Menu
EN

Vyhledávání

Lidé

Ing. Karel Řezáč, Ph.D.

Všechny publikace

Hot electron emission characteristics from thin metal foil targets irradiated by terawatt laser

  • DOI: 10.1017/lpb.2023.2
  • Odkaz: https://doi.org/10.1017/lpb.2023.2
  • Pracoviště: Katedra fyziky
  • Anotace:
    The interaction of focused high power laser beam with solid targets leads to acceleration of charged particles among other by non-linear effects in the plasma. In this experiment, the hot electrons are characterized from the interaction of sub-nanosecond and kilo-joule class laser pulse with thin metal foil targets (Cu, Ta, Ti, Sn, Pb). The energy distribution functions of electrons were measured by angularly resolved multichannel electron spectrometer. The hot electron temperatures were observed in range from 30 to 80 keV for laser intensities between 10^15 and 3x10^16 Wcm^-2. The measured energy distribution and electron temperature were compared with published results and known scaling laws at higher laser intensities. For foil targets of different materials, the temperature and flux of hot electrons were scaled with target thickness in the range of 1-100 um from low Z to high Z materials where Z is the atomic number. The profile of conversion efficiency from laser energy to hot electrons is discussed in the energy range from 100 to 600 J. For the given laser and target parameters, the nonlinear behaviour of conversion efficiency and relevant physics are also described in detail.

Dynamics of implosion phase of modified plasma focus studied via laser interferometry and electrical measurements

  • DOI: 10.1063/5.0098124
  • Odkaz: https://doi.org/10.1063/5.0098124
  • Pracoviště: Katedra fyziky
  • Anotace:
    Dynamics of the implosion of the dense plasma focus play an essential role in converting electrical energy into the kinetic energy of the current sheath and subsequent production of accelerated electrons, ions, hard X-ray, and neutron emission. This paper presents the analysis of the implosion parameters, such as the implosion velocity and imploding mass, coupled with electrical parameters observed on the PF-1000 facility with a modified electrode system. The first two parameters are based on the 16-frame Mach–Zehnder interferometer, which provides the spatial distribution of electron density in a time sequence. Measurement of the total current, current derivative, and voltage enables us to evaluate the total inductance and kinetic energy driven by the capacitor bank. Then comparing the inductances and kinetic energies evaluated from the interferograms and electrical waveforms can provide more precise information on the current flowing in the imploding sheath. We present a possible way to deal with the fact that only part of the total current flows through the imploding layer. With the supposition that the rest of the current flows close to the insulator, we conclude that roughly 70% of the total current flows through the pinch, which is in good agreement with an input parameter of the Lee model, for example.

Temporal behavior of hard x-ray and neutron production in plasma focus discharges

  • DOI: 10.1063/5.0085351
  • Odkaz: https://doi.org/10.1063/5.0085351
  • Pracoviště: Katedra fyziky
  • Anotace:
    This paper concerns the correlation of hard x-ray and neutron signals, which were recorded with scintillation detectors oriented in the axial and radial directions, in a comparison with interferometric and extreme-ultraviolet radiation frames, as recorded within the plasma focus (PF)-1000 facility operated with a deuterium filling. The considered signals showed two different phases. In the initial phase, the fusion neutrons are mainly produced by deuterons moving dominantly downstream during the disruption of a pinch constriction (lasting tens nanoseconds). In the later phase (usually after about 100 ns), the fusion neutron emission reaches its maximum in the radial directions. This emission (lasting 100–200 ns) is caused by the fast deuterons moving in both the downstream and radial directions. It correlates usually with a decay of dense plasma structures in remnants of the expanding pinch column. This can be explained by a decay of internal magnetic fields. The neutron signal is usually composed of several sub-pulses of different energies. It was deduced that the primary deuterons producing the observed fusion neutrons undergo a regular and repeated temporal, directional, and energy evolution.

Ablation instability experimentally observed on the thin foil metal target surface during its irradiation by terawatt laser

  • Pracoviště: Katedra fyziky
  • Anotace:
    Time evolution of plasma density modulations in case of thin foil metal targets was observed during the irradiation with focused terawatt iodine PALS laser beam. These modulations were simultaneously recorded using femtosecond interferometry in three time frames and x-ray streak camera allowing to determine growth and decay rates of hydrodynamic instabilities. These modulations were observed during the laser-plasma interaction, in particular several hundred picoseconds before its maximum intensity. Hot electron emission characteristics were measured and analyzed using an angular array of electron spectrometers. Weaker emission of hot electrons from the lead plasma was observed in comparison to lower Z materials.

Characteristics of fast deuteron sources generated in a dense plasma focus

  • DOI: 10.1140/epjp/s13360-021-01799-w
  • Odkaz: https://doi.org/10.1140/epjp/s13360-021-01799-w
  • Pracoviště: Katedra fyziky
  • Anotace:
    The paper characterizes sources of the fast deuterons which can produce the D–D fusion neutrons. Two pinhole cameras, the axial one and the slant one (oriented at 0° and 60° in relation to the z-axis), were equipped with solid-state nuclear track detectors and applied to investigate the fast deuterons of energies about 100 keV, which produce small quasi-circular track spots of diameters ranging (1–3) mm. They are often observed in plasma-focus shots with higher neutron yields, when they constitute a part of the recorded ion images in a form of azimuthal arcs and/or radial strips. An analysis of an influence of the global magnetic field, which acts along the fast deuteron trajectories, made it possible to determinate the deuteron sources localization, also outside the dense plasma column. The recorded spatial distribution of the fast deuterons, their temporal correlation with disruptions of the ordered plasma structures inside and outside the pinch column, and a regular evolution of the energy of fast deuterons—indicate their strong interconnection and the link with filamentary structure of the current flow.

K-shell radiation and neutron emission from z-pinch plasmas generated by hybrid gas-puff implosions onto on-axis wires

  • DOI: 10.1063/5.0054683
  • Odkaz: https://doi.org/10.1063/5.0054683
  • Pracoviště: Katedra fyziky
  • Anotace:
    Z-pinches have been explored as efficient soft x-ray sources for many years. To optimize x-ray emission, various z-pinch configurations were tested. This paper presents data obtained with a hybrid gas-puff z-pinch imploding onto on-axis wires on a microsecond, multi-megaampere GIT-12 generator. In our previous experiments, the hybrid gas puff, i.e., an inner deuterium gas puff surrounded by an outer hollow cylindrical plasma shell, was used to produce energetic protons, deuterons, and neutrons up to 60MeV [Klir et al., New J. Phys. 22, 103036 (2020)]. The behavior of the hybrid gas-puff z-pinch on GIT-12 was interpreted as a high-density plasma opening switch with a microsecond conduction time, 3 MA conduction current, nanosecond opening, and up to 60MV stand-off voltage. These properties can be employed to transfer the current into an on-axis load with a high rise rate. In the recent experiments on GIT-12, we therefore placed single or multiple aluminum wires on the axis of the hybrid gas-puff z-pinch. Before a current sheath arrived at the axis, a coronal plasma was seen around the wire. A rapid increase in x-ray radiation was observed when the coronal plasma imploded onto the axis. The coronal plasma implosion resulted in a long (2cm), narrow (similar to mm) column radiating in the Al K-shell lines. With the single Al wire of 80 mu m diameter, the K-shell x-ray output reached 5.5 +/- 0.8kJ in a 0.6 +/- 0.1 TW peak power and 7 +/- 1ns pulse. The higher K-shell yield of 12 +/- 2kJ and peak K-shell power of 0.7 +/- 0.1 TW were achieved with four 38 mu m diameter Al wires. (Their cross section formed the corners of a square with 1mm side.) The presence of the wires on the axis significantly suppressed ion acceleration and neutron production. Deuterium-deuterium (DD) neutron yields of about 1.2x10(11) were 20 times smaller than the yields produced in shots without any wire. The DD neutron yield was increased up to 4.5x10(11) when the Al wire was replaced by a fiber fr

Mapping of azimuthal B-fields in Z-pinch plasmas using Z-pinch-driven ion deflectometry

  • DOI: 10.1063/5.0040515
  • Odkaz: https://doi.org/10.1063/5.0040515
  • Pracoviště: Katedra fyziky
  • Anotace:
    B-field measurements are crucial for the study of high-temperature and high-energy-density plasmas. A successful diagnostic method, ion deflectometry (radiography), is commonly employed to measure MGauss magnetic fields in laser-produced plasmas. It is based on the detection of multi-MeV ions, which are deflected in B-fields and measure their path integral. Until now, protons accelerated via laser–target interactions from a point-like source have been utilized for the study of Z-pinch plasmas. In this paper, we present the results of the first Z-pinch-driven ion deflectometry experiments using MeV deuterium beams accelerated within a hybrid gas-puff Z-pinch plasma on the GIT-12 pulse power generator. In our experimental setup, an inserted fiducial deflectometry grid (D-grid) separates the imploding plasma into two regions of the deuteron source and the studied azimuthal B-fields. The D-grid is backlighted by accelerated ions, and its shadow imprinted into the deuteron beams demonstrates ion deflections. In contrast to the employment of the conventional point-like ion source, in our configuration, the ions are emitted from the extensive and divergent source inside the Z-pinch. Instead of having the point ion source, deflected ions are selected via a point projection by a pinhole camera before their detection. Radial distribution of path-integrated B-fields near the axis (within a 15 mm radius) is obtained by analysis of experimental images (deflectograms). Moreover, we present a 2D topological map of local azimuthal B-fields B(r,z) via numerical retrieval of the experimental deflectogram.

Optimizing of Experimental Load of PFZ-200 Plasma Focus

  • DOI: 10.1109/TPS.2020.3041329
  • Odkaz: https://doi.org/10.1109/TPS.2020.3041329
  • Pracoviště: Katedra fyziky
  • Anotace:
    This article presents a study of neutron emission on the PFZ-200 plasma focus at the Department of physics on FEE CTU in Prague, Czech Republic. In order to achieve the highest and most stable neutron yields, the deuterium working gas pressure and the anode shape were systematically varied. We observed the plasma time to the pinch and the discharge current by the Rogowski coil and neutron emission by the silver activation detector and scintillation time-of-flight detectors. The imploded plasma was visualized using a fast X-ray pinhole camera with a gated microchannel plate detector. The experiment presents the z-pinch discharges with the current maximum above 200 kA and the average neutron yields of 3×10^8 neutrons/shot. Measured pinch times were in the range from 1.65 to 1.85 μs . The hollow round anode configuration performed the most stable neutron yields with a deviation under 20%.

Characteristics of closed currents and magnetic fields outside the dense pinch column in a plasma focus discharge

  • DOI: 10.1063/5.0010249
  • Odkaz: https://doi.org/10.1063/5.0010249
  • Pracoviště: Katedra fyziky
  • Anotace:
    This paper describes the structure of a higher extreme ultraviolet (XUV) emission and plasma density region which surrounds a pinched dense-plasma column. It is interpreted as a toroidal-like plasma formation, which is flowing by a closed current with poloidal and toroidal components upon its surface. This current produces a local magnetic field, which separates the external discharge current from the surface of the dense pinch column. We estimated the values of closed currents as well as magnetic- and plasma-pressures in this column and its surrounding on the basis of the measured distribution of interferometric fringes and intense XUV emission, recorded during the pinch stagnation phase. The considered layer forms the region in which the magnetic energy can be conserved, and during its decay, the acceleration of fast deuterons can take place.

Effect of expanding plasma on propagation of electromagnetic pulses by laser-plasma interaction

  • DOI: 10.1088/1361-6587/ab5c4e
  • Odkaz: https://doi.org/10.1088/1361-6587/ab5c4e
  • Pracoviště: Katedra fyziky
  • Anotace:
    Experiments were performed using the Prague Asterix Laser System to study the effect of expanding plasma on electromagnetic pulse propagation (EMP) in the interaction chamber in an intensity regime of 10(16)Wcm(-2). Similar to the interaction that occurs between radio waves and the ionosphere, the expansion of laser-produced plasma causes the vacuum chamber to be gradually filled with inhomogeneous plasma that interacts with the emitted EMP. Combining the space-time analysis of a plasma density inside the interaction chamber and the fast Fourier transform filtering of antenna signals, we have resolved the influence of the expanding plasma on space-time characteristics of EMP.

Ion acceleration and neutron production in hybrid gas-puff z-pinches on the GIT-12 and HAWK generators

  • DOI: 10.1063/1.5132845
  • Odkaz: https://doi.org/10.1063/1.5132845
  • Pracoviště: Katedra fyziky
  • Anotace:
    Z- pinch experiments with a hybrid configuration of a deuterium gas puff have been carried out on the HAWK (NRL, Washington, DC) and GIT-12 (IHCE, Tomsk) pulsed power generators at 0.7 MA and 3 MA currents, respectively. On GIT-12, neutron yields reached an average value of 2 X 10(12) neutrons, and deuterons were accelerated up to an energy of 30 MeV. This was 50 times the ion energy provided by the generator driving voltage of 0.6 MV and the highest energy observed in z-pinches and dense plasma foci. To confirm these unique results independently on another device, we performed several experimental campaigns on the HAWK generator. Comparison of the experiments on GIT-12 and HAWK helped us to understand which parameters are essential for optimized neutron production. Since the HAWK generator is of a similar pulsed power architecture as GIT-12, the experiments on GIT-12 and HAWK are important for the study of how charged-particle acceleration scales with the current. (C) 2020 Author(s).

Ion bursts and multi-electron population in expanding laser-produced plasma

  • DOI: 10.1088/1748-0221/15/05/C05046
  • Odkaz: https://doi.org/10.1088/1748-0221/15/05/C05046
  • Pracoviště: Katedra fyziky
  • Anotace:
    We present an experimental study of emission of relativistic electrons, fast ions and DD-fusion neutrons produced by interaction of sub-nanosecond laser radiation with solid targets performed at the PALS facility. Measurements of electron density close to the target surface using the femtosecond interferometry, energy distribution functions of hot electrons far from the target, and time-of-flight spectra of ions are performed. A multi population of electrons is formed as the laser interaction with plasma proceeds. Ions accelerated by hot electrons to MeV energy are emitted in bursts. The neutron yield from the deuterated target is compared to yields obtained from other experiments. Constraint of non-linear processes on the ion acceleration and resulting neutron yields is shown.

Laser-Target Experiments at PALS for Deuterium Plasma Beam Fusion

  • DOI: 10.12693/APhysPolA.138.579
  • Odkaz: https://doi.org/10.12693/APhysPolA.138.579
  • Pracoviště: Katedra fyziky
  • Anotace:
    The Prague Asterix Laser System (PALS) is a terawatt iodine laser (1.2 kJ, 350 ps, 1315 nm), designed to deliver irradiance on target of about 3 x 10(16) W/cm(2). The PALS laser together with a Ti:sapphire laser (1 J, 50 fs, 800 nm) is used for experiments allowing femtosecond probing of laser-produced plasma. We present an experimental study of emission of hot electrons, fast ions and fusion neutrons generated through the H-2(d;n)He-3 fusion reaction of deuterons. During the laser-plasma interaction and plasma expansion, a multi-population of electrons appears. Non-isotropic emission of fast as well as thermal electrons is typical for the interaction of nanosecond laser radiation with plasma. The production of relativistic electrons makes it possible to accelerate protons to MeV energy and generate fusion neutrons via fusion reactions. The DD-neutron yield is compared to yields obtained from other experiments. Depending on the energy of the laser pulse, it is shown that the competition of laser contrast and laser pulse intensity sets a fundamental constraint on the ion emission and the resultant neutron yield performance of deuterated targets.

Neutron fluence distribution in experiments with 3 MA deuterium gas-puff z-pinch

  • DOI: 10.1063/5.0008108
  • Odkaz: https://doi.org/10.1063/5.0008108
  • Pracoviště: Katedra fyziky
  • Anotace:
    Deuterium gas-puff z-pinches are very efficient laboratory sources of neutron pulses. Using a novel hybrid gas-puff load on the GIT-12 generator, a significant increase in the neutron yields up to

Production of energetic protons, deuterons, and neutrons up to 60 MeV via disruption of a current-carrying plasma column at 3 MA

  • DOI: 10.1088/1367-2630/abbab5
  • Odkaz: https://doi.org/10.1088/1367-2630/abbab5
  • Pracoviště: Katedra fyziky
  • Anotace:
    Acceleration of ions to multi-MeV energies is investigated in various plasma devices to better understand processes in astrophysical plasmas and to develop efficient accelerators for a variety of applications. This paper reports the production of proton, deuteron, and electron beams in a z-pinch-a cylindrically symmetric plasma column that is compressed by its own magnetic field. For this work, the GIT-12 pulsed-power generator was used to drive a novel configuration of z-pinch that dramatically enhanced ion acceleration associated with disruption of the current by instabilities in the compressed plasma. During the disruption of 3 MA current, hydrogen ions were accelerated up to at least 50 MeV, which is almost a hundred-times the ion energy provided by the generator driving voltage of 0.6 MV. Under optimal conditions, the total numbers of hydrogen ions with energies above 20 and 50 MeV were 4 x 10(13)and 10(11), respectively. Accelerated deuterons produced one 20 ns (full width at half maximum) pulse of fast neutrons via D(d, n)He-3 and other nuclear reactions. A maximum neutron output of (1.0 +/- 0.2) x 10(12)neutrons/sr was observed downstream, i.e., in the anode to cathode direction. In this direction, the maximum neutron energy reached 58 +/- 7 MeV. Both ion and neutron beams in our experiment reached an end-point energy of about 60 MeV, which is the highest value observed in pulsed-power devices. A localized peak voltage of greater than or similar to 60 MV was driven by the inductive energy that was stored around the plasma column and that was extracted during a sub-nanosecond current drop. Considering the natural occurrence of current-carrying columns in laboratory and space plasmas, the current interruption observed in z-pinches could represent a more general physical process that contributes to the efficient conversion of magnetic energy into the energy of particle beams in various plasmas.

Scenario of a magnetic dynamo and magnetic reconnection in a plasma focus discharge

  • DOI: 10.1063/1.5133103
  • Odkaz: https://doi.org/10.1063/1.5133103
  • Pracoviště: Katedra fyziky
  • Anotace:
    The paper discusses a possible energy transformation that leads to the acceleration of fast ions and electrons. In plasma-focus discharges that occur during deuteriumfilling, which have a maximum current of about 1MA, the accelerated deuterons producefastfusion neutrons andfast electrons hard X-ray emissions. Their total energy, which is of the order of several kilojoules, can be delivered by the discharge through a magnetic dynamo and selforganization to the ordered plasma structures that are formed in a pinch during the several hundreds of nanoseconds of the pinch implosion, stagnation, and evolution of instabilities. This energy is finally released during the decay of the ordered plasma structures in the volume between the anode face and the umbrella front of the plasma and current sheath in the form of induced electric fields that accelerate fast electrons and ions.

Spatial distribution of ion emission in gas-puff z-pinches and dense plasma foci

  • DOI: 10.1088/1361-6587/ab6902
  • Odkaz: https://doi.org/10.1088/1361-6587/ab6902
  • Pracoviště: Katedra fyziky
  • Anotace:
    Mega-ampere dense plasma foci and deuterium gas-puff z-pinches can accelerate deuterons to multi-MeV energies. Diagnostic measurements of the properties of these ions provide information about ion acceleration in z-pinch plasmas. In particular, the results from ion pinhole cameras seem to be useful for the discussion of ion acceleration mechanisms. Recently, we have used various configurations of ion pinhole cameras in deuterium gas-puff experiments on the GIT-12 generator at the Institute of High Current Electronics in Tomsk and on the HAWK generator at the US Naval Research Laboratory in Washington. The stack of radiochromic films and CR-39 solid-state nuclear track detectors recorded deuterons with energies up to 30 MeV. From our ion diagnostics, we obtained the spatial distribution of the ion source and the ion-beam divergence during the ion emission. This ion-beam divergence was found to decrease with increasing deuteron energy. At 20 MeV, the divergence of each of the individual micro-beams that composed the ion source was on the order of 10 mrad. The deflection of each micro-beam due to the azimuthal magnetic and/or radial electric fields resulted in radial stripes observed by the beam-profile detectors. By analyzing the ion pinhole images, we found that the deuterons were emitted both from a central spot and from a ring-shaped region with a rather large diameter, on the order of 1 cm. The origin and particular diameter of this ring is attributed to the geometry of the electrodes and to the distribution of the current density before the disruption.

Acceleration of protons and deuterons up to 35 MeV and generation of 10(13) neutrons in a megaampere deuterium gas-puff z-pinch

  • DOI: 10.1088/1361-6587/aadc99
  • Odkaz: https://doi.org/10.1088/1361-6587/aadc99
  • Pracoviště: Katedra fyziky
  • Anotace:
    The acceleration of hydrogen ions up to 35 MeV is observed in the z-pinch experiments on the GIT-12 generator at a 3 MA current and 0.6 MV driving voltage. High ion energies are obtained with a novel configuration of a deuterium gas-puff z-pinch. In this configuration, a hollow cylindrical plasma shell is injected around an inner deuterium gas puff to form a homogeneous, uniformly conducting layer between electrodes at the initial phase of z-pinch implosion. The stable implosion at the velocity up to 650 km s(-1) is important to deliver more current onto the z-pinch axis. Magnetohydrodynamic instabilities become apparent first at stagnation. After the disruptive development of m = 0 instabilities, similar to 20 ns pulses of high-energy photons, neutrons, electrons, and ions are observed. The average neutron yield is 2 x 10(12). The ion emission is characterized by various diagnostic techniques including those based on the usage of neutron-producing samples. When a large neutron-producing sample is placed onto the axis below a cathode mesh, the neutron yield is increased up to (1.1 +/- 0.3) x 10(13). Considering a similar to 130 kJ energy input into z-pinch plasmas and magnetic field, this implies the neutron production efficiency of similar to 10(8) neutrons per one Joule of the z-pinch energy.

Comprehensive diagnostics of hot electron emission from plasmas produced by sub-nanosecond terawatt laser on thin foil metal targets

  • DOI: 10.1088/1748-0221/14/12/C12003
  • Odkaz: https://doi.org/10.1088/1748-0221/14/12/C12003
  • Pracoviště: Katedra fyziky
  • Anotace:
    Interaction of high-power and high-energy lasers with matter generates plasmas emitting considerable amounts of relativistic electrons. In this contribution such plasmas were produced by PALS kJ laser facility delivering the beam with intensity of the order of 3 . 10(16)W . cm(-2) in 400 ps on thin foil metal targets. To study the emission of hot electrons in horizontal plane around the target, an array of electron spectrometers was employed to record the electron emission from the plasma in several angles around the target. For experimental determination of the total number of hot electrons escaping from the plasma through the plasma barrier a target probe was used in order to measure the target return current which neutralizes the positive target charge produced by these escaping hot electrons. Together with this diagnostics the femtosecond interferometry was used to obtain spatial electron density profiles in close proximity to the irradiated target at selected time delays. Interferograms indicated occurrence of plasma density modulations in front of the target and made it possible to calculate the number of electrons contained within thermal fraction of the plasma produced by the laser. The number of these electrons correlates with the flux of soft x-ray radiation observed with the use of an x-ray streak camera.

Evolution of a Pinch Column During the Acceleration of Fast Electrons and Deuterons in a Plasma-Focus Discharge

  • DOI: 10.1109/TPS.2018.2874288
  • Odkaz: https://doi.org/10.1109/TPS.2018.2874288
  • Pracoviště: Katedra fyziky
  • Anotace:
    Plasma in a pinch column, as produced by a plasma-focus discharge at the deuterium filling and the current intensity reaching 1 MA, was investigated at the total neutron yield reaching about 1010 per discharge. The use was made of neutron diagnostics, laser interferometry, soft X-ray measurements, optical emission spectroscopy, magnetic probes, as well as electron and ion measurements with the temporal, spatial, and energetic resolutions. The detailed studies showed the ordered toroidal, helical, and plasmoidal structures which could contain currents with poloidal and toroidal components and their associated magnetic fields. Their spontaneous transformations were explained by changes in a topology of magnetic field lines due to magnetic reconnections. A nonthermal acceleration of fast electrons and ions (producing hard X-rays and fusion neutrons, respectively) corresponded to: 1) the formation of plasmoids in the pinch column and 2) a decay of pinch constrictions and secondary plasmoids during the evolution of instabilities. A filamentary structure of the current flow could explain the high energy density and fast transformations of the magnetic energy into kinetic energy of electron and ion beams (reaching energy of hundreds of kiloelectronvolt). This paper summarizes the results obtained with the PF-1000 facility in 2009–2017, and describes the internal transformations in a dense plasma column during the evolution of MHD instabilities.

Evolution of the Pinched Column During Hard X-ray and Neutron Emission in a Dense Plasma Focus

  • DOI: 10.1007/s10894-018-0194-x
  • Odkaz: https://doi.org/10.1007/s10894-018-0194-x
  • Pracoviště: Katedra fyziky
  • Anotace:
    The paper summarizes important results of the recent experimental studies performed on the plasma-focus PF-1000 facility operated in Warsaw, Poland, mainly with the pure deuterium filling. Attention is focused on the evolution of toroidal and plasmoidal self-organized structures formed by internal closed currents inside the dense plasma column. The production of hard x-rays and neutrons corresponds with the formation and decay of plasmoids, in which charged particles can be accelerated effectively to high energies, during a release of the magnetic energy from current filaments of high energy density. It is noticed that the studies of laboratory fusion and cosmic plasmas deal with similar problems, e.g., the fast release of the magnetic energy in a form of high-energy charged particle beams.

Features of fast deuterons emitted from plasma focus discharges

  • DOI: 10.1063/1.5080974
  • Odkaz: https://doi.org/10.1063/1.5080974
  • Pracoviště: Katedra fyziky
  • Anotace:
    This paper presents the discussion concerning the characteristics of the fast deuterons which have energy above 30 keV and are recorded during high-current plasma-focus (PF) discharges, by means of PM-355 plastic track-detectors placed inside ion pinhole cameras. The fast deuterons evoke D-D fusion reactions, mainly by a beam-target mechanism. The distribution of the magnetic field, which influences the trajectories of the recorded deuterons, is discussed. It is found that the fast deuterons are produced in various local sources and their motion is strongly influenced by a circular symmetry of the local magnetic field, which increases their radial shift with a decrease in their energy. The sources of these deuterons are probably located inside the plasmoids and in some local regions of the ring-shaped plasma structures. These ring-structures can be formed outside the dense pinch column, up to a radius of 5 cm. Global magnetic fields, associated with the total current flow in the PF discharge, have a weaker influence. The observed radial shift of the recorded fast deuterons is interpreted as a result of their deflection by magnetic fields which have opposite orientations of the azimuthal components, associated with the currents flowing in directions towards and from the applied ion detectors. The local sources of the recorded fast deuterons correspond to filamentary structures, in which the stored magnetic energy (having the local high density) can be released in induced electric fields accelerating the deuterons during the magnetic reconnections.

Influence of an external additional magnetic field on the formation of a plasma column in a dense plasma focus

  • DOI: 10.1063/1.5094568
  • Odkaz: https://doi.org/10.1063/1.5094568
  • Pracoviště: Katedra fyziky
  • Anotace:
    This paper concerns the evolution of internal structures and the neutron production in plasma-focus discharges performed in the presence of a permanent magnet (placed inside the anode front) and within a residual magnetic field (after the removal of this magnet). The initial magnetic field generated by this magnet prevented: (i) the effective compression of a dense pinch column, (ii) the formation of plasma organized structures, and (iii) the evolution of plasma instabilities. The experimental results have shown an increase in the initial magnetic field due to a magnetic dynamo effect in the presence of the permanent magnet, as well as in a series of shots performed after its removal. It was observed that the appearance of plasmoidal structures is necessary for the emission of fusion neutrons. A characteristic quasicylindrical plasma layer of the radius corresponding to the plasma lobule tops, which might be identified with a ring region of the acceleration of fast deuterons, was also observed.

Initial conditions in the hawk dense plasma focus

  • DOI: 10.1109/PPPS34859.2019.9009625
  • Odkaz: https://doi.org/10.1109/PPPS34859.2019.9009625
  • Pracoviště: Katedra fyziky
  • Anotace:
    The 670 kA Hawk pulsed power generator at NRL has been configured as a fast (1.2 μs rise time), high inductance (607 nH) driver for a dynamic dense plasma focus (DPF) load in order to create a testbed for the study of charged particle acceleration mechanisms in imploding plasmas. The current pulse is initiated in a deuterium plasma injected radially by three Marshall guns. This plasma is accelerated through a coaxial region, and pinches onto neutral deuterium injected axially by a gas-puff valve. Promising experimental results along with recent improvements to the Marshall gun design have prompted efforts to better characterize the density profiles produced by the guns. A multichannel heterodyne interferometer focused into a ribbon beam is used to provide time-resolved measurements of the Marshall gun plasma density, allowing parameters to be tuned and mass distributions to be established for a wide range of initial conditions. These interferometric measurements are used in establishing a standard operating condition for the experiment in a high neutron yield regime.

Target return current in low-intensity laser target interaction

  • DOI: 10.1117/12.2522511
  • Odkaz: https://doi.org/10.1117/12.2522511
  • Pracoviště: Katedra fyziky
  • Anotace:
    Laser-target interaction experiments demonstrated that the return target current, j(TC)(t), which neutralizes the target charge appearing when the fastest electrons escape the plasma, is one of principal characteristics of the laser-matter interaction. j(TC)(t) flowing between the target and the ground is emerging just when the laser intensity exceeds the threshold intensity of the plasma formation. The experimental determination of the number of escaped electrons is primarily based on precise target current observations.

Axial compression of plasma structures in a plasma focus discharge

  • DOI: 10.1063/1.5033997
  • Odkaz: https://doi.org/10.1063/1.5033997
  • Pracoviště: Katedra fyziky
  • Anotace:
    The paper describes the behaviour of plasma within a MA plasma-focus with a novel electrode configuration, in which the anode and anti-anode were both equipped with conical tips. This configuration was applied to test the possibility of reducing the pinch axial dimensions during the radial compression of a current sheath. It made it possible to strengthen a dense plasma jet near the anode end, which ejected plasma into a bigger plasmoidal structure formed in the central pinch region. It did not allow forming an opposite anti-anode jet and stopped the axial motion of this structure. In plasma focus discharges with the deuterium filling, the decay of the anode jet and the corresponding plasmoid evolution were accompanied by the fusion-neutron production. Some results obtained with this configuration have also supported the hypothesis of the acceleration of fast electrons and ions at a release of the magnetic energy during magnetic reconnections in the organized dense plasma structures.

Characterization of fast deuterons involved in the production of fusion neutrons in a dense plasma focus

  • DOI: 10.1063/1.5012021
  • Odkaz: https://doi.org/10.1063/1.5012021
  • Pracoviště: Katedra fyziky
  • Anotace:
    This paper considers regions of a fast deuteron production in a correlation with an evolution of ordered structures inside a pinch column of a mega-ampere plasma focus discharge. Ion pinhole cameras equipped with plastic PM-355 track-detectors recorded fast deuterons escaping in the downstream and other directions (up to 60 to the z-axis). Time-integrated ion images made it possible to estimate sources of the deuteron acceleration at the known magnetic field and deuteron energy values. The images of the fast deuterons emitted in the solid angle ranging from 0 to 4 showed two forms: central spots and circular images. The spots of 1–2 cm in diameter were produced by deuterons from the central pinch regions. The circular-shaped images of a radius above 3 cm (or their parts) were formed by deuterons from the region surrounding the dense pinch column. The ion pinhole cameras placed at angles above 20 to the z-axis recorded the ion spots only, and the ring-images were missing. The central region of the deuteron acceleration could be associated mainly with plasmoids, and the circular images could be connected with ring-shaped regions of the radius corresponding to tops of the plasma lobules outside the dense pinch column. The deuteron tracks forming ring-shaped images of a smaller (0.5–1) cm radius could be produced by deflections of the fast deuterons, which were caused by a magnetic field inside the dense pinch column.

Investigation of Magnetic Fields in Z-Pinches via Multi-MeV Proton Deflectometry

  • DOI: 10.1109/TPS.2018.2874207
  • Odkaz: https://doi.org/10.1109/TPS.2018.2874207
  • Pracoviště: Katedra fyziky
  • Anotace:
    Proton deflectometry is a promising way for mapping electric and magnetic fields in high-density and high-temperature plasmas, where an application of the classical methods (B-dot probes, Faraday rotation, and Zeeman splitting) is limited. It is based on the detection of a multi-MeV proton beam deflected in examined B-fields. In the past years, it has been successfully utilized in laser-generated plasmas for E-field and B-field measurements. Using our numerical code, we investigate the capabilities of proton deflectometry as a diagnostic method of MA Z-pinches. We simulate proton trajectories propagating through typical Z-pinch B-fields in two fundamental experimental setups (radial and axial) in order to study synthetic images (deflectograms). We demonstrate where proton deflectometry might be beneficial for the Z-pinch research. We explain a formation of the key features of deflectograms, which give us information about a profile and strength of the Z-pinch B-fields. We introduce a BL parameter, denoting an effective B-field averaged along the deflected proton orbit and show its importance for the proton deflectometry.

Ion acceleration mechanism in mega-ampere gas-puff z-pinches

  • DOI: 10.1088/1367-2630/aac545
  • Odkaz: https://doi.org/10.1088/1367-2630/aac545
  • Pracoviště: Katedra fyziky
  • Anotace:
    Acceleration of high energy ions was observed in z-pinches and dense plasma foci as early as the 1950s. Even though many theories have been suggested, the ion acceleration mechanism remains a source of controversy. Recently, the experiments on the GIT-12 generator demonstrated acceleration of ions up to 30 MeV from a deuterium gas-puff z-pinch. High deuteron energies enable us to obtain unique information about spatial, spectral and temporal properties of accelerated ions. In particular, the off-axis ion emission from concentric circles of a similar to 1 cm diameter and the radial lines in an ion beam profile are germane for the discussion of acceleration mechanisms. The acceleration of 30 MeV deuterons can be explained by the fast increase of an impedance with a sub-nanosecond e-folding time. The high (> 10 Omega) impedance is attributed to a space-charge limited flow after the effective ejection of plasmas from m = 0 constrictions. Detailed knowledge of the ion acceleration mechanism is used with a neutron-producing catcher to increase neutron yields above 10^13 at a current. of. 2.7 MA.

Magnetized plasma implosion in a snail target driven by a moderate intensity laser pulse

  • DOI: 10.1038/s41598-018-36176-8
  • Odkaz: https://doi.org/10.1038/s41598-018-36176-8
  • Pracoviště: Katedra fyziky
  • Anotace:
    Optical generation of compact magnetized plasma structures is studied in the moderate intensity domain. A sub-ns laser beam irradiated snail-shaped targets with the intensity of about 10(16) W/cm(2). With a neat optical diagnostics, a sub-megagauss magnetized plasmoid is traced inside the target. On the observed hydrodynamic time scale, the hot plasma formation achieves a theta-pinch-like density and magnetic field distribution, which implodes into the target interior. This simple and elegant plasma magnetization scheme in the moderate-intensity domain is of particular interest for fundamental astrophysical-related studies and for development of future technologies.

Production of relativistic electrons, MeV deuterons and protons by sub-nanosecond terawatt laser

  • DOI: 10.1063/1.5052146
  • Odkaz: https://doi.org/10.1063/1.5052146
  • Pracoviště: Katedra fyziky
  • Anotace:
    By the use of various experimental techniques, it is shown that the relativistic electrons, MeV protons, and deuterons are emitted from a 500-mu m thick (CD2)(n) target exposed to I lambda(2) approximate to 5 x 10(16)W cm(-2) mu m(2), which is delivered by the iodine photodissociation laser Prague Asterix Laser System. A parameter reflecting the laser-power efficiency of the proton acceleration is used for comparison of the observed maximum proton energy with data from other experiments. The number of protons and deuterons constituting the backward and forward jets is estimated. Values of maximum proton energies and electron temperatures indicate that the laser intensity should reach a relativistic level through the laser beam self-focusing. The occurrence of electron bunches in front of the irradiated target surface was identified by time resolved femtosecond interferometry. Energy distribution functions of electrons emitted in the both backward and forward directions are analysed and compared. Published by AIP Publishing.

Target current: An appropriate parameter for characterizing the dynamics of laser-matter interaction

  • DOI: 10.1117/12.2520177
  • Odkaz: https://doi.org/10.1117/12.2520177
  • Pracoviště: Katedra fyziky
  • Anotace:
    A resistive target probes were employed to obtain unique characteristics of the dynamic of the laser-matter interaction through the observation of a return current neutralizing the positive target charge caused by electrons definitely leaving the plasma. Experimental observations show that three phases of the laser-produced plasma are well recognized, i.e. the plasma ignition phase, active plasma phase, and afterglow phase already for the lowest laser intensity at the focal point of 108 Wcm-2 . Then, at higher intensities the first two phases strongly dominate and the target current reaches a value of 10 kA. A throughput of plasma barrier for the fastest electrons leaving the plasma is defined, and its value is experimentally estimated. We also present key experiments proving that the duration of the electrical charge on the target is much longer than the duration of the laser-plasma interaction for the entire intensity range.

Experimental research of neutron yield and spectrum from deuterium gas-puff z-pinch on the GIT-12 generator at current above 2 MA

  • DOI: 10.1088/1742-6596/830/1/012017
  • Odkaz: https://doi.org/10.1088/1742-6596/830/1/012017
  • Pracoviště: Katedra fyziky
  • Anotace:
    The Z-pinch experiments with deuterium gas-puff surrounded by an outer plasma shell were carried out on the GIT-12 generator (Tomsk, Russia) at currents of 2 MA. The plasma shell consisting of hydrogen and carbon ions was formed by 48 plasma guns. The deuterium gas-puff was created by a fast electromagnetic valve. This configuration provides an efficient mode of the neutron production in DD reaction, and the neutron yield reaches a value above 10^12 neutrons per shot. Neutron diagnostics included scintillation TOF detectors for determination of the neutron energy spectrum, bubble detectors BD-PND, a silver activation detector, and several activation samples for determination of the neutron yield analysed by a Sodium Iodide (NaI) and a high-purity Germanium (HPGe) detectors. Using this neutron diagnostic complex, we measured the total neutron yield and amount of high-energy neutrons.

Filamentation in the pinched column of the dense plasma focus

  • DOI: 10.1063/1.4978558
  • Odkaz: https://doi.org/10.1063/1.4978558
  • Pracoviště: Katedra fyziky
  • Anotace:
    The paper describes the filamentary structure observed in the high-energy ultraviolet radiation for discharges performed at the hydrogen- or deuterium-filling and at the puffing of hydrogen, deuterium or helium, in a mega-ampere dense plasma-focus facility. The lifetime of this structure overcomes 50ns. These filaments connect the surface of a pinched column with internal plasmoids formed at different combinations of filling and puffing gases and they should transport some current and plasma. During all the investigated deuterium shots, the fusion-produced neutrons were recorded. Therefore, deuterons should be present in the region of their acceleration, independent of the applied puffing of the gas. Simultaneously with the observed filaments, inside the dense plasma column small plasma-balls of mm-dimensions were observed, which had a similar lifetime (longer than the relaxation time) and quasi-stationary positions in the discharge volume. The observed filaments and balls might be a manifestation of the (i) discrete spatial structure of the current flowing through and around the dense plasma column and (ii) transport of the plasma from external layers to the central region. Their formation and visualization were easier due to the application of air admixtures in the puffed gas. Published by AIP Publishing.

Increase in the neutron yield from a dense plasma-focus experiment performed with a conical tip placed in the centre of the anode end

  • DOI: 10.1063/1.4994097
  • Odkaz: https://doi.org/10.1063/1.4994097
  • Pracoviště: Katedra fyziky
  • Anotace:
    The paper describes the evolution of self-organized structures inside a pinched plasma column during the phase of the effective production of fusion neutrons, as observed in the mega-ampere plasma focus experiment performed with a conical tip placed in the centre of the anode face. In a comparison with the plane anode face configuration, the described anode shape facilitated transformations in the pinch column during the neutron production and increased the neutron yield several times. Simultaneously, it decreased the minimal diameter and the length of the pinched column, and it depressed the first neutron pulse. It also induced shorter pulses of X-rays and neutrons, which enabled the determination of a temporal difference between the emission of electron and deuteron beams. The fast electrons were produced mainly during a disruption of the pinch constriction, while the fast deuterons – during the formation and explosion of plasmoids. The paper also presents the temporal evolution of a current distribution in the plasmoid during the neutron production, as well as the appearance and stable positions of current filaments traces upon the surface of the conical anode tip.

Neutron Spectrum Measured by Activation Diagnostics in Deuterium Gas-Puff Experiments on the 3 MA GIT-12 Z-Pinch

  • DOI: 10.1109/TPS.2017.2763641
  • Odkaz: https://doi.org/10.1109/TPS.2017.2763641
  • Pracoviště: Katedra fyziky
  • Anotace:
    A set of neutron diagnostics including scintillation time-of-flight detectors, bubble detectors, and several kinds of threshold nuclear activation samples is used to obtain information about the yield and spectrum of the neutrons produced by a deuterium gas-puff z-pinch. The experiments are performed at a current of about 3 MA on the GIT-12 generator at the Institute of High Current Electronics of the Siberian Branch of Russian Academy of Sciences in Tomsk. The average neutron yield in the experiments in 2016 was 2.3 x 10¹² neutrons per single shot. Using the data obtained with the help of neutron activation diagnostics, the time-of-flight detectors have been absolutely calibrated and the broad energy spectrum of the produced neutrons was evaluated. By the calculations presented in this paper, due to the multi-MeV energies of deuterons generated in the pinch, up to 15% of the total neutron yield could be produced by nuclear reactions of deuterons with a stainless steel vacuum chamber and aluminum components of the diagnostic apparatus inside the chamber.

Phases of plasma produced with nanosecond laser

  • Pracoviště: Katedra fyziky
  • Anotace:
    Recent experimental studies have shown that the current balancing the charge occurred on a target irradiated with a laser can be used as a basic parameter for characterization of laser ablation. The time-resolved target current indicates the occurrence of various phases of the laser-produced plasma. During the first plasma phase defined by the duration of laser-target interaction, the time derivative of the target current matches the time-resolved laser intensity. The second phase of the laser-produced plasma starts after termination of the laser-matter interaction. For the entire duration of this active phase, the plasma surviving on the target surface emits transient electromagnetic radiation (EMP), X-ray radiation, and slow ions. This surface plasma causes the target charging balanced by a return target current on a time scale of 100 ns. Then the target holder acts as a probe, the signal of which can indicate a residual plasma persisting inside the target chamber on a time scale of microseconds.

Spectral and temporal characteristics of target current and electromagnetic pulse induced by nanosecond laser ablation

  • DOI: 10.1088/1361-6587/aa6805
  • Odkaz: https://doi.org/10.1088/1361-6587/aa6805
  • Pracoviště: Katedra fyziky
  • Anotace:
    The current balancing the target charging and the emission of transient electromagnetic pulses (EMP) driven by the interaction of a focused 1.315 mu m iodine 300 ps PALS laser with metallic and plastic targets were measured with the use of inductive probes. It is experimentally proven that the duration of return target currents and EMPs is much longer than the duration of laser-target interaction. The laser-produced plasma is active after the laser-target interaction. During this phase, the target acts as a virtual cathode and the plasma-target interface expands. A double exponential function is used in order to obtain the temporal characteristics of EMP. The rise time of EMPs fluctuates in the range up to a few tens of nanoseconds. Frequency spectra of EMP and target currents are modified by resonant frequencies of the interaction chamber.

Target current: a useful parameter for characterizing laser ablation

  • DOI: 10.1017/S0263034617000040
  • Odkaz: https://doi.org/10.1017/S0263034617000040
  • Pracoviště: Katedra fyziky
  • Anotace:
    A current flowing between the ground and target exposed to the nanosecond laser radiation is analyzed to complete characteristics of laser ablation. Three phases of the target current are distinguished. During the ignition phase, the electron emission is driven by the laser pulse and the positive charge generated on the target is balanced by electrons coming from the ground through the target holder. At post-pulse times, a peaked waveform of the target current is typical for the active phase of the plasma and can give information on the material composition of the ablated surface layers. The afterglow phase is determined by a current of electrons flowing from the target to the ground. Experiment shows that the time-resolved target current is very sensitive to the actual composition of the surface layer of irradiated target and laser parameters.

Transformation of the ordered internal structures during the acceleration of fast charged particles in a dense plasma focus

  • DOI: 10.1063/1.4991384
  • Odkaz: https://doi.org/10.1063/1.4991384
  • Pracoviště: Katedra fyziky
  • Anotace:
    The paper concerns important differences in the evolution of plasma column structures during the production of fusion neutrons in the first and subsequent neutron pulses, as observed for plasma focus discharges performed with the deuterium filling. The first neutron pulse, of a more isotropic distribution, is usually produced during the formation of the first big plasmoid. The next neutron pulses can be generated by the fast deuterons moving dominantly in the downstream direction, at the instants of a disruption of the pinch constriction, when other plasmoids are formed during the constriction evolution. In both cases, the fusion neutrons are produced by a beam-target mechanism, and the acceleration of fast electron- and deuteron-beams can be interpreted by transformation and decay of the magnetic field associated with a filamentary structure of the current flow in the plasmoid.

Deuterium z-pinch as a powerful source of multi-MeV ions and neutrons for advanced applications

  • DOI: 10.1063/1.4942944
  • Odkaz: https://doi.org/10.1063/1.4942944
  • Pracoviště: Katedra fyziky
  • Anotace:
    A novel configuration of a deuterium z-pinch has been used to generate a nanosecond pulse of fast ions and neutrons. At a 3 MA current, the peak neutron yield of (3.6 +/- 0.5) x 10(12) was emitted within 20 ns implying the production rate of 10 20 neutrons/s. High neutron yields resulted from the magnetization of MeV deuterons inside plasmas. Whereas deuterons were trapped in the radial direction, a lot of fast ions escaped the z-pinch along the z-axis. A large number of >25MeV ions were emitted into a 250 mrad cone. The cut-off energy of broad energy spectra of hydrogen ions approached 40 MeV. The total number of >1 MeV and >25 MeV deuterons were 10(16) and 10(13), respectively. Utilizing these ions offers a real possibility of various applications, including the increase of neutron yields or the production of short-lived isotopes in samples placed in ion paths. On the basis of our experiments with various samples, we concluded that a single shot would have been sufficient to obtain GBq positron activity of 13 N isotopes via the C-12(d, n)(13) N reaction. Furthermore, the first z-pinch generated neutron radiograph produced by approximate to 20 ns pulses is presented in this paper. (C) 2016 AIP Publishing LLC.

Evolution of the small ball-like structures in the plasma focus discharge

  • DOI: 10.1515/nuka-2016-0027
  • Odkaz: https://doi.org/10.1515/nuka-2016-0027
  • Pracoviště: Katedra fyziky
  • Anotace:
    The experiments were carried out in the PF-1000 plasma-focus device at the maximum current reaching about 2 MA, at the deuterium or neon filling and with deuterium injected from a gas-puff nozzle placed on the axis of the anode face. Ball-like structures of diameters of 1-12 mm were identified in interferometric and XUV pinhole camera frames. We made the statistical description of their parameters. A lifetime of the ball-like structures was in the range from 30 to 210 ns, and in some cases even more. These structures appeared mostly at the surface of the imploding plasma shell and they did not change their position in relation to the anode end. During the evolution of these structures, interferometric fringes were observed near the surfaces of the structures only, and their internal parts were initially chaotic (without noticeable) fringes. Subsequently the number of interferometric fringes increased (the internal 'chaotic' area was filled with fringes too) and later on it decreased. The radii of the ball-like structures were mostly increasing during their existence. The maximum electron density reached the value of 10(24) to 10(25) m(-3). The ball-like structures decayed by absorption inside the expanded pinch column and/or gradually expired in rare plasma outside of the dense plasma column.

Generation of fast neutrons through deuteron acceleration at the PALS laser facility

  • DOI: 10.1088/1748-0221/11/03/C03050
  • Odkaz: https://doi.org/10.1088/1748-0221/11/03/C03050
  • Pracoviště: Katedra fyziky
  • Anotace:
    Recent experiments at the laser facility PALS focused on the laser driven fusion of deuterons are reviewed. They benefit of high reaction cross-sections and of a high number of multi-MeV deuterons from thick CD2 targets irradiated by intensity of 3x10(16) W cm(2). In the reported experiments fast fusion neutrons with energy up to 16 MeV were produced through Li-7(d, n)Be-8 and B-11(d, n)C-12 reactions in a pitcher-catcher target configuration. When using a large area CD2 foil as a secondary catcher target the total maximum neutron yield from the H-2(d, n)He-3 reaction increased by a factor of about 5, from 4x10(8) to 2x10(9). This result reveals that most of the deuterons having enough kinetic energy to enter a fusion reaction are emitted from the primary target into vacuum.

Influence of the Al wire placed in the anode axis on the transformation of the deuterium plasma column in the plasma focus discharge

  • DOI: 10.1063/1.4953569
  • Odkaz: https://doi.org/10.1063/1.4953569
  • Pracoviště: Katedra fyziky
  • Anotace:
    In this paper, we describe the influence of an Al wire of 270 lm in diameter placed along the anode axis on the transformation of the deuterium pinch column in a megaampere (MA) plasma focus device. The evolution of the pinched column and of the wire corona was investigated by means of the multiframe interferometry, neutron and X-ray diagnostics. The wire corona did not influence considerably on the evolution of dense plasma structures and neutron production, but it increased the plasma density and consequently, the currents around its surface. The distribution of the closed internal currents (ranging hundreds of kA) and associated magnetic fields amounting to 5 T were also estimated in the dense plasma column and in plasmoidal structures at the near-equilibrium state. The description is based on the balance of the plasma pressure and the pressure of the internal poloidal and toroidal current components compressed by the external pinched column. The dominant number of fusion deuterium-deuterium (D-D) neutrons is produced during the evolution of instabilities, when theuninterrupted wire corona (containing deuterium) connects the dense structures of the pinch, and it did not allow the formation of a constriction of the sub-millimeter diameter.

Interferometry and x-ray diagnostics of pinched helium plasma in a dense plasma focus with an Al-wire on the axis

  • DOI: 10.1063/1.4968227
  • Odkaz: https://doi.org/10.1063/1.4968227
  • Pracoviště: Katedra fyziky
  • Anotace:
    The paper describes the evolution of the ordered dense toroidal- and plasmoidal-like structures in a pinch column and the hard X-ray emission from mega-ampere dense plasma-focus discharges performed at the helium (He) filling. Some shots were carried out with an Al-wire of 270 lm in diameter, which was placed along the z-axis in the front of the anode face. The evolution of the considered structures was investigated by means of a multi-frame laser interferometer system as well as the X-ray diagnostics, and it was compared with their evolution observed earlier at the deuterium (D2) filling. In He-plasma, the ions had a higher mass and Z-number, and at the same initial filling pressure, the velocity of plasma transformations was decreased, but the stability of the investigated structures, as well as the self-generated azimuthal current component and the soft X-ray radiation were increased. The distribution of the plasma electron density (determined from the interferometric images) made it possible to estimate closed currents during the quasi-stationary phases. It was found that the internal toroidal- and plasmoidal-currents reached the level of hundreds of kA. The plasma corona around the Al-wire (penetrating through the internal structures) impeded the formation of a small diameter of the pinch constriction, but it did not prevent the production of fast electron beams with energies above 100 keV, similar to those observed at the D2-filling.

Magnetic field induced by laser-driven target current

  • Pracoviště: Katedra fyziky
  • Anotace:
    This contribution deals with direct observation of a transient magnetic field induced by a current flowing through the target holder to balance the target charging caused by intense laser radiation delivered by the 3 TW, 300 ps laser system PALS. Both the target and its holder fixed to the interaction chamber react to the target ablation as an electrical circuit, which emits electromagnetic pulses in the megahertz to gigahertz domain. For this reason the interaction chamber is considered as a resonant cavity in which different modes of EM field oscillate for hundreds of nanoseconds until EM waves are completely lost. We present an inductive target probe developed by Cikhardt et al. Rev. Sci. Instrum. 85 (2014) 103507, allowing the direct observation of the transient target current. Since the applied inductive target probe is resistive against the interfering electromagnetic pulse (EMP) occurred inside the interaction chamber where the charged particles are accelerated, the relationship between the magnetic part of the EMP elsewhere inside and outside the interaction chamber and the magnetic field induced by the neutralization target current can be obtained. Frequency analysis indicates a multimode frequency distribution of EMP spectra which arises as a mixture of large number of modes.

The evolution of the plasmoidal structure in the pinched column in plasma focus discharge

  • DOI: 10.1088/0741-3335/58/4/045005
  • Odkaz: https://doi.org/10.1088/0741-3335/58/4/045005
  • Pracoviště: Katedra fyziky
  • Anotace:
    In this paper, a description is provided of the evolution of the dense spherical-like structures— plasmoids—formed in the pinched column of the dense plasma focus at the current of 1 MA at the final phase of implosion of the deuterium plasma sheath and at the phase of evolution of instabilities both at the time of HXR and neutron production. At the stratification of the plasma column, the plasma injected to the dense structures from the axially neighboring regions forms small turbulences which increase first the toroidal structures, and finally generates a nonchaotic current plasmoidal structure with central maximal density. This spontaneous evolution supports the hypothesis of the spheromak-like model of the plasmoid and its sub-millimeter analogy, high-energy spot. These spots, also called nodules formed in the filamentary structure of the current can be a source of the energy capable of accelerating the fast charged particles.

The influence of the nitrogen admixture on the evolution of a deuterium pinch column

  • DOI: 10.1063/1.4960825
  • Odkaz: https://doi.org/10.1063/1.4960825
  • Pracoviště: Katedra fyziky
  • Anotace:
    The application of a mixture of nitrogen and deuterium for the gas-puffing along the anode axis in deuterium plasma-focus discharges, as carried out at megaampere-level currents, enabled observations of the filamentary structure, and the decrease in the transformation velocity of the plasma column to be performed. It made possible to investigate the instability evolution during the production of hard X-rays and fast neutrons in more detail. The constriction of a plasma column transforms itself during the final phase of the compression into one or more small dense plasmoid-like structures which are separated by narrow necks. During the next phase, these structures start to decay by an expansion, in which a part of the plasma volume maintains its compactness. This evolution is explained by an increase and later decrease in the internal poloidal current component by reconnections of the associated magnetic lines, which are responsible for the acceleration of electron and ion beams.

Efficiency of ablative plasma energy transfer into a massive aluminum target using different atomic number ablators

  • DOI: 10.1017/S0263034615000452
  • Odkaz: https://doi.org/10.1017/S0263034615000452
  • Pracoviště: Katedra fyziky
  • Anotace:
    This paper aims at investigation of efficiency of an ablative plasma energy transfer into a massive aluminum target using different atomic number ablators. For this reason, several target materials representing a wide range of atomic numbers (Z = 3.5-73) were used. The experiment was carried out at the iodine Prague Asterix Laser System. The laser provided a 250 ps pulse with energy of 130 J at the third harmonic frequency (lambda(3) = 0.438 mu m). To study the plasma stream configurations a four-frame X-ray pinhole camera was used. The electron temperature of the plasma in the near-surface target region was measured by means of an X-ray spectroscopy. The efficiency of the plasma energy transport to the target was determined via the crater volume measurement using the crater replica technique. The experimental results were compared with two-dimensional numerical simulations where the plasma dynamics was based on the one-fluid, two temperature model, including radiation transport in diffusive approximation and ionization kinetics. It was shown that the plasma expansion geometry plays an important role in the ablative plasma energy transfer into the target.

Efficient generation of fast neutrons by magnetized deuterons in an optimized deuterium gas-puff z-pinch

  • DOI: 10.1088/0741-3335/57/4/044005
  • Odkaz: https://doi.org/10.1088/0741-3335/57/4/044005
  • Pracoviště: Katedra fyziky
  • Anotace:
    Z-pinch experiments with deuterium gas puffs have been carried out on the GIT-12 generator at 3 MA currents. Recently, a novel configuration of a deuterium gas-puff z-pinch was used to accelerate deuterons and to generate fast neutrons. In order to form a homogeneous, uniformly conducting layer at a large initial radius, an inner deuterium gas puff was surrounded by an outer hollow cylindrical plasma shell. The plasma shell consisting of hydrogen and carbon ions was formed at the diameter of 350 mm by 48 plasma guns. A linear mass of the plasma shell was about 5 ug/cm whereas a total linear mass of deuterium gas in single or double shell gas puffs was about 100 mu g/cm. The implosion lasted 700 ns and seemed to be stable up to a 5 mm radius. During stagnation, m = 0 instabilities became more pronounced. When a disruption of necks occurred, the plasma impedance reached 0.4 Omega and high energy (>2 MeV) bremsstrahlung radiation together with high energy deuterons were produced. Maximum neutron energies of 33 MeV were observed by axial time-of-flight detectors. The observed neutron spectra could be explained by a suprathermal distribution of deuterons with a high energy tail. Neutron yields reached 3.6x10(12) at a 2.7 MA current. A high neutron production efficiency of 6x10(7) neutrons per one joule of plasma energy resulted from the generation of high energy deuterons and from their magnetization inside plasmas.

Efficient neutron production from sub-nanosecond laser pulse accelerating deuterons on target front side

  • DOI: 10.1063/1.4931460
  • Odkaz: https://doi.org/10.1063/1.4931460
  • Pracoviště: Katedra fyziky
  • Anotace:
    Neutron-producing experiments have been carried out on the Prague Asterix Laser System. At the fundamental wavelength of 1.315 μm, the laser pulse of a 600 J energy and 300 ps duration was focused on a thick deuterated-polyethylene target. A more detailed analysis of neutron time-of-flight signals showed that a significant fraction of neutron yields was produced both by the 2H(d,n)3He reaction and by other neutron-producing reactions. Neutron energies together with delayed neutron and gamma emission showed that MeV deuterons escaped from a laser-produced plasma and interacted ≈50 ns later with a borosilicate blast-shield glass.

Electromagnetic pulses produced by expanding laser-produced Au plasma

  • DOI: 10.1515/nuka-2015-0043
  • Odkaz: https://doi.org/10.1515/nuka-2015-0043
  • Pracoviště: Katedra fyziky
  • Anotace:
    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 x 10(16) W/cm(2). 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.

Existence of a return direction for plasma escaping from a pinched column in a plasma focus discharge

  • DOI: 10.1063/1.4921248
  • Odkaz: https://doi.org/10.1063/1.4921248
  • Pracoviště: Katedra fyziky
  • Anotace:
    The use of multi-frame interferometry used on the PF-1000 device with the deuterium filling showed the existence of a return motion of the top of several lobules of the pinched column formed at the pinched plasma column. This phenomenon was observed in the presence of an over-optimal mass in front of the anode, which depressed the intensity of the implosion and the smooth surface of the pinched plasma column. The observed evolution was explored through the use of closed poloidal currents transmitted outside the pinched plasma. This interpretation complements the scenario of the closed currents flowing within the structures inside the pinched column, which has been published recently on the basis of observations from interferometry, neutron, and magnetic probe diagnostics on this device.

Investigation of compression of puffing neon by deuterium current and plasma sheath in plasma focus discharge

  • DOI: 10.1063/1.4922483
  • Odkaz: https://doi.org/10.1063/1.4922483
  • Pracoviště: Katedra fyziky
  • Anotace:
    This paper presents the results of the research of the influence of compressed neon, injected by the gas-puff nozzle in front of the anode axis by the deuterium current and plasma sheath on the evolution of the pinch, and neutron production at the current of 2 MA. The intense soft X-ray emission shows the presence of neon in the central region of the pinch. During the implosion and stopping of the plasma sheath, the deuterium plasma penetrates into the internal neon layer. The total neutron yield of 1010–1011 has a similar level as in the pure deuterium shots. The neutron and hard X-ray pulses from fusion D-D reaction are as well emitted both in the phase of the stopping implosion and during the evolution of instabilities at the transformation of plasmoidal structures and constrictions composed in this configuration from both gases. The fast deuterons can be accelerated at the decay of magnetic field of the current filaments in these structures.

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

  • DOI: 10.1515/nuka-2015-0064
  • Odkaz: https://doi.org/10.1515/nuka-2015-0064
  • Pracoviště: Katedra fyziky
  • Anotace:
    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.

Puffing Deuterium Compressed by a Neon Plasma Sheath at the Initial Poloidal Magnetic Field in Plasma Focus Discharge

  • DOI: 10.1109/TPS.2015.2431858
  • Odkaz: https://doi.org/10.1109/TPS.2015.2431858
  • Pracoviště: Katedra fyziky
  • Anotace:
    This paper presents the results of the experimental study of the influence of the applied poloidal magnetic field on the transformation of the plasma column formed by the compression of (10 ± 3)-μg/cm deuterium injected by the gas-puff nozzle in front of the anode axis by the neon plasma sheath of (50 ± 10) μg/cm at a current of 2 MA. The permanent magnet with an initial induction of 20–40 mT placed inside the anode: 1) increased the diameter of the pinch and of the stagnation; 2) depressed the evolution of instabilities and formation of the dense structures in the column; 3) delayed the dip of the current derivative in time (and start of the hard X-ray and neutron emission) 200–300 ns after the first peak of the soft X-ray emission (and the pinch with a minimal diameter near the anode); and 4) decreased the total neutron yield to 10–20%. These results were interpreted in terms of the increase in the repulsive pressure of the compressed poloidal magnetic field, which ncreases the stabilizing helicity of the discharge current. The transformations are independent of the polarity of the magnet.

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

  • DOI: 10.1515/nuka-2015-0065
  • Odkaz: https://doi.org/10.1515/nuka-2015-0065
  • Pracoviště: Katedra fyziky
  • Anotace:
    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.

The hydrodynamic and radiative properties of low-density foams heated by x-rays

  • Autoři: Rosmej, ON, Suslov, N., Martsovenko, D., Vergunova, G., Borisenko, N., Orlov, N., Rienecker, T., prof. Ing. Daniel Klír, Ph.D., Ing. Karel Řezáč, Ph.D., Orekhov, A., Borisenko, L., Krousky, E., Pfeifer, M., Dudzak, R., Maeder, R., Schaechinger, M., Schoenlein, A., Zaehter, S., Jacoby, J., Limpouch, J., Ullschmied, J., Zhidkov, N.
  • Publikace: Plasma Physics and Controlled Fusion. 2015, 57(094001), ISSN 0741-3335.
  • Rok: 2015
  • DOI: 10.1088/0741-3335/57/9/094001
  • Odkaz: https://doi.org/10.1088/0741-3335/57/9/094001
  • Pracoviště: Katedra fyziky
  • Anotace:
    n advanced type of hydrodynamic stable plasma targets with homogeneous distribution of plasma parameters has been proposed for application in experiments on heavy ion stopping in plasmas and relativistic laser based particle acceleration. Plasma was created via x-ray heating of polymer aerogels with a mean density 103 times lower than that of solid matter. Hydrodynamic and radiation properties of low-density polymer aerogels heated by x-rays, which were generated due to laser interaction with a gold hohlraum, have been investigated experimentally and numerically. In experiments carried out at the PALS laser facility in Prague, the parameters of the hohlraum based soft x-ray source and the fraction of x-ray energy absorbed by foam layers have been measured. The results of these experiments and numerical simulations show that the x-ray heat process occurs via propagation of supersonic radiation driven heat waves. The measured heat wave velocity of 107 cm s−1 allows one to estimate the plasma temperature reached as 25 eV. The hydrodynamic stability of x-ray heated plasma layers has been demonstrated by means of an optical streak camera viewing the plasma expansion process. Simulations of the foam heating process denote rather homogeneous distribution of the plasma temperature and density in the x-ray heated plasma layer and sharp plasma boundaries. The investigated features of such plasma targets are a great advantage for experiments with heavy ion and relativistic laser beams.

Current flow and energy balance during the evolution of instabilities in the plasma focus

  • DOI: 10.1088/0031-8949/2014/T161/014044
  • Odkaz: https://doi.org/10.1088/0031-8949/2014/T161/014044
  • Pracoviště: Katedra fyziky
  • Anotace:
    The unique diagnostic system at the plasma focus PF-1000 at the IPPLM in Warsaw, operating at 2MA and 1011 neutron yield, provides interferometry, x-ray, magnetic probes and neutron diagnostics together with registration of the voltage, current and its time derivative. With these diagnostic data we determined the boundaries of the dense plasma column from the interferograms and calculated the inductance for a single shot. The value of the current, voltage, current derivative, inductance and its derivative enabled calculation of the energy delivered to the pinch and energy released by the change of the inductance. The energy released during the expansion of the constriction was compared with the energy needed for acceleration of the deuterons producing neutrons calculated from the neutron pulse registered during and after the constriction expansion. The energy released by the expansion of the constriction is sufficient for deuteron acceleration.

Efficient Neutron Production from a Novel Configuration of Deuterium Gas-Puff Z-Pinch

  • DOI: 10.1103/PhysRevLett.112.095001
  • Odkaz: https://doi.org/10.1103/PhysRevLett.112.095001
  • Pracoviště: Katedra fyziky
  • Anotace:
    A novel configuration of a deuterium z pinch has been used to generate fusion neutrons. Injecting an outer hollow cylindrical plasma shell around an inner deuterium gas puff, neutron yields from DD reactions reached Y-n = (2.9 +/- 0.3) x 10(12) at 700 ns implosion time and 2.7 MA current. Such a neutron yield means a tenfold increase in comparison with previous deuterium gas puff experiments at the same current generator. The increase of beam-target yields was obtained by a larger amount of current assembled on the z-pinch axis, and subsequently by higher induced voltage and higher energies of deuterons. A stack of CR-39 track detectors on the z-pinch axis showed hydrogen ions up to 38 MeV. Maximum neutron energies of 15 and 22 MeV were observed by radial and axial time-of-flight detectors, respectively. The number of DD neutrons per one joule of stored plasma energy approached 5 x 10(7). This implies that deuterium gas puff z pinches belong to the most efficient plasma-based sources of DD neutrons.

Filamentary structure of plasma produced by compression of puffing deuterium by deuterium or neon plasma sheath on plasma-focus discharge

  • DOI: 10.1063/1.4903906
  • Odkaz: https://doi.org/10.1063/1.4903906
  • Pracoviště: Katedra fyziky
  • Anotace:
    The present experiments were performed on the PF-1000 plasma focus device at a current of 2 MA with the deuterium injected from the gas-puff placed in the axis of the anode face. The XUV frames showed, in contrast with the interferograms, the fine structure: filaments and spots up to 1mm diameter. In the deuterium filling, the short filaments are registered mainly in the region of the internal plasmoidal structures and their number correlates with the intensity of neutron production. The longer filamentary structure was recorded close to the anode after the constriction decay. The long curve-like filaments with spots were registered in the big bubble formed after the pinch phase in the head of the umbrella shape of the plasma sheath. Filaments can indicate the filamentary structure of the current in the pinch. Together with the filaments, small compact balls a few mm in diameter were registered by both interferometry and XUV frame pictures. They emerge out of the dense column and their life-time can be greater than hundreds of ns.

Generation of high-energy neutrons with the 300-ps-laser system PALS

  • DOI: 10.1017/hpl.2014.25
  • Odkaz: https://doi.org/10.1017/hpl.2014.25
  • Pracoviště: Katedra fyziky
  • Anotace:
    The laser system PALS, as a driver of a broad-beam ion source, delivered deuterons which generated neutrons with energies higher than 14 MeV through the Li-7(d, n)Be-8 reaction. Deuterons with sub-MeV energy were accelerated from the front surface of a massive CD2 target in the backward direction with respect to the laser beam vector. Simultaneously, neutrons were emitted from the primary CD2 target and a secondary LiF catcher. The total maximum measured neutron yield from D-2(d, n)(HeLi)-He-3-Li-7(d, n)Be-8,C-12(d, n)N-13 reactions was similar to 3.5(+/- 0.5) x 10(8) neutrons/shot.

Influence of an external magnetic field on the dynamics of a modified plasma focus

  • DOI: 10.1088/0031-8949/2014/T161/014042
  • Odkaz: https://doi.org/10.1088/0031-8949/2014/T161/014042
  • Pracoviště: Katedra fyziky
  • Anotace:
    The stability of a plasma column and the evolution of discharges are strongly dependent on the axial magnetic field. Internal axial and radial components of the magnetic field are formed at high current discharges naturally, but they can be also produced artificially by auxiliary coils or permanent magnets. The PFZ-200 facility was modified for the experiments with an external axial magnetic field. On this facility, an anti-electrode was placed along the z-axis in front of the anode. The auxiliary coils or permanent magnets generating the axial magnetic field were placed inside the anode and anti-electrode. Using micro-channel plate diagnostics, the stability of the plasma column at an axial magnetic field was studied. At the discharges in deuterium gas, the neutron production and the generation of hard x-rays were diagnosed with the scintillation detectors.

Measurement of the Target Current and EMP on Terawatt Laser System PALS

  • Pracoviště: Katedra fyziky
  • Anotace:
    The experiments are performed at high-power photodissociation iodine laser (1.315 μm, E=<1 kJ, t = 400 ps, I=6x10E16 W/cm2) at thePALSResearchCenterinPrague.During interaction of a focused intensive laser pulse with a solid target fast electrons are escaping and the target becomes charged. This charge can be neutralized by current flowing throw the target holder to the ground. The current with large time derivation, which is related to the laser pulse shape and to the inductance of the grounding circuit, generates a electromagnetic pulse in radio or microwave frequency band. Because the interaction chamber is usually equipped by a glass windows, insulators for galvanic separation, cables and so on, the electromagnetic pulse (EMP) passes out from the interaction chamber. At high-power laser facilities the EMP disturbs electrical signals, causes incorrect work of diagnostics, computers or control equipment. The study of target currents and EMP is important for design of all diagnostic instruments and projects of the large laser systems.

Measurement of the target current by inductive probe during laser interaction on terawatt laser system PALS

  • DOI: 10.1063/1.4898016
  • Odkaz: https://doi.org/10.1063/1.4898016
  • Pracoviště: Katedra fyziky
  • Anotace:
    Measurements of the return-current flowing through a solid target irradiated with the sub-nanosecond kJ-class Prague Asterix Laser System is reported. A new inductive target probe was developed which allows us measuring the target current derivative in a kA/ns range. The dependences of the target current on the laser pulse energy for cooper, graphite, and polyethylene targets are reported. The experiment shows that the target current is proportional to the deposited laser energy and is strongly affected by the shot-to-shot fluctuations. The corresponding maximum target charge exceeded a value of 10 μC. A return-current dependence of the electromagnetic pulse produced by the laser-target interaction is presented.

Neutron production from puffing deuterium in plasma focus device

  • DOI: 10.1063/1.4892551
  • Odkaz: https://doi.org/10.1063/1.4892551
  • Pracoviště: Katedra fyziky
  • Anotace:
    The current research has continued on the PF-1000 plasma focus device at the current of 2 MA by comparison of the shots with and without injected deuterium. The increase of the total neutron yield at the level of 1010–1011 per shot was achieved after the compression of about 10 lg/cm of the deuterium from the gas-valve by about 46 lg/cm of the neon or deuterium plasma sheath. It increases five times at the decrease of the puffing deuterium mass to one-half. In shots with neon in the chamber and with puffing deuterium, a considerable decrease was confirmed of the soft X-ray emission in comparison with shots without deuterium injection. This decrease can be explained by the absence of the neon in the region of the compressed and hot plasma. The deuterium plasma from the gas-puff should then be confined in the internal structures both in the phase of implosion as well as during their formation and transformation. In shots with puffing deuterium, the evolution of instabilities in the plasma column was suppressed. The deuterium plasma has a higher conductance and better ability to form expressive and dense plasmoids and to transport the internal current in comparison with neon plasma. Neutrons were produced both at the initial phase of stagnation, as well as at a later time at the evolution of the constrictions and dense plasmoids. VC 2014 AIP Publishing LLC.

Characterization of neutron emission from mega-ampere deuterium gas puff Z-pinch at microsecond implosion times

  • DOI: 10.1088/0741-3335/55/8/085012
  • Odkaz: https://doi.org/10.1088/0741-3335/55/8/085012
  • Pracoviště: Katedra fyziky
  • Anotace:
    Experiments with deuterium (D-2) triple shell gas puffs were carried out on the GIT-12 generator at a 3 MA current level and microsecond implosion times. The influence of the mass of deuterium shells on neutron emission times, neutron yields and neutron energy spectra was studied.

Correlation of X-ray emission with interferometry and neutron diagnostics at tungsten anode face and deuterium filling in plasma-focus discharge

  • DOI: 10.1088/0741-3335/55/11/115005
  • Odkaz: https://doi.org/10.1088/0741-3335/55/11/115005
  • Pracoviště: Katedra fyziky
  • Anotace:
    In this paper, the influence of the tungsten evaporated from the anode on neutron production and soft X-ray radiation was studied on the base of X-ray, interferometry and neutron diagnostics performed on the plasma focus PF-1000 device with deuterium as the filling gas at the current of 2 MA and neutron yield above 1010. In the axial center of the anode face the copper circuit plate was substituted with a tungsten one. During the pinch, the tungsten ions evaporated from the anode were transported into the plasma column. The differences in the filters used in the MCP X-frames and PIN detectors enabled separation of the bremsstrahlung emitted by the deuterium plasma from the recombination radiation of the tungsten ions produced in the region of the plasma column near the anode at the time of the evolution of instabilities. In comparison with the copper anode face, the neutron yield decreased to 40 % and the energy of deuterons producing neutrons to 80%.

ESTIMATION OF AMOUNT OF SCATTERED NEUTRONS AT DEVICES PFZ AND GIT-12 BY MCNP SIMULATIONS

  • Pracoviště: Katedra fyziky
  • Anotace:
    Our work is dedicated to pinch effect occurring during current discharge in deuterium plasma, and our results are connected with two devices – plasma focus PFZ, situated in the Faculty of Electrical Engineering, CTU, Prague, and Z-pinch GIT-12, which is situated in the Institute of High Current Electronics, Tomsk. During fusion reactions that proceed in plasma during discharge, neutrons are produced. We use neutrons as instrument for plasma diagnostics. Despite of the advantage that neutrons do not interact with electric and magnetic fields inside device, they are inevitably scattered by materials that are placed between their source and probe, and information about plasma from which they come from is distorted. For estimation of rate of neutron scattering we use MCNP code.

Generation of Secondary Particles from Subnanosecond Laser Irradiation of Targets at Intensities of 10(16) W cm(-2)

  • DOI: 10.1109/TPS.2013.2254134
  • Odkaz: https://doi.org/10.1109/TPS.2013.2254134
  • Pracoviště: Katedra fyziky
  • Anotace:
    Emission of several tens of mA/cm(2) currents carried by MeV-protons is reported for plasmas produced by a beam of the 3-TW kJ-class Prague Asterix Laser System (PALS) focused onto foil targets of various thicknesses. The maximum proton energy of 4.2 MeV is observed at a modest irradiance (I lambda(2) similar to 2 x 10(16) W cm(-2) mu m(2)). According to the maximum ion energy scaling E-M similar to (I lambda(2))(0.4) found for picosecond lasers such a value should be reached at I lambda(2) similar to 3 x 10(18) W cm(-2) mu m(2). Enhancement of the maximum proton energy can be explained by nonlinear interaction of the PALS laser beam with the generated plasma. Nonlinear effects also result in enhancement in the yield of fusion neutrons from CD2 plasma. The obtained yield of 4 x 10(5) DD-neutrons per laser energy is comparable to those obtained by the use of ps- and fs-lasers irradiating targets with I lambda(2) similar to 10(19) W cm(-2) mu m(2).

Influence of the external magnetic field on the pinch evolution and neutron production in plasma-focus discharge

  • DOI: 10.1088/0741-3335/55/11/115013
  • Odkaz: https://doi.org/10.1088/0741-3335/55/11/115013
  • Pracoviště: Katedra fyziky
  • Anotace:
    In this paper, the results of the study of the influence of the applied external axial magnetic field on the dynamics of the pinch and neutron production are presented, following from the measurements using X-ray, interferometry and neutron diagnostics performed on the plasma focus PF-1000 device with deuterium as the filling gas at the current of 2 MA and neutron yield above 1010. The permanent magnets with a magnetic field of a few hundredths of tesla were used both inside the anode body and in front of the end of the dense column. This magnetic field decreases the neutron yield, depresses the implosion velocity and the velocity of the transformations of internal structures, stabilizes the pinch column, increases its axial symmetry and indirectly confirms the existence of internal closed currents inside the pinch structures.

Observation of repetitive bursts in emission of fast ions and neutrons in sub-nanosecond laser-solid experiments

  • DOI: 10.1017/S0263034613000360
  • Odkaz: https://doi.org/10.1017/S0263034613000360
  • Pracoviště: Katedra fyziky
  • Anotace:
    A massive deuterated polyethylene target was exposed to laser intensities of about 3 x 10(16) W/cm(2) employing the 3-TW Prague Asterix Laser System (PALS). We achieved a yield of 2 x 10(8) neutrons per laser shot. Average time-of-flight signals of scintillation detectors operated in current mode reveal broad energy spectra of fusion neutrons with dominating energy of about 2.45 MeV. The energy dependence of the neutron yield shows a consistency in results of nanosecond, picosecond and sub-picosecond experiments. Here we also show that ions emitted in the backward direction from the front target surface have a multi-peak energy spectrum, which is caused by burst emission mechanisms.

Plastic plasma interaction with plasmas with growing atomic number

  • DOI: 10.2478/s11534-013-0218-0
  • Odkaz: https://doi.org/10.2478/s11534-013-0218-0
  • Pracoviště: Katedra fyziky
  • Anotace:
    This paper describes the investigation of the influence of target material atomic number (Z) on the laser-produced plasma pressure. For this reason, several target materials representing a wide range of atomic numbers (Z = 3.5 - 73), i.e. plastic (CH), Al, Cu, Ag, and Ta, were used. The results presented show that the plasma pressure decreases with growing atomic number but in a limited range of Z only. For higher Z, starting approximately from Z = 47 (Ag), the plasma pressure becomes constant, as confirmed by interferometric measurements and x-ray plasma imaging.

Scenario of Pinch Evolution in a Plasma Focus Discharge

  • DOI: 10.1088/0741-3335/55/3/035011
  • Odkaz: https://doi.org/10.1088/0741-3335/55/3/035011
  • Pracoviště: Katedra fyziky
  • Anotace:
    In this paper, the possible evolution of the pinched plasma column is presented following from the results of the temporally resolved measurements using magnetic probe, interferometry and neutron diagnostics performed on the plasma focus PF-1000 device with deuterium as the filling gas. Together with the discharge axial current about 1.5 MA a toroidal current component of the order of 100 kA was estimated in the toroidal, helical, and plasmoidal structures formed within the dense plasma column. The mass inside these structures increases due to injection of the plasma from the neighborhood regions with a higher pinching pressure. This injected plasma increases the intensity of the internal magnetic field, probably through turbulent motion and magnetic dynamo effect. The neutrons from the D-D fusion reaction, produced during the formation and decay of plasmoidal structures and constrictions, are accompanied by the changes of the axial component of the magnetic field. Then, the transformation and decay of internal closed currents can contribute to the acceleration of high-energy electrons and ions.

Search for Drive Parameter of Neutron-Optimized Z-Pinches and Dense Plasma Foci

  • DOI: 10.1109/TPS.2013.2283890
  • Odkaz: https://doi.org/10.1109/TPS.2013.2283890
  • Pracoviště: Katedra fyziky
  • Anotace:
    Dense plasma foci and deuterium gas puff Z-pinches are studied as sources of fusion neutrons. To design a neutron-optimized plasma focus, the drive parameter has been discussed in the last 15 years. This optimal value can be explained by a tradeoff between the energy of fast deuterons and the number of fast and target deuterons. Obtained experimental results show that the optimal drive parameter cannot be fully explained without the consideration of ion acceleration mechanisms to fusion energies.

The Construction Of The Fast Resistive Bolometer For a SXR Measurement On The GIT-12 Facility

  • Pracoviště: Katedra fyziky
  • Anotace:
    A lot of kinds of instruments are used for the SXR measurement at pulsed power facilities, but most of them are difficult to calibrate absolutely. For the determination of the energy of SXR radiated by the discharge on Z-pinches, it is possible to use the bolometer which can be calibrated analytically. The bolometer can be constructed with the sufficient sensitivity and, at the same time, with the time resolution in the order of nanoseconds. This bolometer was designed and constructed for the measurement on the 5MA facility GIT-12 at the Institute of High Current Electronics (IHCE) of the Siberian Branch Russian Academy of Sciences in Tomsk. The experiments on GIT-12 with the neon and deuterium gas-puff load were diagnosed by the copper bolometer with the time resolution of 4 ns and the sensitivity of 12Vcm2 J−1.

Characterization of the Neutron Production in the Modified MA Plasma-Focus

Correlation of Magnetic Probe and Neutron Signals with Interferometry Figures on the Plasma Focus Discharge

  • DOI: 10.1088/0741-3335/12/105023+10$33.00
  • Odkaz: https://doi.org/10.1088/0741-3335/12/105023+10$33.00
  • Pracoviště: Katedra fyziky
  • Anotace:
    In this paper the results of temporally resolved measurements using calibrated azimuthal and axial magnetic probes are presented, together with interferometry and neutron diagnostics performed on the PF-1000 (IPPLM, Warsaw, 2 MA) device with a deuterium filling and 1011 neutron yield. The probes located in the anode front at three different radial positions allow determination of the dominant part of the discharge current flows behind the imploding dense plasma layer. The current sheath is composed of both the axial and azimuthal components of the magnetic field. After reaching the minimum diameter, the current sheath continues in a radial motion to the axis and then penetrates into the dense plasma column. At the final phase of stagnation, the dominant current passes through the dense column. The probes located at the axis of the anode front registered an increase and decrease 1n the pulse of the axial component of magnetic field in correlation with the formation and decay of the dense plasmoidal structure. The estimated values of the axial component of the magnetic field in the centre of the plasmoids in the first neutron pulse and close before its decay and dominant neutron production can reach 2 and 10 T, it is (10 - 30)% of the value of the azimuthal magnetic field of the dense column boundary.

Deuterium gas puff Z-pinch at currents of 2 to 3 mega-ampere

  • DOI: 10.1063/1.3696859
  • Odkaz: https://doi.org/10.1063/1.3696859
  • Pracoviště: Katedra fyziky
  • Anotace:
    Deuterium gas-puff experiments have been carried out on the GIT-12 generator at the Institute of High Current Electronics in Tomsk.

Distribution of the current during implosion and at pinch phase

  • Pracoviště: Katedra fyziky
  • Anotace:
    The plasma focus PF-1000 in the IPPLM in Warsaw, operating with 2 MA with 1011 neutron yield, was investigated with interferometry, x-ray and neutron diagnostics and magnetic probes. Also current, its derivative and voltage signals were obtained. During processed shots 9011 and 9013, the setting with anti-anode was used, making practically a Z-pinch type device from the PF-1000. The distance of the anti-anode was 3 cm [1]. Using interferometry, 16 interferometric pictures with millimeter spatial resolution were obtained, representing the distribution of plasma density. Their time step is 10-20 ns during a 220 ns period. Laser Nd:YLF with pulse duration below 1ns and a set of mirrors was used, splitting the main ray into 16 mutually delayed beams. Interferograms were processed with abelization and with developed applications into densitograms. Using magnetic probes [2], the temporal derivative of azimuthal magnetic field is registered at the anode front in radial distances of 4 and 1,3 cm which allows determination of the current density. Knowing the total current and velocity of passing current sheath we can estimate the radial distribution of the current. Further we presume that the distribution of the current is constant along the plasma column, which allows us to calculate the inductance of the plasma column and its time-derivative more accurately. The inductance is then compared with the calculation assuming that total current is passing the boundary of the dense plasma region, sinking in the plasma. This comparison will possibly give us means to calculate inductance from the changes of the dense plasma boundaries alone.

Energy Transformation in Column of Plasma Focus Discharges with Megaampere Currents

Improvement of time-of-flight methods for reconstruction of neutron energy spectra from D(d,n)3He fusion reactions

  • DOI: 10.1088/0741-3335/54/10/105011
  • Odkaz: https://doi.org/10.1088/0741-3335/54/10/105011
  • Pracoviště: Katedra fyziky
  • Anotace:
    This paper deals with time-of-flight diagnostics of relatively short neutron pulses from tens to hundreds of nanoseconds. The aim is to determine the time evolution of energy spectra. The diagnostic setup consists of several neutron detectors placed in one direction at different distances. This approach is improved by placing additional detectors in the opposite direction. How the reconstruction method works with two opposite directions is explained in this paper. Improvement is limited to the deuterium fusion reaction D(d,n)3He. However, the principles described here could be applied in various fusion experiments. The advantage of our approach is not only better reconstruction but also the partial elimination of the influence of scattered neutrons. The described method was applied in the processing of data from fusion experiments in the PF-1000 facility and provided time evolution of the neutron energy spectra with energy resolution of 50 keV. In these plasma-focus experiments, results indicated a non-thermal production mechanism of the predominant part of the neutrons produced.

Interferometry of the plasma focus equipped with forehead cathode

  • Pracoviště: Katedra fyziky
  • Anotace:
    The PF-1000 plasma-focus facility in Warsaw, equipped with Mather-type coaxial electrodes working with a deuterium filling, was modified by the addition of a cathode disk in front of the anode front-plate at a distance of 3 cm. The plasma was diagnosed with temporal resolved interferometry and neutron diagnostics. The modified electrode configuration showed an increase of the current in the pinch phase and a decrease of the total neutron yield. The lower total neutron yield is caused by a lower energy of deuterons producing the observed neutrons and by a decrease of the velocity of transformations of the structures in the pinch column.

Neutron Production From a Small Modified Plasma Focus Device

  • DOI: 10.1109/TPS.2012.2221167
  • Odkaz: https://doi.org/10.1109/TPS.2012.2221167
  • Pracoviště: Katedra fyziky
  • Anotace:
    Abstract-In this paper, the results are presented of the study of the pinch evolution in the modified small plasma-focus device at the current peak of 200 kA and with a deuterium filling. The disk conducting the cathode was placed 1 cm in front of the inner electrode (anode). The neutron yield reached 106-108 per shot. The evolution of the plasma was imaged with four pinhole XUV frames and two schlieren pictures. The neutron signals were registered with three scintillation detectors. The figures and signals were enabled to describe the pinch phase at the moment of hard X-ray and neutron production with a 2-ns temporal uncertainty. The results were similar to the results obtained on the PF-1000 at the current of 2 MA. The first neutron pulse is produced at the stagnation, and the dominant neutron production correlates with the disintegration of the dense plasma column. Additionally, the energies of fast neutrons and deuterons producing neutrons have similar values and distributions as in PF-1000.

Plastic plasma as a compressor of aluminum plasma at the PALS experiment

  • DOI: 10.1017/S0263034611000528
  • Odkaz: https://doi.org/10.1017/S0263034611000528
  • Pracoviště: Katedra fyziky
  • Anotace:
    In our earlier papers, we demonstrated that plasma pressure decreases with the growing atomic number of the target material. That experimentally confirmed fact brought about a question whether it would be possible to collimate the Al plasma outflow by using plastic plasma as a compressor. To prove that idea we used in our next experiments a plastic target with an Al cylindrical insert of 400 mu m in diameter. The measurements were carried out at the Prague Asterix Laser System iodine laser facility.

Search for thermonuclear neutrons in a mega-ampere plasma focus

  • DOI: 10.1088/0741-3335/54/1/015001
  • Odkaz: https://doi.org/10.1088/0741-3335/54/1/015001
  • Pracoviště: Katedra fyziky
  • Anotace:
    Experimental results indicated a fraction of thermonuclear neutrons on the mega-ampere current level. Neutron TOF signals showed that the neutron production was a multiphase process and more than one mechanism occurred simultaneously. The occurrence of the thermonuclear mechanism was most evident during the plasma stagnation at low deuterium pressures. At low filling pressures, the narrow width of the neutron energy spectra demonstrated an ion temperature of about 1 keV. The possibility of thermonuclear neutrons was studied also after the stagnation, during the main neutron emission.

The SXR bolometer design for measurement on the power Z-pinches

  • Pracoviště: Katedra fyziky
  • Anotace:
    Design and construction of the high speed SXR pulse bolometer and experiments on the GIT-12 facility at Institute of High Current Electronics (IHCE SB RAN) in Tomsk.

Experimental evidence of thermonuclear neutrons in a modified plasma focus

  • DOI: 10.1063/1.3555447
  • Odkaz: https://doi.org/10.1063/1.3555447
  • Pracoviště: Katedra fyziky
  • Anotace:
    The PF-1000 plasma focus was modified by adding the cathode disk 3 cm in front of the anode. This modification facilitated the evaluation of neutron energy spectra. Two neutron pulses were distinguishable. As regards the first neutron pulse, it lasted 40 ns during the plasma stagnation and it demonstrated high isotropy of neutron emission. A peak neutron energy detected upstream was 2.46 MeV. The full width of neutron energy spectra of 90 enabled to calculate an ion temperature of 1.2 keV. These parameters and a neutron yield of 1e9 corresponded to theoretical predictions for thermonuclear neutrons.

Fusion neutron detector for time-of-flight measurements in z-pinch and plasma focus experiments

  • DOI: 10.1063/1.3559548
  • Odkaz: https://doi.org/10.1063/1.3559548
  • Pracoviště: Katedra fyziky
  • Anotace:
    We have developed and tested sensitive neutron detectors for neutron time-of-flight measurements in z-pinch and plasma focus experiments with neutron emission times in tens of nanoseconds and with neutron yields between 1e6 and 1e12 per one shot.

Interaction of a laser-produced copper plasma jet with ambient plastic plasma

  • DOI: 10.1088/0741-3335/53/9/095003
  • Odkaz: https://doi.org/10.1088/0741-3335/53/9/095003
  • Pracoviště: Katedra fyziky
  • Anotace:
    This work is aimed at the investigation of mutual interaction of plastic (CH) and copper axially symmetric plasmas, and the dependence on the ratio of their ablated masses.

Interaction of Cu and plastic plasmas as a method of forming laser produced Cu plasma streams with a narrow jet or pipe geometry

  • DOI: 10.1063/1.3579396
  • Odkaz: https://doi.org/10.1063/1.3579396
  • Pracoviště: Katedra fyziky
  • Anotace:
    The use of axially symmetrical target compositions consisting of materials with low and high atomic numbers makes it possible to create different plasma stream configurations (e.g., very narrow jet or pipe). In the paper certain their applications are suggested.

Interferometry of the Plasma Focus with Forehead Cathode

  • Pracoviště: Katedra fyziky
  • Anotace:
    Diagnostics of the fusion reaction with interferometry, x-ray and neutron techniques with temporal, spatial and energy resolution

Matlab applications for processing of interferograms and oscilograms from PF-1000 experiments

  • Pracoviště: Katedra fyziky
  • Anotace:
    This work presents development and usage of applications for processing and adjustments of data obtained during PF-1000 experiments in Warsaw

MCNP Calculations of the Spectrum of Scattered Neutrons at PFZ device

  • Pracoviště: Katedra fyziky
  • Anotace:
    Determination of the part of scaterd neutrons at the PFZ-device with calculation from signals of scintillation detectors using MCNP code

Mechanism of Production of Neutrons from D-D Reaction in PF and Z-pinch Discharges

  • Pracoviště: Katedra fyziky
  • Anotace:
    Results of neutron, hard X-ray, interferometry and magnetic probe diagnostics of the fusion DD reaction

Spontaneous Transformation in the Pinched Column of the Plasma Focus

The Noise Reduction of the Measured Signal in Plasma Diagnostics with Adaptive Filtration

  • Pracoviště: Katedra fyziky
  • Anotace:
    In the Wiener filtration the measured and reference signals are recorded in the channels of the osciloskops and the reference noise passes through the adaptive filter

Application of a Bonner sphere spectrometer for determination of the energy spectra of neutrons generated by 1 MJ plasma focus

  • Pracoviště: Katedra fyziky
  • Anotace:
    The spectra of neutrons outside the plasma focus device PF-1000 with an upper energy limit of 1 MJ was measured using a Bonner spheres spectrometer in which the active detector of thermal neutrons was replaced by nine thermoluminescent chips. As an a priori spectrum for the unfolding procedure, the spectrum calculated by means of the Monte Carlo method with a simplified model of the discharge chamber was selected. Differences between unfolded and calculated spectra are discussed with respect to properties of the discharge vessel and the laboratory layout.

Arrangement of the Experimental Setup for Determination of Average Kinetic Energy of Reacting Deuterons in Fusion Z-pinch Experiments

  • Pracoviště: Katedra fyziky
  • Anotace:
    The kinetic energy of reacting deuterons is one of the important parameter of the fusion plasma where deuterium is presented in a load. The energy of deuterons is determined from the reconstructed neutron energy spectra which are obtained by extended time-of-flight (TOF) method where time-resolved neutron detectors are placed at several distances on two opposite directions from the neutron source. Provided that the deuteron energy is much smaller than the fusion Q-value, it is possible to show that the neutron energy is only a function of the component of the deuteron kinetic energy (and vice versa) in the direction of neutron detection. Consequently, the side-on and end-on energy components of deuterons can be found on the basis of TOF measurement of neutrons in the radial and axial directions. Finally, the average kinetic energy of reacting deuterons can be evaluated on an assumption of radial symmetry of neutron production from Z-pinch plasma.

Developing of High-Speed Electromagnetic Deuterium Valve for Gas-Puff in Z-Pinch

  • Pracoviště: Katedra fyziky
  • Anotace:
    Studies of the mechanism of neutron production in the D(d,n)3He reactions are the main purpose of our experiments. The gas-puff is the most effective load for Z-pinch discharges for neutron generation. The Gas-puff valves for experiments on the S-300 facility in RRC Kurchatov Institute in Moscow have developed since year 2007. Maximum current peak in the S-300 facility is 4 MA. Development of the electromagnetically triggered gas-puff valve began in October 2008. The main experiments with this electromagnetic valve were done in the RRC Kurchatov Institute Moscow in September and October 2009. There were done 11 shots with peak current of 2 MA with 100 ns rise time. The Z-pinch discharges in the gas-puff seems to be the way for achieve high neutron yields.

Discharges in Deuterium Gas-Puff

  • Pracoviště: Katedra fyziky
  • Anotace:
    Optimalization of the parameters of the electromagnetic valve for injection of the gas between electrodes

Efficient production of 100 keV deuterons in deuterium gas puff Z-pinches at 2MA current

  • DOI: 10.1088/0741-3335/52/6/065013
  • Odkaz: https://doi.org/10.1088/0741-3335/52/6/065013
  • Pracoviště: Katedra fyziky
  • Anotace:
    Deuterium gas puff experiments were carried out on the S-300 Z-pinch at the Kurchatov Institute in Moscow. Gas puffs imploded onto the axis before a current peak at about 100 ns. Fusion neutrons were generated after the gas puff implosion during global expansion of a plasma column. On the basis of experimental observations, we concluded that a total energy of deuterons accelerated to fusion energies was above 1.5 kJ. It is more than 15% of the energy input into a plasma. Therefore gas puff Z-pinches seem to be not only powerful sources of x-ray radiation but also efficient sources of 100 keV deuterons.

Experimental evidence of multimaterial jet formation with lasers

  • DOI: 10.1063/1.3511774
  • Odkaz: https://doi.org/10.1063/1.3511774
  • Pracoviště: Katedra fyziky
  • Anotace:
    Laser-produced multimaterial jets have been investigated at the Prague Asterix Laser System laser [ K. Jungwirth et al., Phys. Plasmas 8, 2495 (2001) ]. The method of jet production is based on the laser-plasma ablation process and proved to be easy to set up and robust. The possibility of multimaterial laboratory jet production is demonstrated and complex hydrodynamic flows in the jet body are obtained. Two complementary diagnostics in the optical ray and x-ray ranges provide detailed information about jet characteristics. The latter are in agreement with estimates and two-dimensional radiation hydrodynamic simulation results. The experiment provides a proof of principle that a velocity field could be produced and controlled in the jet body. It opens a possibility of astrophysical jet structure modeling in laboratory.

Fusion Plasma Diagnostics in the PF 1000 Device

  • Pracoviště: Katedra fyziky
  • Anotace:
    Detailed description of the neutron and X-ray diagnostic at the current level of 2 megaampers

Mechanism of Production of Neutrons from D-D Reaction in PF and Z-Pinch Discharges

  • Pracoviště: Katedra fyziky
  • Anotace:
    Scenario of acceleration of fast deuterons and generation of fusion neutrons using scintillation and interferometric diagnostics

Processing of Interferometric Data for Animated Display

  • Pracoviště: Katedra fyziky
  • Anotace:
    Interpolation of equidensity pictures with delay of 1 ns and their connection into one film

Research of D-D Fusion Reaction at the CTU in Prague

  • Pracoviště: Katedra fyziky
  • Anotace:
    Neutron and X-ray diagnostics at small plasma focus using anti-anode electrode configuration for application at PF-1000 facility

Transformation of the Pinched Column at a Period of the Neutron Production

  • DOI: 10.1109/TPS.2009.2036623
  • Odkaz: https://doi.org/10.1109/TPS.2009.2036623
  • Pracoviště: Katedra fyziky
  • Anotace:
    Interferometric diagnostics of the hot plasma generated by plasma focus at the2 MA current at the instant of neutron production from deutery fusion reacion

Determination of Deuteron Energy Distribution From Neutron Diagnostics in a Plasma-Focus Device

  • DOI: 10.1109/TPS.2008.2005899
  • Odkaz: https://doi.org/10.1109/TPS.2008.2005899
  • Pracoviště: Katedra matematiky, Katedra fyziky
  • Anotace:
    Fast neutrons from deuteron-deuteron fusion reactions were used for a study of fast deuterons in the PF-1000 plasma-focus device. The energy spectrum of neutrons was determined by the time-of-flight method using ten scintillation detectors positioned downstream, upstream, and side-on the experimental facility. Neutron energy-distribution functions enabled the determination of axial and radial components of energy of deuterons producing the fusion neutrons, as well as a rough evaluation of the total energy distribution of all fast deuterons in the pinch. It was found that the total deuteron energy-distribution function decreases with the deuteron energy more slowly than the tail of the Maxwellian distribution for 1-2-keV deuterons.

Deuteron Acceleration and Fusion Neutron Production in Z-pinch plasmas

  • Pracoviště: Katedra fyziky
  • Anotace:
    Fusion neutron measurements were carried out on the S-300 generator (Kurchatov Institute, Moscow). We tried deuterated fibers, various types of wire arrays imploding onto a deuterated fiber, and deuterium gas puffs as Z-pinch loads. On the current level of 2 MA, the peak neutron yield of 1010 was achieved with a deuterium gas-puff. The neutron and deuteron energy spectra were quite similar in various types of Z-pinch configurations. The broad width of radial neutron spectra implied a high radial component of deuteron velocity. On the basis of neutron measurements, we concluded that neutron production mechanism is connected with the study of plasma voltage. It means that the acceleration of fast deuterons is not a secondary process but it reflects the global dynamics of Z-pinch plasmas. For this reason it is useful to add deuterium as a "tracer" in Z-pinch loads more often. For instance, it seems attractive to prepare wire-arrays from deuterated metal wires such as Pd.

Interferometric Study of Pinch Phase in Plasma-Focus Discharge at the Time of Neutron Production

Neutron Energy Distribution Function Reconstructed From Time-of-Flight Signals in Deuterium Gas-Puff Z-Pinch

  • DOI: 10.1109/TPS.2008.2010860
  • Odkaz: https://doi.org/10.1109/TPS.2008.2010860
  • Pracoviště: Katedra fyziky
  • Anotace:
    The implosion of a solid deuterium gas-puff Z-pinch was studied on the S-300 pulsed power generator. The peak neutron yield above 1E10 was achieved on the current level of 2 MA. The fusion neutrons were generated at about 150 ns after the current onset, i.e., during the stagnation and at the beginning of the expansion of a plasma column. The neutron emission lasted on average 25 ns. The neutron energy distribution function was reconstructed from 12 neutron TOF signals by the Monte Carlo simulation. The side-on neutron energy spectra peaked at 2.42 +/- 0.04 MeV with about 450-keV FWHM. In the downstream direction (i.e., the direction of the current flow from the anode toward the cathode), the peak neutron energy and the width of a neutron spectrum were 2.6 +/- 0.1 MeV and 400 keV, respectively. The average kinetic energy of fast deuterons, which produced fusion neutrons, was about 100 keV. The generalized beam-target model probably fits best to the obtained experimental data.

Neutron Production and Fast Deuteron Characteristics at the Plasma Focus Discharge

  • Pracoviště: Katedra fyziky
  • Anotace:
    This paper summarized the results of interferometry, X-ray and neutron diagnostics performed at the plasma focus facility filled with deuterium. The fusion processes are produced mainly in the dense and hot spherical structure of 2 cm diameter 5 - 8 cm in front of the anode. The electron temperature of this structure is about 750 eV and the density 5x10^24 - 5x10^25. The neutron energy distribution was calculated using time of flight analysis and showed the dominant direction of the fast deuteron velocity downstream. The deuteron energy distribution was estimated supposing isotropy distribution of the sum of opposite orientation. The total number of fast deuterons in the energy range of 10-400 keV is about 10^18 with total energy of 20 kJ. Plasma in the spherical structure is heated dominantly with ion-ion Coulomb collisions of fast deuterons in the energy range below 10 keV.

Neutron Production at the Small Plasma-Focus Device With Antianode

Reconstruction of Time-Resolved Neutron Energy Spectra in Z-Pinch Experiments Using time-of-flight Method

  • Pracoviště: Katedra fyziky
  • Anotace:
    We present the reconstruction of neutron energy spectra from time-of-flight signals. This technique is useful in experiments with the time of neutron production in the range of about tens or hundreds of nanoseconds. The neutron signals were obtained by a common hard X-ray and neutron fast plastic scintillation detectors. The reconstruction is based on the Monte Carlo method which has been improved by simultaneous usage of neutron detectors placed on two opposite sides from the neutron source. Although the reconstruction from detectors placed on two opposite sides is more difficult and a little bit inaccurate (it followed from several presumptions during the inclusion of both sides of detection), there are some advantages. The most important advantage is smaller influence of scattered neutrons on the reconstruction. Finally, we describe the estimation of the error of this reconstruction.

Research of the Small Plasma Focus with an Auxiliary Electrode at Deuterium Filling

Study of D-D Fusion Reaction at Z-pinch Devices in 2009

  • Autoři: prof. RNDr. Pavel Kubeš, CSc., Kravárik, J., prof. Ing. Daniel Klír, Ph.D., Ing. Karel Řezáč, Ph.D., Paduch, M., Pisarzcyk, T., Scholz, M., Ivanova-Stanik, I., Chodukowski, T., Karpinski, L., Sadowski, M.J, Tomaszewski, K., Zielinska, E., Bakshaev, Yu, Chernenko, A., Kazakov, E., Korolev, V., Ananev, S., Zelenin, A., Ustroev, G.
  • Publikace: Proceedings of the Workshop and Expert Meeting ICDMP. Warsaw: IPPLM, 2009. pp. 1-44.
  • Rok: 2009
  • Pracoviště: Katedra fyziky
  • Anotace:
    Results of interferometry and x-ray diagnostics are used for description of the plasma transformation during neutron production

Anisotropy of the emission of DD-fusion neutrons caused by the plasma-focus vessel

  • Pracoviště: Katedra fyziky
  • Anotace:
    The anisotropic emission of DD-fusion neutrons emitted by the plasma focus device PF-1000 at the Institute of Plasma Physics and Laser Microfusion, Warsaw, was observed with the use of thermoluminescent dosimeters and fast-neutron moderators. The observed anisotropy is compared with the computational prediction of the anisotropy caused by the PF-1000 vessel, which scatters the expanding DD-neutrons. The resulting changes in the group energy spectrum of neutrons induced by their scattering on the discharge vessel are presented and their effect on time-of-flight spectra of neutrons is discussed.

Another Enlargment of the Program Neutrons for Reconstruction of the Neutron Energy Spectra in D-D Z-pinch Experiments

  • Pracoviště: Katedra fyziky
  • Anotace:
    Program Neutrons for Reconstruction of the Neutron Energy Spectra in D-D Z-pinch Experiments on the base of Monte-Carlo simulations

Dense Z-Pinches 2008

  • Pracoviště: Katedra fyziky
  • Anotace:
    Presentation of results from conference showes new experimental, simulation, theoretical and diagnostic knowledge

Deuterium Gas-Puff Z-Pinch at the Kurchatov Institute

  • Pracoviště: Katedra fyziky
  • Anotace:
    Results of neutron diagnostics from S-300 Z-Pinch at the Kurchatov Institute

Fusion D-D reaction at the PF-1000 in Frame of ICDMP

  • Pracoviště: Katedra fyziky
  • Anotace:
    Fusion D-D reaction at the PF-1000 in Frame of ICDMP was studied with x-ray, neutron and interferometric diagnostics

Mechanism of Production of Neutrons from D-D Reaction in Z-pinch Discharges

  • Pracoviště: Katedra fyziky
  • Anotace:
    Results of x-ray, neutron and interferometry diagnostics of D-D fusion reactions are base for determination of mechanism of fast ion acceleration

Neutron emission during the implosion of a wire array onto a deuterated fiber

  • Pracoviště: Katedra fyziky
  • Anotace:
    X-ray and neutron diagnostics of the radiation during the implosion of a wire array onto a deuterated fiber

Neutron emission generated during wire array Z-pinch implosion onto deuterated fiber

  • Pracoviště: Katedra fyziky
  • Anotace:
    Neutron and soft X-ray diagnostics of the emission generated during wire array Z-pinch implosion onto deuterated fiber

Research on the PF-1000 in 2008

  • Pracoviště: Katedra fyziky
  • Anotace:
    In the report the results of x-ray, neutron and interferometry diagnostics important for understanding of mechanism of acceleration of fast energy ions were presented

Time Resolved Neutron Energy Spectra Reconstruction from One Chain of TOF Detectors: Possibilities and Limitations

  • Pracoviště: Katedra fyziky
  • Anotace:
    Temporal resolution of energy spectra of fusion neutrons were calculated on the base of time-of-flight method and Monte Carlo simulations

Wire-Array Z-Pinch Implosion onto Deuterated Fibre at S-300 Generator

  • Pracoviště: Katedra fyziky
  • Anotace:
    Wire-Array Z-Pinch Implosion onto Deuterated Fibre at S-300 Generator enabled generation of fusion neutrons from D-D fusion reaction

D-D fusion neutrons generated in 500 J fibre Z-pinch

  • Pracoviště: Katedra fyziky
  • Anotace:
    Z-pinch, D-D fusion reaction, neutrons, plasma diagnostics

D-D reaction and fast deuterons in plasma focus facility

  • Autoři: prof. RNDr. Pavel Kubeš, CSc., prof. Ing. Daniel Klír, Ph.D., Kravárik, J., Ing. Karel Řezáč, Ph.D., Bienkowska, B., Ivanova-Stanik, I., Karpinski, L., Paduch, M., Scholz, M., Schmidt, H., Sadowski, M., Tomaszewski, K.
  • Publikace: Proceedings of XXVIII International Conference on Phenomena in Ionized Gases. Prague: Institute of Plasma Physics AS CR, v.v.i., 2007. pp. 1473-1475. ISBN 978-80-87026-01-4.
  • Rok: 2007
  • Pracoviště: Katedra fyziky
  • Anotace:
    Study of D-D reaction and fast deuterons in plasma focus facility

Fast Deuterons and Neutrons in Plasma Focus Discharge

  • Autoři: prof. RNDr. Pavel Kubeš, CSc., prof. Ing. Daniel Klír, Ph.D., Kravárik, J., Ing. Karel Řezáč, Ph.D., Litseva, E., Bienkowska, B., Tomaszewski, K., Karpinski, L., Ivanova-Stanik, I., Paduch, M., Scholz, M., Schmidt, H., Sadowski, M.J.
  • Publikace: 34thEPS Conference on Plasma Physics, 2 - 6 July 2007 Europhysics Conference Abstracts Vol. 31I (2007). Frankfurt: European Physical Society, 2007. pp. 1-4. ISBN 978-83-926290-0-9.
  • Rok: 2007

Fusion Neutrons Produced in Wire-Array Z-Pinch at S-300 Facility

  • Autoři: prof. Ing. Daniel Klír, Ph.D., Kravárik, J., prof. RNDr. Pavel Kubeš, CSc., Ing. Karel Řezáč, Ph.D., Ananev, S.S., Bakshaev, Yu.L., Blinov, P.I., Chernenko, A.S., Kazakov, E.D., Korolev, V.D., Meshcherov, B.R., Ustroev, G.I.
  • Publikace: 34thEPS Conference on Plasma Physics, 2 - 6 July 2007 Europhysics Conference Abstracts Vol. 31I (2007). Frankfurt: European Physical Society, 2007. pp. 1-4. ISBN 978-83-926290-0-9.
  • Rok: 2007

Generation of Neutrons from D-D Fusion Reactions at CTU

  • Pracoviště: Katedra fyziky
  • Anotace:
    Generation of Neutrons from D-D Fusion Reactions at CTU

Perspektivy energetických zdrojů

  • Pracoviště: Katedra fyziky
  • Anotace:
    Perspektivy energetických zdrojů

Reconstruction of D-D Neutron Energy Spectra from Time-Resolved Neutron Detectors Placed in Opposite Directions

  • Pracoviště: Katedra fyziky
  • Anotace:
    plasma diagnostics, D-D fusion neutrons, Monte Carlo reconstruction

Study of Axial Anisotropy of Neutron Yield in the Reconstruction of Neutron Energy Spectra in D-D Reaction

Study of Fusion Neutrons at PF-1000 in Frame ICDMP

  • Pracoviště: Katedra fyziky
  • Anotace:
    Study of Fusion Neutrons at PF-1000 in Frame ICDMP

Time Resolving Study of D-D Reaction at the Plasma Focus Device

  • Pracoviště: Katedra fyziky
  • Anotace:
    TIME RESOLVING STUDY OF D-D REACTION AT THE PLASMA FOCUS DEVICE

Time-resolved Energy Neutron Spectra in D-D Fusion Reactions

  • Pracoviště: Katedra fyziky
  • Anotace:
    Time-resolved Energy Neutron Spectra in D-D Fusion Reactions

Correlation of Radiation with Electron and Neutron Signals Taken in a Plasma-Focus Device

  • Pracoviště: Katedra fyziky
  • Anotace:
    Correlation of Radiation with Electron and Neutron Signals Taken in a Plasma-Focus Device

Generation of D-D Fusion Neutrons

Improvement of Methods Used for Reconstruction of Time Resolved Neutron Energy Spectra in D-D Fusion Reactions

Measurements of D-D neutrons in Z-Pinches

Monte Carlo Simulations for Reconstruction of Neutron Time-Resolving Energy Distribution in D-D Fusion Reactions

Monte Carlo Simulations for Time-Resolving Energy Distribution

  • Autoři: Ing. Karel Řezáč, Ph.D.,
  • Publikace: Proceedings of Workshop 2006. Praha: České vysoké učení technické v Praze, 2006. pp. 60-61. ISBN 80-01-03439-9.
  • Rok: 2006

Neutron Emission of Z-Pinch Discharges

  • Pracoviště: Katedra fyziky
  • Anotace:
    Neutron Emission of Z-Pinch Discharges

Neutron Energy Spectra at PF-1000

  • Pracoviště: Katedra fyziky
  • Anotace:
    Neutron Energy Spectra at PF-1000

Study DD- Neutrons in the Experiments on S-300 Pulsed Power Machine

  • Pracoviště: Katedra fyziky
  • Anotace:
    Study DD- Neutrons in the Experiments on S-300 Pulsed Power Machine

Time Delay of the Hard X-Ray and Neutron Emission at PF Facility

  • Pracoviště: Katedra fyziky
  • Anotace:
    Diagnostics of high energy particles

Motion of charged particles in common electric and magnetic fields

  • Autoři: Ing. Karel Řezáč, Ph.D.,
  • Publikace: Fifth International Workshop and Summer School " Towards Fusion Energy-Plasma Physics, Diagnotics, Applications. Warsaw: IPPLM, 2005. pp. 20-21.
  • Rok: 2005

Astronomie a fyzika na přelomu tisíciletí

Dobývání Marsu na přelomu let 2003 a 2004

Sluneční vítr

Interactive Physics via Java Applets

Java Applets Simulating Motion in Electric and Magnetic Fields

  • Autoři: Ing. Karel Řezáč, Ph.D.,
  • Publikace: Poster 2003. Praha: České vysoké učení technické v Praze, Fakulta elektrotechnická, 2003. p. 26. ISSN 0277-786X. ISBN 0-8194-5368-4.
  • Rok: 2003

Za stránku zodpovídá: Ing. Mgr. Radovan Suk