pages: 285 - 288

Résumé

Abstract

This paper is focused on various aspects of the development and testing of water cooled divertor PFCs. Divertor PFCs are mainly designed to absorb the heat and particle fluxes outflowing from the core plasma of fusion devices like ITER. The Divertor and First Wall Technology Development Division at the Institute for Plasma Research (IPR), India, is extensively working on development and testing of divertor plasma facing components (PFCs). Tungsten and graphite macro-brush type test mock-ups were produced using vacuum brazing furnace technique and tungsten monoblock type of test mock-ups were obtained by hot radial pressing (HRP) technique. Heat transfer performance of the developed test mock-ups was tested using high heat flux tests with different heat load conditions as well as the surface temperature monitoring using transient infrared thermography technique. Recently we have established the High Heat Flux Test Facility (HHFTF) at IPR with an electron gun EH300V (M/s Von Ardenne Anlagentechnik GmbH, Germany) having maximum power 200 kW. Two tungsten monoblock type test mock-ups were probed using HHFTF. Both of the test mock-ups successfully sustained 316 thermal cycles during high heat flux (HHF) tests. The test mock-ups were non-destructively tested using infrared thermography before and after the HHF tests. In this note we describe the detailed procedure used for testing macro-brush and monoblock type test mock-ups using in-house transient infrared thermography set-up. An acceptance criteria limit was defined for small scale macro-brush type of mock-ups using DTrefmax value and the surface temperature measured during the HHF tests. It is concluded that the heat transfer behavior of a plasma facing component was checked by the HHF tests followed by transient IR thermography. The acceptance criteria DTrefmax limit for a graphite macro-brush mock-up was found to be ~3°C while for a tungsten macro-brush mock-up it was ~5°C.

Mots clés

  • divertor
  • plasma facing material
  • high heat flux test
  • transient IR thermography
Accès libre

Change of silica luminescence due to fast hydrogen ion bombardment

Publié en ligne: 22 Jun 2015
Pages: 289 - 292

Résumé

Abstract

This paper deals with the luminescence of silica (KV-type) induced by beam of hydrogen ions with the energy of 210 keV per nucleon. An average implantation dose of up to 3.5 × 1021 cm−3 (5 × 1010 Gy) was accumulated during irradiation over an extended period. The luminescent spectra consisted of the blue band (maximum at 456 nm) and the red band (650 nm) in the visible range. It was shown that increase in the absorption dose had an effect on the silica luminescence. It was found that the most significant changes in the spectrum occurred during the dose accumulation in the region of 550–700 nm. The shape of the spectrum of the luminescent radiation in this wavelength range was affected both by the oxygen deficient centres (blue band) and non-bridging oxygen hole centers (red band). Mathematical processing of the experimental spectra permitted to identify contributions to the luminescent radiation coming from both types of defects.

Mots clés

  • luminescent spectrum
  • absorption dose
  • ion implantation
  • silica
Accès libre

Study of tungsten surface interaction with plasma streams at DPF-1000U

Publié en ligne: 22 Jun 2015
Pages: 293 - 296

Résumé

Abstract

In this note experimental studies of tungsten (W) samples irradiated by intense plasma-ion streams are reported. Measurements were performed using the modified plasma focus device DPF-1000U equipped with an axial gas-puffing system. The main diagnostic tool was a Mechelle®900 optical spectrometer. The electron density of a freely propagating plasma stream (i.e., the plasma stream observed without any target inside the vacuum chamber) was estimated on the basis of the half-width of the Dβ spectral line, taking into account the linear Stark effect. For a freely propagating plasma stream the maximum electron density amounted to about 1.3 × 1017 cm−3 and was reached during the maximum plasma compression. The plasma electron density depends on the initial conditions of the experiments. It was thus important to determine first the plasma flow characteristics before attempting any target irradiation. These data were needed for comparison with plasma characteristics after an irradiation of the investigated target. In fact, spectroscopic measurements performed during interactions of plasma streams with the investigated W samples showed many WI and WII spectral lines. The surface erosion was determined from mass losses of the irradiated samples. Changes on the surfaces of the irradiated samples were also investigated with an optical microscope and some sputtering and melting zones were observed.

Mots clés

  • DPF-1000U
  • electron density
  • gas-puffing
  • plasma stream
  • tungsten
Accès libre

Recent ion measurements within the modified DPF-1000U facility

Publié en ligne: 22 Jun 2015
Pages: 297 - 302

Résumé

Abstract

In this note we describe measurements of ion beams emitted along the z-axis of the DPF-1000U facility operated at 23 kV, 334 kJ, and with the initial deuterium pressure of 1.6–2 hPa. The DPF-1000U device was recently renewed and equipped with a dynamic gas-puff valve placed inside the inner electrode. The investigated ions were recorded by means of ion pinhole cameras equipped with solid state nuclear track detectors of the PM-355® (PADC) type. The energy spectra of ions were determined using a Thomson spectrometer placed on the symmetry axis at a distance of 160 cm from the electrodes outlets. The ion images recorded during discharges performed under different experimental conditions show that the ion beams have a complex structure, usually in the form of a central bunch and an annular stream composed of many micro-beams. Energies of the registered deuterons have been in the range of 30–700 keV, while the fast protons (which originated from the hydrogen remnants) had energies in the range of 300–850 keV.

Mots clés

  • DPF-1000U facility
  • ion beams
  • ion energy spectra
  • ion pinhole images
Accès libre

Recent measurements of soft X-ray emission from the DPF-1000U facility

Publié en ligne: 22 Jun 2015
Pages: 303 - 308

Résumé

Abstract

Soft X-ray imaging is a very useful diagnostic technique in plasma-focus (PF) experiments. This paper reports results of four experimental sessions which were carried out at the DPF-1000U plasma-focus facility in 2013 and 2014. Over 200 discharges were performed at various experimental conditions. Measurements were taken using two X-ray pinhole cameras with a line of sight perpendicular to the z-axis, at different azimuthal angles (about 20° and 200°), and looking towards the centre of the PF-pinch column. They were equipped with diaphragms 1000 μm or 200–300 μm in diameter and coated with filters of 500 μm Al foil and 10 μm Be foil, respectively. Data on the neutron emission were collected with silver activation counters. For time-resolved measurements the use was made of four PIN diodes equipped with various filters and oriented towards the centre of the PF-column, in the direction perpendicular to the electrode axis. The recorded X-ray images revealed that when the additional gas-puff system is activated during the discharge, the stability of the discharge is improved. The data collected in these experiments confirmed the appearance of a filamentary fine structure in the PF discharges. In the past years the formation of such filaments was observed in many Z-pinch type experiments. Some of the recorded X-ray images have also revealed the appearance of the so-called hot-spots, i.e. small plasma regions of a very intense X-ray emission. Such a phenomenon was observed before in many PF experiments, e.g. in the MAJA-PF device, but it has not been investigated so far in a large facility such as the DPF-1000U. The time-resolved measurements provided the evidence of a time lapse between the X-ray emission from plasma regions located at different distance from the anode surface. The formation of distinct ‘hot-spots’ in different instants of the DPF-1000U discharge was also observed.

Mots clés

  • plasma focus
  • X-ray emission
  • X-ray images
  • gas-puffing
  • filaments
  • hot-spots
Accès libre

Comparison of optical spectra recorded during DPF-1000U plasma experiments with gas-puffing

Publié en ligne: 22 Jun 2015
Pages: 309 - 314

Résumé

Abstract

The results are presented of the optical spectra measurements for free plasma streams generated with the use of the modified DPF-1000U machine. This facility was recently equipped with a gas injection system (the so-called gas-puff) placed on the symmetry axis behind the central opening in the inner electrode. The DPF-1000U experimental chamber was filled up with pure deuterium at the initial pressure of 1.6 or 2.4 mbar. Additionally, when the use was made of the gas-puff system about 1 cm3 of pure deuterium was injected at the pressure of 2 bars. The gas injection was initiated 1.5 or 2 ms before the triggering of the main discharge. The investigated plasma discharges were powered from a condenser bank charged initially to 23 kV (corresponding to the energy of 352 kJ), and the maximum discharge current amounted to about 1.8 MA. In order to investigate properties of a dense plasma column formed during DPF-1000U discharges the use was made of the optical emission spectroscopy. The optical spectra were recorded along the line of sight perpendicular to the vacuum chamber, using a Mechelle®900 spectrometer. The recent analysis of all the recorded spectra made it possible to compare the temporal changes in the electron density of a freely propagating plasma stream for discharges without and with the gas-puffing. Using this data an appropriate mode of operation of the DPF-1000U facility could be determined.

Mots clés

  • electron density
  • gas-puff
  • optical spectrum
  • plasma focus
  • plasma stream
Accès libre

Temporal distribution of linear densities of the plasma column in a plasma focus discharge

Publié en ligne: 22 Jun 2015
Pages: 315 - 318

Résumé

Abstract

Experiments were carried out on the PF-1000 plasma focus device, with a deuterium filling and with deuterium puffing from a gas-puff nozzle placed on the axis of the anode face. The current was reaching 2 MA. 15 interferometric frames from one shot were recorded with a Nd:YLF laser and a Mach–Zehnder interferometer, with 10–20 ns delay between the frames. As a result, the temporal and spatial distribution of the linear densities and the radial and axial velocities of the moving of plasma in the dense plasma column could be estimated.

Mots clés

  • plasma focus (PF)
  • plasma pinch
  • plasma diagnostics
Accès libre

Determination of the emission rate for the 14 MeV neutron generator with the use of radio-yttrium

Publié en ligne: 22 Jun 2015
Pages: 319 - 322

Résumé

Abstract

The neutron emission rate is a crucial parameter for most of the radiation sources that emit neutrons. In the case of large fusion devices the determination of this parameter is necessary for a proper assessment of the power release and the prediction for the neutron budget. The 14 MeV neutron generator will be used for calibration of neutron diagnostics at JET and ITER facilities. The stability of the neutron generator working parameters like emission and angular homogeneity affects the accuracy of calibration other neutron diagnostics. The aim of our experiment was to confirm the usefulness of yttrium activation method for monitoring of the neutron generator SODERN Model: GENIE 16. The reaction rate induced by neutrons inside the yttrium sample was indirectly measured by activation of the yttrium sample, and then by means of the γ-spectrometry method. The pre-calibrated HPGe detector was used to determine the yttrium radioactivity. The emissivity of neutron generator calculated on the basis of the measured radioactivity was compared with the value resulting from its electrical settings, and both of these values were found to be consistent. This allowed for a positive verification of the reaction cross section that was used to determine the reaction rate (6.45 × 10−21 reactions per second) and the neutron emission rate (1.04 × 108 n·s−1). Our study confirms usefulness of the yttrium activation method for monitoring of the neutron generator.

Mots clés

  • 14 MeV neutron generator
  • activation method
  • yttrium activation
Accès libre

MCNP calculations of neutron emission anisotropy caused by the GIT-12 hardware

Publié en ligne: 22 Jun 2015
Pages: 323 - 326

Résumé

Abstract

The MCNP6 and MCNPX calculations for the GIT-12 device in Tomsk were performed to determine the influence of the gas-puff hardware on the neutron emission anisotropy and the neutron scattering rate. A monoenergetic 2.45 MeV neutron source and F1 and F6 tallies were declared in the simulation input. A comparison between MCNP results and the measured data was made. Differences between MCNPX and MCNP6 output data were investigated. In the experiment, two nTOF scintillation detectors with the Bicron BC-408 scintillator were used to measure the neutron waveform. Four bubble BD-PND detectors were used to estimate the amount of neutrons in different places around the neutron source.

Mots clés

  • Z-pinch
  • gas-puff
  • MCNP
Accès libre

Operation modes of the FALCON ion source as a part of the AMS cluster tool

Publié en ligne: 22 Jun 2015
Pages: 327 - 330

Résumé

Abstract

The paper investigates the options to increase the production yield of temperature compensated surface acoustic wave (SAW) devices with a defined range of operational frequencies. The paper focuses on the preparation of large wafers with SiO2 and AlN/Si3N4 depositions. Stability of the intermediate SiO2 layer is achieved by combining high power density UV radiation with annealing in high humidity environment. A uniform thickness of the capping AlN layer is achieved by local high-rate etching with a focused ion beam emitted by the FALCON ion source. Operation parameters and limitations of the etching process are discussed.

Mots clés

  • FALCON
  • ion sourcem
  • surface wave
  • cluster tool
Accès libre

Important problems of future thermonuclear reactors*

Publié en ligne: 22 Jun 2015
Pages: 331 - 338

Résumé

Abstract

This paper concerns important and difficult problems connected with a design and construction of thermonuclear reactors, which have to use nuclear fusion reactions of heavy isotopes of hydrogen, i.e., deuterium (D) and tritium (T). There are described conditions in which such reactions can occur, and different methods of a high-temperature plasma generation, i.e., high-current electrical discharges, intense microwave pulses, and injection of energetic neutral atoms (NBI). There are also presented experimental facilities which can contain hot plasma for an appropriate period, and particularly so-called tokamaks. The second part presents the technical problems which must be solved in order to build a thermonuclear reactor, that might be used for energetic purposes. There are considered problems connected with a choice of constructional materials for a vacuum chamber, its internal parts, external windings generating a magnetic field, and necessary shields. The next part considers the handling of radioactive tritium; the using of alpha particles (4He) for additional heating of plasma; recuperation of hydrogen isotopes absorbed in the tokamak internal parts, and a removal of a helium excess. There is presented a scheme of a future thermonuclear power plant and critical comments on a road map which should enable the construction of an industrial thermonuclear reactor (DEMO).

Mots clés

  • fusion reactions
  • plasma
  • tokamak
  • power plant
  • thermonuclear reactor
Accès libre

Evaluation of passive autocatalytic recombiners operation efficiency by means of the lumped parameter approach*

Publié en ligne: 22 Jun 2015
Pages: 339 - 345

Résumé

Abstract

The problem of hydrogen behavior in containment buildings of nuclear reactors belongs to thermal-hydraulic area. Taking into account the size of systems under consideration and, first of all, safety issues, such type of analyses cannot be done by means of full-scale experiments. Therefore, mathematical modeling and numerical simulations are widely used for these purposes. A lumped parameter approach based code HEPCAL has been elaborated in the Institute of Thermal Technology of the Silesian University of Technology for simulations of pressurized water reactor containment transient response. The VVER-440/213 and European pressurised water reactor (EPR) reactors containments are the subjects of analysis within the framework of this paper. Simulations have been realized for the loss-of-coolant accident scenarios with emergency core cooling system failure. These scenarios include core overheating and hydrogen generation. Passive autocatalytic recombiners installed for removal of hydrogen has been taken into account. The operational efficiency of the hydrogen removal system has been evaluated by comparing with an actual hydrogen concentration and flammability limit. This limit has been determined for the three-component mixture of air, steam and hydrogen. Some problems related to the lumped parameter approach application have been also identified.

Mots clés

  • hydrogen
  • lumped parameter modeling
  • nuclear reactor
  • passive autocatalytic recombiners
Accès libre

CFD modeling of passive autocatalytic recombiners*

Publié en ligne: 22 Jun 2015
Pages: 347 - 353

Résumé

Abstract

This study deals with numerical modeling of passive autocatalytic hydrogen recombiners (PARs). Such devices are installed within containments of many nuclear reactors in order to remove hydrogen and convert it to steam. The main purpose of this work is to develop a numerical model of passive autocatalytic recombiner (PAR) using the commercial computational fluid dynamics (CFD) software ANSYS-FLUENT and tuning the model using experimental results. The REKO 3 experiment was used for this purpose. Experiment was made in the Institute for Safety Research and Reactor Technology in Julich (Germany). It has been performed for different hydrogen concentrations, different flow rates, the presence of steam, and different initial temperatures of the inlet mixture. The model of this experimental recombiner was elaborated within the framework of this work. The influence of mesh, gas thermal conductivity coefficient, mass diffusivity coefficients, and turbulence model was investigated. The best results with a good agreement with REKO 3 data were received for k-ɛ model of turbulence, gas thermal conductivity dependent on the temperature and mass diffusivity coefficients taken from CHEMKIN program. The validated model of the PAR was next implemented into simple two-dimensional simulations of hydrogen behavior within a subcompartment of a containment building.

Mots clés

  • nuclear reactor
  • hydrogen
  • passive autocatalytic recombiners
  • CFD modeling
Accès libre

Enhanced resonant second harmonic generation in plasma based on density transition

Publié en ligne: 22 Jun 2015
Pages: 355 - 360

Résumé

Abstract

Resonant second harmonic generation of a relativistic self-focusing laser in plasma with density ramp profile has been investigated. A high intense Gaussian laser beam generates resonant second harmonic beam in plasma with density ramp profile. The second harmonic undergoes periodic focusing in the plasma channel created by the fundamental wave. The normalized second harmonic amplitude varies periodically with distance and attains maximum value in the focal region. Enhancement in the second harmonic amplitude on account of relativistic self-focusing of laser based on plasma density transition is seen. Plasma density ramp plays an important role to make self-focusing stronger which leads to enhance the second harmonic generation in plasma.

Mots clés

  • second harmonic generation
  • laser
  • plasma density ramp
  • self-focusing
Accès libre

Monte Carlo study of medium-energy electron penetration in aluminium and silver

Publié en ligne: 22 Jun 2015
Pages: 361 - 366

Résumé

Abstract

Monte Carlo simulations are very useful for many physical processes. The transport of particles was simulated by Monte Carlo calculating the basic parameters such as probabilities of transmitted–reflected and angular-energy distributions after interaction with matter. Monte Carlo simulations of electron scattering based on the single scattering model were presented in the medium-energy region for aluminium and silver matters. Two basic equations are required the elastic scattering cross section and the energy loss. The Rutherford equation for the different screening parameters is investigated. This scattering model is accurate in the energy range from a few keV up to about 0.50 MeV. The reliability of the simulation method is analysed by comparing experimental data from transmission measurements.

Mots clés

  • angular distribution
  • electron
  • energy spectra
  • penetration
  • transmission
Accès libre

Neutronic analysis for core conversion (HEU–LEU) of the low power research reactor using the MCNP4C code

Publié en ligne: 22 Jun 2015
Pages: 367 - 371

Résumé

Abstract

Comparative studies for conversion of the fuel from HEU to LEU in the miniature neutron source reactor (MNSR) have been performed using the MCNP4C code. The HEU fuel (UAl4-Al, 90% enriched with Al clad) and LEU (UO2 12.6% enriched with zircaloy-4 alloy clad) cores have been analyzed in this study. The existing HEU core of MNSR was analyzed to validate the neutronic model of reactor, while the LEU core was studied to prove the possibility of fuel conversion of the existing HEU core. The proposed LEU core contained the same number of fuel pins as the HEU core. All other structure materials and dimensions of HEU and LEU cores were the same except the increase in the radius of control rod material from 0.195 to 0.205 cm and keeping the outer diameter of the control rod unchanged in the LEU core. The effective multiplication factor (keff), excess reactivity (ρex), control rod worth (CRW), shutdown margin (SDM), safety reactivity factor (SRF), delayed neutron fraction (βeff) and the neutron fluxes in the irradiation tubes for the existing and the potential LEU fuel were investigated. The results showed that the safety parameters and the neutron fluxes in the irradiation tubes of the LEU fuels were in good agreements with the HEU results. Therefore, the LEU fuel was validated to be a suitable choice for fuel conversion of the MNSR in the future.

Mots clés

  • MNSR reactor
  • HEU fuel
  • LEU fuel
  • MCNP4C code
  • safety parameters
Accès libre

Erratum to “Subsurface structure and magnetic parameters of Fe–Mo–Cu–B metallic glass” [Nukleonika 2015;60(1):115-119]

Publié en ligne: 22 Jun 2015
Pages: 372 - 372

Résumé

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