[Show abstract][Hide abstract] ABSTRACT: In our earlier papers it was demonstrated that the plasma pressure
decreases with the growing atomic number of the target material. In this
context a question arose about the possibility to collimate the Al
plasma outflow by using the plastic plasma as a compressor. For that
purpose a plastic target with an Al cylindrical insert of 400 μm in
diameter was used. The experiment was carried out at the PALS laser
facility. The laser provided a 250 ps (FWHM) pulse with the energy of
130 J at the third harmonic frequency (λ3 = 0.438
μm). The focal spot diameters (ΦL) 800, 1000, and 1200
μm ensured predominance of the plastic plasma, its transversal
extension being large enough for the effective Al plasma compression. To
study the Al plasma stream propagation and its interaction with the
plastic plasma, a 3-frame interferometric system and 4-frame x-ray
camera were used. The information on distribution of electron
temperature in the outflowing Al plasma was provided by x-ray
spectroscopy. The experimental results reported in the paper are
discussed by virtue of a simple theoretical analysis.
Preview · Article · Nov 2013 · The European Physical Journal Conferences
[Show abstract][Hide abstract] ABSTRACT: form only given. The paper is aimed at the explanation of mechanisms responsible for laser radiation absorption by a planar massive target made of Al. Absorption mechanisms of laser radiation have been studied in experiments at Prague Asterix Laser System (PALS). The investigations were performed for the first harmonic of laser radiation, four focal spot radii (40, 80, 120, and 160 μm) and the laser pulse duration of 250 ps (FWHM) at energy of 290 J. For given target irradiation conditions, the laser intensity was varied in a range of 2.6×1015-4.1×1016 Wcm-2. The two laser beam incidence were used: normally to the target surface and at the 45° angle. Additionally, the laser beam incident normally was polarized linearly and circularly. A three-frame interferometry and measurement of crater parameters by a wax-replica technique were used as the main diagnostic tools. Two different mechanisms of laser radiation absorption were distinguished: resonance and inverse bremsstrahlung. Besides, the ratio of total electron number just after the laser pulse end to the crater volume has proved a great role of fast electrons in the laser energy transfer into the target. Investigations have also shown that the oblique incidence of laser beam reduces the resonance absorption of laser radiation.
[Show abstract][Hide abstract] ABSTRACT: The calculations and analysis of the target compression state are reported for the HiPER facility under deviation of the baseline target irradiation conditions from the completely symmetric conditions considered earlier. The irradiation asymmetry readily arises at a small number of irradiating laser beams (or the directions of irradiation, for example, two or 8-20 directions) if the targets are used in a thermonuclear reactor where the number of beams is limited.
The calculations have been taken by the scheme proposed earlier, which includes plotting of the irradiation maps and histograms, 1D- and 2D simulations of the target irradiation and compression. The calculations of the foam absorber targets have been compared to the experiments on the plane target irradiation at the LIL facility, where the absorber size and the irradiation conditions are in agreement with the conditions necessary for the HiPER facility.
No preview · Article · Aug 2010 · Journal of Physics Conference Series
[Show abstract][Hide abstract] ABSTRACT: One possibility of controlling the parameters of the plasma streams in the inner cavities of laser thermonuclear targets is by using an external magnetic field. In the present paper, the authors consider the theory of magnetically controlling plasma streams in inner cavities of laser thermonuclear targets, and propose a solution to one of the problems of increasing the operating efficiency of targets with internal laser-radiation input -- the problem of filling the openings for the entry of the laser radiation by restraining the plasma streams during the laser pulse with the aid of an external transverse magnetic field. It is shown that a magnetic field of several MG suffices for this purpose. 9 refs.
No preview · Article · Jan 2009 · Journal of Soviet Laser Research
[Show abstract][Hide abstract] ABSTRACT: In the paper investigations of ablative plasma configurations for three different target materials (plastic, Al and Cu) and of plasmas generated from joints of plastic-Cu and Al-Cu are presented. The experiment was carried out at the PALS iodine laser system, with the third harmonic beam of the pulse duration of 250 ps (FWHM). The beam energies varied in the range of 75±2 J, the focal spot radius on the target surface was set to 300 μm with the focal point position inside the target. The experiment has shown that the plasma strongly transforms the laser intensity distribution, which, vice versa, results in changing the plasma characteristics. Depending on the target material different ablative plasma configurations can be created. It has been also confirmed that the ring form of the target irradiation profile resulting from the laser beam-plasma interaction is a necessary condition for the plasma jet creation by a single laser beam. In the case of joint targets, remarkable obliquely propagating jet-like plasma outflows were observed.
[Show abstract][Hide abstract] ABSTRACT: Different designs of a green house target (GHT) were considered at 2 MJ laser pulse energy, in which the thermonuclear gain G achieved ~20-30 in one-dimensional calculations. The GH targets were designed to attain a symmetrical compression and efficient thermonuclear burning of a target irradiated by a low number of laser beams (N=2, 4, 6, 8 ... ) by using a low-density foam-like absorber. But as compared to the earlier studied target designs, where the value of gain G achieved ˜ 8, the newly developed schemes are more risky, less reliable, and less experimentally verified. In the calculations, value G is increased as one employs a longer laser pulse for compression, the greater A=R0/Delta R0, the conversion ratio R0/R_min, and the lesser value alpha=p/pF. It seems that all these changes correspond to a less stable regime of operation. A sensitivity of results to the elements of uncertainty in the physics of processes is discussed.
No preview · Article · Jun 2006 · Journal de Physique IV (Proceedings)
[Show abstract][Hide abstract] ABSTRACT: We present the results of experiments on the short-term irradiation of a solid material by a laser beam. The data testify to a rise in efficiency of the energy transfer from the laser pulse to a shock wave due to the fast-electron energy transfer. The experiments were performed with massive aluminium targets on the PALS iodine laser, whose pulse duration (0.4 ns) was much shorter than the time of shock decay and crater formation in the target (50-200 ns). The irradiation experiments were carried out using the fundamental laser harmonic (1.315 m) with an energy of 360 J. The greater part of the experiments were performed for the radiation intensity exceeding 10¹ W cm², which corresponded to the efficient generation of fast electrons under the conditions where the relatively long-wavelength iodine-laser radiation was employed. The irradiation intensity was varied by varying the laser beam radius for a specified pulse energy. (interaction of laser radiation with matter. laser plasma)
No preview · Article · May 2006 · Quantum Electronics
[Show abstract][Hide abstract] ABSTRACT: The results of investigations are presented which are concerned with laser radiation absorption in a target, the plasma state of its ablated material, the energy transfer to the solid target material, the characteristics of the shock wave and craters on the target surface. The investigation involved irradiation of a planar target by a subnanosecond plasma-producing laser pulse. The experiments were carried out with massive aluminium targets using the PALS iodine laser, whose pulse duration (0.4 ns) was much shorter than the shock wave attenuation and on-target crater formation times (50-200 ns). The investigations were conducted for a laser radiation energy of 100 J at two wavelengths of 0.438 and 1.315 Î¼m. For a given pulse energy, the irradiation intensity was varied in a broad range (10Â¹Â³-10Â¹â¶ W cmâ»Â²) by varying the radius of the laser beam. The efficiency of laser radiation-to-shock energy transfer was determined as a function of the intensity and wavelength of laser radiation; also determined were the characteristics of the plasma plume and the shock wave propagating in the solid target, including the experimental conditions under which two-dimensional effects are highly significant. (invited paper)
No preview · Article · Nov 2004 · Quantum Electronics
[Show abstract][Hide abstract] ABSTRACT: Experimental, theoretical, and numerical results of investigations of the iodine laser interaction with single and double
targets (consisting of an Al foil placed in front a massive Al slab and separated by a certain gap) were employed. Experiments
were performed with the use of the first harmonic of laser radiation with parameters as follows: laser energy in the range
of 100 ÷ 400 J, pulse duration of 0.4 ns and focal spot diameter of 250 μm. Velocities of accelerated foils and electron density
distributions of plasma streams were determined by means of 3-frame interferometry. Shapes and volumes of craters were obtained
employing crater replica technology and microscopy measurement. To interpret the experimental results the theoretical model
of plasma ablation and shock wave formation as well as the two-dimensional Lagrangian hydrodynamics code were used.
No preview · Article · Mar 2004 · Czechoslovak Journal of Physics
[Show abstract][Hide abstract] ABSTRACT: Efficient energy transfer and smoothing effect in laser-irradiated polystyrene foam targets have been observed in preliminary experiments on the PALS iodine laser facility. A theory of laser light absorption region formation and ablation pressure generation in laser-produced plasma of porous matter has been developed and applied for discussion of the results obtained. In particular, two stages of homogenization of the porous matter, important for comprehension of the anomalously high absorption of laser radiation in supercritical foam matter, have been identified: the first, a considerably fast stage of partial homogenization, followed by a much slower second stage, leading to a uniform medium.
Full-text · Article · May 2003 · Fusion Science and Technology
[Show abstract][Hide abstract] ABSTRACT: The possibility of efficient and symmetric compression of a target with a low-density structured absorber by a few laser beams is considered. An equation of state is proposed for a porous medium, which takes into account the special features of the absorption of high-power nanosecond laser pulses. The open version of this target is shown to allow the use of ordinary Gaussian beams, requiring no special profiling of the absorber surface. The conditions are defined under which such targets can be compressed efficiently by only two laser beams (or beam clusters). Simulations show that for a 2.1-MJ laser pulse, a seven-fold gain for the target under study is achieved. (special issue devoted to the 80th anniversary of academician n g basov's birth)
No preview · Article · Feb 2003 · Quantum Electronics
[Show abstract][Hide abstract] ABSTRACT: This paper outlines the theoretical direct-ignition model of the pre-compressed thermonuclear material of an inertial fusion target under the action of a high-power pulse of light ions from a laser plasma. It is shown that plasma streams with parameters required for the ignition can be obtained from a plane target-generator, located separately from the fusion target upon its fast thermal explosion driven by a high-power laser pulse. This method of direct ignition implies the use of a fusion target whose design provides the supply of the igniting driver energy to the compressed thermonuclear material. This target may be a cylindrical target with partially open ends or a spherical target with one or two conic openings.
No preview · Article · Oct 2001 · Quantum Electronics
[Show abstract][Hide abstract] ABSTRACT: A two-dimensional model is proposed for describing plasma formation when a pulsed energy source acts on a planar layer of matter which either has free surfaces or is bounded on one or both sides by thermally insulating infinitely heavy walls with apertures for injecting radiation. Conditions are found for efficient heating of matter in the inner cavity of a target by a radiation or ion beam under conditions of minimal energy losses associated with hydrodynamic expansion of matter through a radiation-injection aperture. A version of a model is suggested for describing the formation of a plasma in a low-density absorber of the kind used in inertial-confinement thermonuclear fusion targets with internal injection of laser radiation. (interaction of laser radiation with matter. laser plasma)
No preview · Article · Dec 1998 · Quantum Electronics
[Show abstract][Hide abstract] ABSTRACT: Summary form only given, as follows. An experimental study of the radiation scattered by laser heating of low density foam targets is presented. The experiments were carried out on a laser facility with wavelength 0.53 μm, pulse duration 2.5 ns, focal spot diameter 15 μm, flux density on target surface ~5 10<sup>14</sup> W/cm<sup>2</sup>. The targets were prepared from porous polypropylene (CH)<sub>x</sub> with average density ~0.02 g/cm<sup>3</sup> and cell size ~50 μm. Both forward-, side- and back-scattered radiations including one created by the stimulated Brillouin scattering have been recorded, that enabled us to study the dynamics of the process of burning-through of the thick foam targets, the velocities of the plasma critical density motion as well as mass velocity of the plasma. The intensities of stimulated Brillouin scattering for the porous targets had the same value as for the solid ones (3-4% from laser density) but the spectral-temporal characteristics were quite different for these kinds of targets that confirms the different scattering properties and different ablation dynamics for the solid and the foam matter
[Show abstract][Hide abstract] ABSTRACT: An attempt is made to develop a physical foundation for the particle diagnostics of a laser plasma based on the scattering properties of the particles produced by fusion reactions. Monte Carlo numerical calculations have been carried out to find the yields of secondary fusion particles as functions of the plasma parameters. The effectiveness of using the characteristics of various secondary particles for diagnostic purposes is analyzed.
[Show abstract][Hide abstract] ABSTRACT: A unified optimization scheme is used in a numerical calculation of the dependences of the
thermonuclear yield of two-layer shell targets on the absorbed laser energy in the range 0.3–10 mJ
for lasers emitting radiation of wavelengths shorter than 1 μ.
No preview · Article · Jun 1985 · Soviet Journal of Quantum Electronics
[Show abstract][Hide abstract] ABSTRACT: Calculations are made of the compression ratio of the plasma of the simplest type of a shell target exposed to a laser pulse whose power increases with time in accordance with a power law and whose duration is shorter than the shell implosion time. It is found that as the exponent in the law describing the increase in the laser pulse power rises the entropy coupled into the compressed target material by the shock wave during motion of the shell decreases and consequently the final plasma density increases.
No preview · Article · Feb 1985 · Soviet Journal of Quantum Electronics
[Show abstract][Hide abstract] ABSTRACT: An investigation is made of the influence of a static magnetic field on the transfer of energy by
thermonuclear a particles in a laser plasma. A general solution and a number of particular
analytical solutions of the transport equation for a particles in a bounded plasma with a magnetic
field are constructed. It is shown that the compression of laser targets in a magnetic field of several
tens of kilogauss leads to a considerable increase (by a factor of 1.5?2) in the energy transferred to
the plasma by the a particles, and consequently to a reduction (by 20?40%) of the product of the
density and plasma radius necessary to achieve the physical threshold of a thermonuclear reaction.
No preview · Article · Aug 1984 · Soviet Journal of Quantum Electronics
[Show abstract][Hide abstract] ABSTRACT: A theoretical analysis is made of the kinetics of the ion composition of a laser plasma during its compression and expansion. It is shown that in a wide range of parameters of a laser plasma the ion composition of the matter in the compressed part of the plasma is quenched in. The effect is used as the basis of several diagnostic methods for the determination of the temperature or density of a plasma at the moment of its maximum compression, and for the investigation of the equation of state of a plasma and the stability of its compression.
No preview · Article · Apr 1983 · Soviet Journal of Quantum Electronics