[Show abstract][Hide abstract] ABSTRACT: The effect of laser intensity on characteristics of the plasma ablated from a low-Z (CH) planar target irradiated by a 250 ps, 0.438 μm laser pulse with the intensity of up to 10 16 W/cm 2 as well as on parameters of the laser-driven shock generated in the target for various scale-lengths of preformed plasma was investigated at the kilojoule Prague Asterix Laser System (PALS) laser facility. Characteristics of the plasma were measured with the use of 3-frame interferometry, ion diagnostics, an X-ray spectrometer, and K α imaging. Parameters of the shock generated in a Cl doped CH target by the intense 3ω laser pulse were inferred by numerical hydrodynamic simulations from the measurements of craters produced by the shock in the massive Cu target behind the CH layer. It was found that the pressure of the shock generated in the plastic layer is relatively weakly influenced by the preplasma (the pressure drop due to the preplasma presence is ∼10–20%) and at the pulse intensity of ∼10 16 W/cm 2 the maximum pressure reaches ∼80–90 Mbar. However, an increase in pressure of the shock with the laser intensity is slower than predicted by theory for a planar shock and the maximum pressure achieved in the experiment is by a factor of ∼2 lower than predicted by the theory. Both at the preplasma absence and presence, the laser-to-hot electrons energy conversion efficiency is small, ∼1% or below, and the influence of hot electrons on the generated shock is expected to be weak.
[Show abstract][Hide abstract] ABSTRACT: This paper reports on properties of a plasma formed by sequential action of two laser beams on a flat target, simulating the conditions of shock-ignited inertial confinement fusion target exposure. The experiments were performed using planar targets consisting of a massive copper (Cu) plate coated with a thin plastic (CH) layer, which was irradiated by the 1ω PALS laser beam (
= 1.315 μm) at the energy of 250 J. The intensity of the fixed-energy laser beam was scaled by varying the focal spot radius. To imitate shock ignition conditions, the lower-intensity auxiliary 1ω beam created CH-pre-plasma which was irradiated by the main beam with a delay of 1.2 ns, thus generating a shock wave in the massive part of the target. To study the parameters of the plasma treated by the two-beam irradiation of the targets, a set of various diagnostics was applied, namely: (i) Two-channel polaro-interferometric system irradiated by the femtosecond laser (~40 fs), (ii) spectroscopic measurements in the X-ray range, (iii) two-dimensional (2D)-resolved imaging of the K
line emission from Cu, (iv) measurements of the ion emission by means of ion collectors, and (v) measurements of the volume of craters produced in a massive target providing information on the efficiency of the laser energy transfer to the shock wave. The 2D numerical simulations have been used to support the interpretation of experimental data. The general conclusion is that the fraction of the main laser beam energy deposited into the massive copper at two-beam irradiation decreases in comparison with the case of pre-plasma. The reason is that the pre-formed and expanding plasma deteriorates the efficiency of the energy transfer from the main laser pulse to a solid part of the targets by means of the fast electrons and the wave of an electron thermal conductivity.
No preview · Article · Jun 2015 · Laser and Particle Beams
[Show abstract][Hide abstract] ABSTRACT: The purpose of this paper is to present the newly-opened High Power Laser Laboratory (HPLL) at the Institute of Plasma Physics and Laser Microfusion (IPPLM). This article describes the laser, the main laboratory accessories and the diagnostic instruments. We also present preliminary results of the first experiment on ion and X-ray generation from laser-produced plasma that has been already performed at the HPLL.
No preview · Article · Jun 2015 · Nukleonika -Original Edition-
[Show abstract][Hide abstract] ABSTRACT: This review article describes apparatus for ion and X-ray diagnostics, which were used in experimental studies of laser-produced plasmas performed by the IPPLM's team in collaboration with other researchers at IPPLM and PALS Research Centre in Prague (the Czech Republic). The investigations of expanding laser-produced plasma properties in dependence on laser beam parameters were done by means of ion diagnostics devices: ion collectors (ICs), cylindrical ion energy analyzer (IEA) and the mass spectrograph of the Thomson type. At IPPLM, different types of detectors have been developed for measurement of X-ray emission. Properties of laser-produced beams of ions and X-ray radiation were analysed in the cooperative experiments performed with the use of a high-energy iodine laser PALS at the PALS Research Centre ASCR in the Czech Republic and the low-energy repetitive laser at IPPLM.
No preview · Article · Apr 2015 · Radiation Effects and Defects in Solids
[Show abstract][Hide abstract] ABSTRACT: Among various methods for the acceleration of dense plasmas the mechanism called laser-induced cavity pressure acceleration (LICPA) is capable of achieving the highest energetic efficiency. In the LICPA scheme, a projectile placed in a cavity is accelerated along a guiding channel by the laser-induced thermal plasma pressure or by the radiation pressure of an intense laser radiation trapped in the cavity. This arrangement leads to a significant enhancement of the hydrodynamic or electromagnetic forces driving the projectile, relative to standard laser acceleration schemes. The aim of this paper is to review recent experimental and numerical works on LICPA with the emphasis on the acceleration of heavy plasma macroparticles and dense ion beams. The main experimental part concerns the research carried out at the kilojoule sub-nanosecond PALS laser facility in Prague. Our measurements performed at this facility, supported by advanced two-dimensional hydrodynamic simulations, have demonstrated that the LICPA accelerator working in the long-pulse hydrodynamic regime can be a highly efficient tool for the acceleration of heavy plasma macroparticles to hyper-velocities and the generation of ultra-high-pressure (>100 Mbar) shocks through the collision of the macroparticle with a solid target. The energetic efficiency of the macroparticle acceleration and the shock generation has been found to be significantly higher than that for other laser-based methods used so far. Using particle-in-cell simulations it is shown that the LICPA scheme is highly efficient also in the short-pulse high-intensity regime and, in particular, may be used for production of intense ion beams of multi-MeV to GeV ion energies with the energetic efficiency of tens of per cent, much higher than for conventional laser acceleration schemes.
Full-text · Article · Jan 2015 · Plasma Physics and Controlled Fusion
[Show abstract][Hide abstract] ABSTRACT: We report the experiment conducted on the Prague Asterix Laser System (PALS) laser facility dedicated to make a parametric study of the laser–plasma interaction under the physical conditions corresponding to shock ignition thermonuclear fusion reactions. Two laser beams have been used: the auxiliary beam, for preplasma creation on the surface of a plastic foil, and the main beam to launch a strong shock. The ablation pressure is inferred from the volume of the crater in the Cu layer situated behind the plastic foil and by shock breakout chronometry. The population of fast electrons is analyzed by Kα emission spectroscopy and imaging. The preplasma is characterized by three-frame interferometry, x-ray spectroscopy and ion diagnostics. The numerical simulations constrained with the measured data gave a maximum pressure in the plastic layer of about 90 Mbar.
[Show abstract][Hide abstract] ABSTRACT: Ion emission from plasmas obtained by the use of a 600 fs, 36 mJ KrF laser operating at 248 nm was measured and analysed for a variety of targets at different laser intensities. The intensity was set by changing the distance between the focusing lens and the target. It was found that the ions emitted originate from impurities and ions from the bulk of the target can be produced only in the subsequent shots. Proton emission was identified from some targets, but the energy of the protons was low (less than 12 keV). A new silicon carbide semiconductor detector proved to be applicable for the collection of the ions.
[Show abstract][Hide abstract] ABSTRACT: The goal of this contribution is to present time-resolved optical spectroscopy studies of laser ablation of the Mo target with similar to 3.5 ns, 0.4 J pulses delivered by the Nd-YAG laser system at 1.06 mu m. The sample was placed in a vacuum chamber under 5x10(-5) mbar pressure and irradiated, with power densities varied up to 22.7 GW cm(-2). The ion emission from the plasma plume was measured using an electrostatic ion energy analyzer (IEA) and ion collector, which allowed us to estimate the ion kinetic energy and charge independent of the applied power densities. The signal collected by the IEA indicated the presence of molybdenum ions up to eight-ion charge. Simultaneously after the ion emission, the optical spectra acquired within 2 mu s of exposure time were observed in the wavelength range from 200 to 1000 nm with a Mechelle 5000 spectrometer equipped with an iCCD (iStar) detector. The plasma electron temperature was estimated from a Boltzmann plot based on the registered spectra as well as from the ion measurements.
[Show abstract][Hide abstract] ABSTRACT: A space-resolved charge density of ions is derived from a time-resolved current of ions emitted from laser-produced plasma and expanded into the vacuum along collision-free and field-free paths. This derivation is based on a similarity relationship for ion currents with “frozen” charges observed at different distances from the target. This relationship makes it possible to determine a map of ion charge density at selected times after the laser plasma interaction from signals of time-of-flight detectors positioned at a certain distance from the target around a target-surface normal. In this work, we present maps of the charge density of ions emitted from Cu and polyethylene plasmas. The mapping demonstrates that bursts of ions are emitted at various ejection angles ϕ
with respect to the target-surface normal. There are two basic directions ϕ
1 and ϕ2, one belonging to the fastest ions, i.e., protons and carbon ions, and the other one to the slowest ions being a part of each plasma plume.
Full-text · Article · Mar 2014 · Laser and Particle Beams
[Show abstract][Hide abstract] ABSTRACT: The aim of this paper is to describe the newly-opened High Power Laser Laboratory (HPLL) at the Institute of Plasma Physics and Laser Microfusion (IPPLM) and presents its research possibilities in terms of the laser source and the available diagnostics. The interactions of the ultra-short laser pulses of femto to pico second duration and energies of up to 1 J with solid-state targets leads to very distinguish phenomena which can be used for investigation of exotic states of matter and to apply them for numerous technological purposes. in this goal the application of sophisticated and especially designed diagnostic systems is also needed. As the effects of interactions include the broad range of processes as acceleration of fast ions and electrons, x-rays generation and solid material modification in terms of its mechanical, physical and optical properties the research needs to use both online plasma diagnostics and the methods of post-mortem material research characterization methods. The paper presents a brief description of the laser system, the interaction vacuum chambers and the available diagnostics as well as the scientific investigation trends which can be picked up at the HPLL at the IPPLM.
No preview · Article · Jan 2014 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: Laser-induced cavity pressure acceleration (LICPA) is a novel scheme of acceleration of dense matter having a potential to accelerate plasma projectiles with the energetic efficiency much higher than the achieved so far with other methods. In this scheme, a projectile placed in a cavity is irradiated by a laser beam introduced into the cavity through a hole and accelerated along a guiding channel by the thermal pressure created in the cavity by the laser-produced plasma or by the photon pressure of the ultraintense laser radiation trapped in the cavity. This paper summarizes briefly the main results of our recent LICPA studies, in particular, experimental investigations of ion beam generation and heavy macroparticle acceleration in the hydrodynamic LICPA regime (at moderate laser intensities similar to 10(15)W/cm(2)) and numerical, particle-in-cell (PIC) studies of production of ultraintense ion beams and fast macroparticles using the photon pressure LICPA regime (at high laser intensities > 10(20) W/cm(2)). It is shown that in both LICPA regimes the macroparticles and ion beams can be accelerated much more efficiently than in other laser-based acceleration scheme commonly used and the accelerated plasma/ion bunches can have a wide variety of parameters. It creates a prospect for a broad range of applications of the LICPA accelerator, in particular in such domains as high energy density physics, ICF research (ion fast ignition, impact ignition) or nuclear physics.
No preview · Article · Jan 2014 · Journal of Physics Conference Series
[Show abstract][Hide abstract] ABSTRACT: Efficiency of the laser radiation energy transport into the shock wave generated in layered planar targets (consisting of massive Cu over coated by thin CH layer) was investigated. The targets were irradiated using two laser pulses. The 1ω pulse with the energy of ̃50 J produced a pre-plasma, imitating the corona of the pre-compressed inertial confinement fusion target. The second main pulse used the 1ω or 3ω laser harmonics with the energy of ̃200 J. The influence of the pre-plasma on parameters of the shock wave was determined from the crater volume measurements and from the electron density distribution measured by 3-frame interferometry. The experimental results show that the energy transport by fast electrons provides a definite contribution to the dynamics of the ablative process, to the shock wave generation, and to the ablation pressure in dependence on the target irradiation conditions. The strong influence of the pre-plasma on the investigated process was observed in the 1ω case. Theoretical analysis supports the explanation of experimental results.
No preview · Article · Dec 2013 · Physics of Plasmas
[Show abstract][Hide abstract] ABSTRACT: Shock ignition (SI) is an appealing approach in the inertial confinement scenario for the ignition and burn of a
pre-compressed fusion pellet. In this scheme, a strong converging shock is launched by laser irradiation at an
intensity Iλ2 >1015 Wcm−2 μm2 at the end of the compression phase. In this intensity regime, laser–plasma
interactions are characterized by the onset of a variety of instabilities, including stimulated Raman scattering,
Brillouin scattering and the two plasmon decay, accompanied by the generation of a population of fast electrons. The effect of the fast electrons on the efficiency of the shock wave production is investigated in a series of dedicated experiments at the Prague Asterix Laser Facility (PALS). We study the laser–plasma coupling in a SI relevant regime in a planar geometry by creating an extended preformed plasma with a laser beam at ∼7 × 1013 Wcm−2 (250 ps, 1315 nm). A strong shock is launched by irradiation with a second laser beam at intensities in the range 1015–1016 Wcm−2 (250 ps, 438 nm) at various delays with respect to the first beam. The pre-plasma is characterized using x-ray spectroscopy, ion diagnostics and interferometry. Spectroscopy and calorimetry of the backscattered radiation is performed in the spectral range 250–850 nm, including (3/2)ω, ω and ω/2 emission. The fast electron production is characterized through spectroscopy and imaging of the Kα emission. Information on the shock pressure is obtained using shock breakout chronometry and measurements of the craters produced by the shock in a massive target. Preliminary results show that the backscattered energy is in the range 3–15%, mainly due to backscattered light at the laser wavelength (438 nm), which increases with increasing the delay between the two laser beams. The values of the peak shock pressures inferred from the shock breakout times are lower than expected from 2D numerical simulations. The same simulations reveal that the 2D effects play a major role in these experiments, with the laser spot size comparable with the distance between critical and ablation layers.
Full-text · Article · Dec 2013 · Plasma Physics and Controlled Fusion
[Show abstract][Hide abstract] ABSTRACT: A scheme to enhance the target foil velocity has been investigated for a
direct drive inertial fusion target. Polymer PVA (polyvinyl alcohol or
(C2H4O)n) target foils of thickness
15-20 μm were used in plain form and also embedded with gold in the
nano-particle (Au-np) or micro-particle (Au-mp) form. Nano-particles
were of 20-50 nm and micro-particles of 2-3 μm in size. 17% higher
target velocity was measured for foils embedded with nano-particle gold
(Au-np) as compared to targets embedded with micro-particles gold
(Au-mp). The weight of gold in both cases was in the range 40-55% of the
full target weight (atomic percentage of about 22%). Experiments were
performed with the single beam of the Prague Asterix Laser System (PALS)
at 0.43 μm wavelength (3ω of the fundamental wavelength), 120
Joule energy and 300 psec pulse duration. Laser intensity on the target
was about 1015 W/cm2. A simple model has been
proposed to explain the experimental results.
No preview · Article · Nov 2013 · The European Physical Journal Conferences
[Show abstract][Hide abstract] ABSTRACT: 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).
[Show abstract][Hide abstract] ABSTRACT: Generation of ion fluxes in the laser-induced cavity pressure acceleration (LICPA) scheme is investigated by the time-of-flight method and compared with the one in the conventional laser-planar target interaction scheme. It is shown that the ion current density and intensity of the ion flux produced in the LICPA scheme from CD2 foil target irradiated by a 0.3-ns laser pulse of intensity ∼1014–1015 W/cm2 are by an order of magnitude higher and the mean and maximum ion energies by a factor 4–5 higher than those for the conventional scheme.
[Show abstract][Hide abstract] ABSTRACT: The effect of preformed plasma on a laser-driven shock produced in a planar target at the conditions relevant to the shock ignition scenario of ICF was investigated at the kilojoule PALS laser facility. Characteristics of the preformed plasma were controlled by the delay ∆t between the auxiliary beam (1ω, 7×10 13 W/cm 2) and the main 3ω, 250 ps laser pulse of intensity up to 10 16 W/cm 2 , and measured with the use of 3-frame interferometry, ion diagnostics, an X-ray spectrometer and K α imaging. Parameters of the shock produced in a CH(Cl) target (25 µm or 40 µm thick) by the intense 3ω laser pulse with energy ranging between 50 J and 200 J were determined by measuring the craters produced by the shock in a massive Cu target behind the layer of plastic. The volume and the shape of these craters was found to depend rather weakly on the preplasma thickness, which implies the same is true for the total energy of shocks and pressure generated by them. From the comparison of the measured crater parameters with those obtained in 2D simulations using the PALE code, it was estimated that for I 3ω ≈ 10 16 W/cm 2 the pressure at the rear (non-irradiated) side of the 25-µm plastic layer reaches about 100 Mbar.
[Show abstract][Hide abstract] ABSTRACT: The efficiency of the laser energy conversion to a shock wave has been investigated in solid targets irradiated by a single or two consecutive laser beams. The first laser pulse was used to produce the plasma simulating conditions relevant to shock ignition approach. One-and two-layer planar targets (bulk Al and Cu alternatively covered by a thin CH layer) were used. The laser provided a 250 ps pulse within the intensity range of 1-50 PW/cm 2 at the first and third harmonics with wavelengths of 1.315 and 0.438 μm, respectively. Three-frame interferometry and measurements of crater parameters were used as the main diagnostics. The contribution of fast electrons to ablation and the laser energy conversion into shock wave have been investigated for different conditions of the target irradiation, including the pre-plasma presence. 2D numerical simulations and theoretical analysis were carried out to support explanation of experimental results.