Jakub Cikhardt - Academia.edu (original) (raw)

Papers by Jakub Cikhardt

Research paper thumbnail of High Energy Density Plasma Diagnostics Using Neutron and Gamma Detectors

Deuterium Z-pinches are efficient sources of pulsed soft and hard x-rays, fast ions, and neutrons... more Deuterium Z-pinches are efficient sources of pulsed soft and hard x-rays, fast ions, and neutrons. Many phenomena related to an acceleration of ions and neutron production on the Z-pinches have not yet been explained. Detailed understanding of these phenomena could be multidisciplinary important. Therefore, these phenomena are investigated in joint Czech-Russian experiments on the terawatt class GIT-12 device with the generator output voltage of 600 kV and current at stagnation of about 3 MA. These experiments are interesting since by using the novel experimental load composed of the deuterium gas-puff with outer plasma shell, the neutron yields were significantly increased from the order of 10 to the order of 10. Such relatively high neutron yields were earlier observed on the devices with significantly higher current as the Saturn generator with the pulsed current of about 10 MA. At the same time, in our experiments, hydrogen ions with an energy above 38 MeV were detected. Such re...

Research paper thumbnail of Ion emission from plasmas produced by femtosecond pulses of short-wavelength free-electron laser radiation focused on massive targets: an overview and comparison with long-wavelength laser ablation

Optics Damage and Materials Processing by EUV/X-ray Radiation (XDam8)

Research paper thumbnail of Strongly magnetized plasma produced by interaction of nanosecond kJ-class laser with snail targets

Plasma Physics and Controlled Fusion

Magnetized plasma studies are necessary for many applied studies, including laser-driven inertial... more Magnetized plasma studies are necessary for many applied studies, including laser-driven inertial fusion, modeling astrophysically relevant phenomena, and innovative industrial and medical applications. An interesting method of generating highly magnetized plasma can be based on the interaction of a laser with spiral-shaped cavity (snail-like) targets. A target shaped in this way can represent the central area of a spherical pellet that is not irradiated radially, but rather through an entrance hole allowing the laser beam to almost impact its inner surface tangentially (Pisarczyk et al 2018 Sci. Rep. 8 17 895). In the reported experiment, snail targets of various diameters were irradiated by linearly or circularly polarized radiation of a Prague asterix laser system (PALS) iodine laser delivering ∼500 J, 350 ps and 1.315 μm pulses on targets. Three-frame complex interferometry demonstrated that plasma is generated on the entire inside and outside surfaces of the snail target, start...

Research paper thumbnail of Influence of the magnetic field on properties of hot electron emission from ablative plasma produced at laser irradiation of a disc-coil target

Plasma Physics and Controlled Fusion

Optical generators of strong magnetic fields based on the laser-driven-coil target (LDCT) concept... more Optical generators of strong magnetic fields based on the laser-driven-coil target (LDCT) concept are considered to be useful tools for studies of magnetized plasmas, in particular for the study of implosion of magnetized fusion targets in inertial fusion research and astrophysical applications. This paper presents results of the research directed at investigation of the plasma properties in a laser-induced magnetic field. In the experiment carried out on the kilojoule PALS laser facility, a generator of the magnetic field was a disc-coil (DC) target composed of a Cu disk coupled to a single-turn coil irradiated by a 1ω laser beam with an energy of 500 J. The attention was focused on examining the influence of the magnetic field on properties of the hot electron (HE) flux emitted from the front surface of the irradiated target. The 3-frame complex interferometry and 4-frame X-ray camera combined with the measurements of the HE population and energy using a multi-channel magnetic ele...

Research paper thumbnail of Improvement of Diagnostics for Measurement of Multi-MeV Ions Produced in Deuterium Gas-Puff Z-Pinch

APS Division of Plasma Physics Meeting Abstracts, 2019

Research paper thumbnail of Measurements of Early-Time Plasma Evolution in the Hawk Dense Plasma Focus

2018 IEEE International Conference on Plasma Science (ICOPS), 2018

The 650 kA Hawk pulsed power generator at NRL has been configured as a fast (1.2 μs), high in duc... more The 650 kA Hawk pulsed power generator at NRL has been configured as a fast (1.2 μs), high in ductance (607 nH) driver for a dense plasma focus load. The current pulse is initiated in a radially injected deuterium plasma. This plasma is accelerated through a coaxial region, and pinches onto neutral deuterium injected axially by a gas-puff valve. A ribbon beam interferometer is used to diagnose the plasma in the coaxial region at several radii, providing time resolved electron density measurements through the initiation and axial run-down phases of the implosion. We present interferometry results alongside imaging, spectroscopic, electrical, and radiation measurements that track the evolution of the imploding current sheath.

Research paper thumbnail of Organized Structeres, Magnetic Reconnections and Acceleration of Fast Beams in Plasma-Focus Fusion Plasma

2018 IEEE International Conference on Plasma Science (ICOPS), 2018

Fusion plasmas produced in tokamaks, inertial-fusion experiments with powerful lasers, and z-pinc... more Fusion plasmas produced in tokamaks, inertial-fusion experiments with powerful lasers, and z-pinch discharges, deal with similar questions concerning the generation of high energy beams of charge particles, similar to those emitted from plasmas in Universe1-3. In all cases, a fast release of magnetic energy during magnetic reconnections of various organized structures is often considered. Dense plasmas, which are produced in plasma-focus discharges, have some advantages in solving this problem, since they have very convenient parameters for complementary diagnostics with relative simple temporal-, spatial- and spectral-resolution. The described experimental research on DD fusion reactions was performed at the current intensity of about 1 MA and the total neutron yield of about 1010 per shot. A multi-frame interferometry system, scintillation detectors, as well as X -ray and corpuscular diagnostic equipment - made it possible to study the evolution of toroidal- and plasmoidal-structures, which were formed by closed currents with poloidal and toroidal components in filamentary forms. The production of hard X -rays and fusion neutrons correlated with the formation and decay of plasmoids4. The gained knowledge about evolution of the ordered structures, transformations of currents and magnetic fields - can be an inspiration for researchers of the tokamak- and laser-fusion as well as for astrophysicists community.

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

New Journal of Physics, 2020

Acceleration of ions to multi-MeV energies is investigated in various plasma devices to better un... more 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 × 1013 and 1011, respectively. Accelerated deuterons produced one 20 ns (full width at hal...

Research paper thumbnail of Neutron fluence distribution in experiments with 3 MA deuterium gas-puff z-pinch

Physics of Plasmas, 2020

Deuterium gas-puff z-pinches are very efficient laboratory sources of neutron pulses. Using a nov... more 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 5.6×1012 is reached. At the same time, a very broad neutron energy spectrum up to energies on the order of tens of MeV is observed. In these experiments, the neutrons are produced not only by the D(d,n)3He (DD) nuclear reaction but also by reactions of multi-MeV deuterons with the experimental hardware. The angular distribution of the neutron fluence and dependence of the fluence on the distance from the z-pinch are measured using neutron activation diagnostics. By this method, a number of produced non-DD neutrons and anisotropy of DD neutron emission are evaluated.

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

Plasma Physics and Controlled Fusion, 2020

Research paper thumbnail of Target current: a useful parameter for characterizing laser ablation

Laser and Particle Beams, 2017

A current flowing between the ground and target exposed to the nanosecond laser radiation is anal... more 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.

Research paper thumbnail of Electromagnetic pulse (EMP) radiation by laser interaction with a solid H2 ribbon

Physics of Plasmas, 2017

The electromagnetic pulses (EMPs) generated during the interaction of a focused 1.315-μm sub-nano... more The electromagnetic pulses (EMPs) generated during the interaction of a focused 1.315-μm sub-nanosecond laser pulse with a solid hydrogen ribbon were measured. The strength and temporal characteristics of EMPs were found to be dependent on the target density. If a low density target is ionized during the interaction with the laser, and the plasma does not physically touch the target holder, the EMP is weaker in strength and shorter in time duration. It is shown that during the H2 target experiment, the EMP does not strongly affect the response of fast electronic devices. The measurements of the EMP were carried out by Rohde&Schwarz B-Probes, particularly sensitive in the frequency range from 30 MHz and 1 GHz. Numerical simulations of resonant frequencies of the target chamber used in the experiment at the Prague Asterix Laser System kJ-class laser facility elucidate the peaked structure of EMP frequency spectra in the GHz domain.

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

Physics of Plasmas, 2017

The paper concerns important differences in the evolution of plasma column structures during the ... more 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.

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

Plasma Physics and Controlled Fusion, 2017

The current balancing the target charging and the emission of transient electromagnetic pulses (E... more The current balancing the target charging and the emission of transient electromagnetic pulses (EMP) driven by the interaction of a focused 1.315 μm 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.

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

Journal of Instrumentation, 2016

Recent experiments at the laser facility PALS focused on the laser driven fusion of deuterons are... more 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 3× 1016 W cm−2. In the reported experiments fast fusion neutrons with energy up to 16 MeV were produced through 7Li(d, n)8Be and 11B(d, n)12C 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 2H(d, n)3He reaction increased by a factor of about 5, from 4× 108 to 2× 109. 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.

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

Physics of Plasmas, 2015

This paper presents the results of the research of the influence of compressed neon, injected by ... more 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.

Research paper thumbnail of Acceleration of Hydrogen Ions up to 30 MeV and Generation of 3x10 12 Neutrons in Megaampere Deuterium Gas-Puff Z-Pinch

The peak neutron yield from DD reactions reached Y n = (2.9 ± 0.3) × 10 12 at 100 µg/cm linear ma... more The peak neutron yield from DD reactions reached Y n = (2.9 ± 0.3) × 10 12 at 100 µg/cm linear mass density of deuterium, 700 ns implosion time and 2.7 MA current. Such a neutron yield means that the scaling law of deuterium z-pinches Y n ∝ I 4 was extended to 3 MA currents. The further increase of neutron yields up to (3.7 ± 0.4) × 10 12 was achieved by placing a deuterated polyethylene catcher onto the axis. Maximum neutron energies of 15 and 22 MeV were observed by radial and axial nToF detectors, respectively. A stack of CR-39 track detectors showed up to 40 MeV deuterons (or 30 MeV protons) on the z-pinch axis. Since the energy input into plasmas was 70 kJ, the number of DD neutrons per one joule of stored plasma energy exceeded the value of 5 × 10 7. This value implies that deuterium gas-puff z-pinches belong to the most efficient plasma-based sources of DD neutrons.

Research paper thumbnail of Long-Implosion-Time Z-pinch Experiments with Deuterium Gas-Puffs on the GIT-12 Generator

Experiments with deuterium triple shell gas-puffs have been carried out on the GIT-12 generator a... more Experiments with deuterium triple shell gas-puffs have been carried out on the GIT-12 generator at the IHCE in Tomsk. Outer, middle, and inner nozzle diameters were 160 mm, 80 mm and 30 mm, respectively. The influence of the mass of deuterium shells on neutron emission times, neutron yields and neutron spectra was studied. The linear mass density of deuterium varied between 50 and 270 μg/cm. Gas puffs imploded onto the axis before the peak of a generator current at 700-1100 ns. The first neutron peak occurred during the stagnation. Most of the neutrons were emitted during the second neutron pulse after the development of instabilities. In lower mass gas puffs, neutron energies of up to 4.4 MeV gave the evidence of 1 MeV deuterons. The peak neutron yield from D(d,n)^3He reactions reached 3x10^11 on a current level of 2.5 MA. Secondary DT neutrons were measured by BDS-10000 bubble detectors. An average neutron yield ratio Y>10 MeV/Y2.5 MeV exceeded (6±3)x10-4. Ne-Ne-D2 and Ne-D2-D2...

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

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

Review of Scientific Instruments, 2014

Measurements of the return-current flowing through a solid target irradiated with the sub-nanosec... more 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.

Research paper thumbnail of High Energy Density Plasma Diagnostics Using Neutron and Gamma Detectors

Deuterium Z-pinches are efficient sources of pulsed soft and hard x-rays, fast ions, and neutrons... more Deuterium Z-pinches are efficient sources of pulsed soft and hard x-rays, fast ions, and neutrons. Many phenomena related to an acceleration of ions and neutron production on the Z-pinches have not yet been explained. Detailed understanding of these phenomena could be multidisciplinary important. Therefore, these phenomena are investigated in joint Czech-Russian experiments on the terawatt class GIT-12 device with the generator output voltage of 600 kV and current at stagnation of about 3 MA. These experiments are interesting since by using the novel experimental load composed of the deuterium gas-puff with outer plasma shell, the neutron yields were significantly increased from the order of 10 to the order of 10. Such relatively high neutron yields were earlier observed on the devices with significantly higher current as the Saturn generator with the pulsed current of about 10 MA. At the same time, in our experiments, hydrogen ions with an energy above 38 MeV were detected. Such re...

Research paper thumbnail of Ion emission from plasmas produced by femtosecond pulses of short-wavelength free-electron laser radiation focused on massive targets: an overview and comparison with long-wavelength laser ablation

Optics Damage and Materials Processing by EUV/X-ray Radiation (XDam8)

Research paper thumbnail of Strongly magnetized plasma produced by interaction of nanosecond kJ-class laser with snail targets

Plasma Physics and Controlled Fusion

Magnetized plasma studies are necessary for many applied studies, including laser-driven inertial... more Magnetized plasma studies are necessary for many applied studies, including laser-driven inertial fusion, modeling astrophysically relevant phenomena, and innovative industrial and medical applications. An interesting method of generating highly magnetized plasma can be based on the interaction of a laser with spiral-shaped cavity (snail-like) targets. A target shaped in this way can represent the central area of a spherical pellet that is not irradiated radially, but rather through an entrance hole allowing the laser beam to almost impact its inner surface tangentially (Pisarczyk et al 2018 Sci. Rep. 8 17 895). In the reported experiment, snail targets of various diameters were irradiated by linearly or circularly polarized radiation of a Prague asterix laser system (PALS) iodine laser delivering ∼500 J, 350 ps and 1.315 μm pulses on targets. Three-frame complex interferometry demonstrated that plasma is generated on the entire inside and outside surfaces of the snail target, start...

Research paper thumbnail of Influence of the magnetic field on properties of hot electron emission from ablative plasma produced at laser irradiation of a disc-coil target

Plasma Physics and Controlled Fusion

Optical generators of strong magnetic fields based on the laser-driven-coil target (LDCT) concept... more Optical generators of strong magnetic fields based on the laser-driven-coil target (LDCT) concept are considered to be useful tools for studies of magnetized plasmas, in particular for the study of implosion of magnetized fusion targets in inertial fusion research and astrophysical applications. This paper presents results of the research directed at investigation of the plasma properties in a laser-induced magnetic field. In the experiment carried out on the kilojoule PALS laser facility, a generator of the magnetic field was a disc-coil (DC) target composed of a Cu disk coupled to a single-turn coil irradiated by a 1ω laser beam with an energy of 500 J. The attention was focused on examining the influence of the magnetic field on properties of the hot electron (HE) flux emitted from the front surface of the irradiated target. The 3-frame complex interferometry and 4-frame X-ray camera combined with the measurements of the HE population and energy using a multi-channel magnetic ele...

Research paper thumbnail of Improvement of Diagnostics for Measurement of Multi-MeV Ions Produced in Deuterium Gas-Puff Z-Pinch

APS Division of Plasma Physics Meeting Abstracts, 2019

Research paper thumbnail of Measurements of Early-Time Plasma Evolution in the Hawk Dense Plasma Focus

2018 IEEE International Conference on Plasma Science (ICOPS), 2018

The 650 kA Hawk pulsed power generator at NRL has been configured as a fast (1.2 μs), high in duc... more The 650 kA Hawk pulsed power generator at NRL has been configured as a fast (1.2 μs), high in ductance (607 nH) driver for a dense plasma focus load. The current pulse is initiated in a radially injected deuterium plasma. This plasma is accelerated through a coaxial region, and pinches onto neutral deuterium injected axially by a gas-puff valve. A ribbon beam interferometer is used to diagnose the plasma in the coaxial region at several radii, providing time resolved electron density measurements through the initiation and axial run-down phases of the implosion. We present interferometry results alongside imaging, spectroscopic, electrical, and radiation measurements that track the evolution of the imploding current sheath.

Research paper thumbnail of Organized Structeres, Magnetic Reconnections and Acceleration of Fast Beams in Plasma-Focus Fusion Plasma

2018 IEEE International Conference on Plasma Science (ICOPS), 2018

Fusion plasmas produced in tokamaks, inertial-fusion experiments with powerful lasers, and z-pinc... more Fusion plasmas produced in tokamaks, inertial-fusion experiments with powerful lasers, and z-pinch discharges, deal with similar questions concerning the generation of high energy beams of charge particles, similar to those emitted from plasmas in Universe1-3. In all cases, a fast release of magnetic energy during magnetic reconnections of various organized structures is often considered. Dense plasmas, which are produced in plasma-focus discharges, have some advantages in solving this problem, since they have very convenient parameters for complementary diagnostics with relative simple temporal-, spatial- and spectral-resolution. The described experimental research on DD fusion reactions was performed at the current intensity of about 1 MA and the total neutron yield of about 1010 per shot. A multi-frame interferometry system, scintillation detectors, as well as X -ray and corpuscular diagnostic equipment - made it possible to study the evolution of toroidal- and plasmoidal-structures, which were formed by closed currents with poloidal and toroidal components in filamentary forms. The production of hard X -rays and fusion neutrons correlated with the formation and decay of plasmoids4. The gained knowledge about evolution of the ordered structures, transformations of currents and magnetic fields - can be an inspiration for researchers of the tokamak- and laser-fusion as well as for astrophysicists community.

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

New Journal of Physics, 2020

Acceleration of ions to multi-MeV energies is investigated in various plasma devices to better un... more 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 × 1013 and 1011, respectively. Accelerated deuterons produced one 20 ns (full width at hal...

Research paper thumbnail of Neutron fluence distribution in experiments with 3 MA deuterium gas-puff z-pinch

Physics of Plasmas, 2020

Deuterium gas-puff z-pinches are very efficient laboratory sources of neutron pulses. Using a nov... more 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 5.6×1012 is reached. At the same time, a very broad neutron energy spectrum up to energies on the order of tens of MeV is observed. In these experiments, the neutrons are produced not only by the D(d,n)3He (DD) nuclear reaction but also by reactions of multi-MeV deuterons with the experimental hardware. The angular distribution of the neutron fluence and dependence of the fluence on the distance from the z-pinch are measured using neutron activation diagnostics. By this method, a number of produced non-DD neutrons and anisotropy of DD neutron emission are evaluated.

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

Plasma Physics and Controlled Fusion, 2020

Research paper thumbnail of Target current: a useful parameter for characterizing laser ablation

Laser and Particle Beams, 2017

A current flowing between the ground and target exposed to the nanosecond laser radiation is anal... more 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.

Research paper thumbnail of Electromagnetic pulse (EMP) radiation by laser interaction with a solid H2 ribbon

Physics of Plasmas, 2017

The electromagnetic pulses (EMPs) generated during the interaction of a focused 1.315-μm sub-nano... more The electromagnetic pulses (EMPs) generated during the interaction of a focused 1.315-μm sub-nanosecond laser pulse with a solid hydrogen ribbon were measured. The strength and temporal characteristics of EMPs were found to be dependent on the target density. If a low density target is ionized during the interaction with the laser, and the plasma does not physically touch the target holder, the EMP is weaker in strength and shorter in time duration. It is shown that during the H2 target experiment, the EMP does not strongly affect the response of fast electronic devices. The measurements of the EMP were carried out by Rohde&Schwarz B-Probes, particularly sensitive in the frequency range from 30 MHz and 1 GHz. Numerical simulations of resonant frequencies of the target chamber used in the experiment at the Prague Asterix Laser System kJ-class laser facility elucidate the peaked structure of EMP frequency spectra in the GHz domain.

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

Physics of Plasmas, 2017

The paper concerns important differences in the evolution of plasma column structures during the ... more 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.

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

Plasma Physics and Controlled Fusion, 2017

The current balancing the target charging and the emission of transient electromagnetic pulses (E... more The current balancing the target charging and the emission of transient electromagnetic pulses (EMP) driven by the interaction of a focused 1.315 μm 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.

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

Journal of Instrumentation, 2016

Recent experiments at the laser facility PALS focused on the laser driven fusion of deuterons are... more 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 3× 1016 W cm−2. In the reported experiments fast fusion neutrons with energy up to 16 MeV were produced through 7Li(d, n)8Be and 11B(d, n)12C 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 2H(d, n)3He reaction increased by a factor of about 5, from 4× 108 to 2× 109. 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.

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

Physics of Plasmas, 2015

This paper presents the results of the research of the influence of compressed neon, injected by ... more 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.

Research paper thumbnail of Acceleration of Hydrogen Ions up to 30 MeV and Generation of 3x10 12 Neutrons in Megaampere Deuterium Gas-Puff Z-Pinch

The peak neutron yield from DD reactions reached Y n = (2.9 ± 0.3) × 10 12 at 100 µg/cm linear ma... more The peak neutron yield from DD reactions reached Y n = (2.9 ± 0.3) × 10 12 at 100 µg/cm linear mass density of deuterium, 700 ns implosion time and 2.7 MA current. Such a neutron yield means that the scaling law of deuterium z-pinches Y n ∝ I 4 was extended to 3 MA currents. The further increase of neutron yields up to (3.7 ± 0.4) × 10 12 was achieved by placing a deuterated polyethylene catcher onto the axis. Maximum neutron energies of 15 and 22 MeV were observed by radial and axial nToF detectors, respectively. A stack of CR-39 track detectors showed up to 40 MeV deuterons (or 30 MeV protons) on the z-pinch axis. Since the energy input into plasmas was 70 kJ, the number of DD neutrons per one joule of stored plasma energy exceeded the value of 5 × 10 7. This value implies that deuterium gas-puff z-pinches belong to the most efficient plasma-based sources of DD neutrons.

Research paper thumbnail of Long-Implosion-Time Z-pinch Experiments with Deuterium Gas-Puffs on the GIT-12 Generator

Experiments with deuterium triple shell gas-puffs have been carried out on the GIT-12 generator a... more Experiments with deuterium triple shell gas-puffs have been carried out on the GIT-12 generator at the IHCE in Tomsk. Outer, middle, and inner nozzle diameters were 160 mm, 80 mm and 30 mm, respectively. The influence of the mass of deuterium shells on neutron emission times, neutron yields and neutron spectra was studied. The linear mass density of deuterium varied between 50 and 270 μg/cm. Gas puffs imploded onto the axis before the peak of a generator current at 700-1100 ns. The first neutron peak occurred during the stagnation. Most of the neutrons were emitted during the second neutron pulse after the development of instabilities. In lower mass gas puffs, neutron energies of up to 4.4 MeV gave the evidence of 1 MeV deuterons. The peak neutron yield from D(d,n)^3He reactions reached 3x10^11 on a current level of 2.5 MA. Secondary DT neutrons were measured by BDS-10000 bubble detectors. An average neutron yield ratio Y>10 MeV/Y2.5 MeV exceeded (6±3)x10-4. Ne-Ne-D2 and Ne-D2-D2...

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

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

Review of Scientific Instruments, 2014

Measurements of the return-current flowing through a solid target irradiated with the sub-nanosec... more 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.