The results of theoretical investigation of implosion and combustion of a direct-drive inertial confinement fusion (ICF) target as a shell with compound outer layer (ablator) intended to absorb laser radiation and produce the ablation pressure compressing the target are presented. It is proposed to supplement the solid ablator of conventional ICF target with an outer layer of a low-density porous substance with density corresponding to the nearly critical one of laser-produced plasma. It is shown that for a laser pulse with energy of 2-3 MJ, designed to ignite the deuterium-tritium reaction in modern experiments, the target with a compound ablator can provide a significant increase in fusion energy yield when the mass fraction of low-density component is in (10-15) % interval.

This paper presents results of computational and experimental studies of the evolution of turbulent mixing in three-layer gas systems with the development of hydrodynamic instabilities, in particular, the Richtmyer–Meshkov and Kelvin–Helmholtz instabilities, under the action of shock waves. One of the contact boundaries between gases is flat, while the other one has the form of a chevron. The numerical simulations are carried out both with and without initial perturbations of contact boundaries. It is shown that the roughness of the contact boundary significantly affects the width of the mixing zone.

This paper presents the experimental and numerical results of studying the growth dynamics of the deterministic and given initial perturbations defined in a certain way. The formation, growth, and further evolution of inhomogeneities of the contact boundary occurs due to the development of the Rayleigh–Taylor instability (RTI) at the gas-liquid interface, and in particular (in this study), the air-water interface. The significant difference in the densities of the selected substances leads to a noticeable slowdown in the dynamics of the Kelvin–Helmholtz instability (KHI), which is responsible for the formation of mushroom-like structures, and, as a result, to the longer growth of water jets and the later moment of their destruction and transition to mixing. In this study, a quantitative comparison of the physical data recorded on the original experimental setup, which is described in this paper, with the calculated data obtained using various numerical methods is carried out. The numerical modeling is based on a complete 2D hydrodynamic model for describing the dynamics of the development of the RTI. The surface tension (water-air) and viscosity (water or air) are neglected in this study. The parameters of the development of the instability measured in the experiment and found in the calculations indicate satisfactory agreement between the obtained data. The quantitative results presented in this study justify the use of the classical hydrodynamics model to describe the movements of liquid and gas observed in this experiment and the fairly accurate numerical implementation of the corresponding model in the difference methods used here. The investigation of the development of turbulent mixing depending on well-defined initial conditions and the new regularities of the laws of mixing of the media of different densities that arise in this case is an important element in the study.

Theoretical and computational results for the generation of a powerful shock wave with pressure behind the front exceeding a gigabar level in the half-space of a solid when the boundary layer is heated by a flux of laser-accelerated electrons are presented. The influence of the energy flux density of the heating stream, the characteristic initial energy and the electron spectrum on the characteristics of the shock wave is investigated. The main attention is paid to the generation of an extremely powerful shockwave, which can be applied in experiments to study the equation of state of matter. For this, the requirements for the parameters of a laser pulse that can ensure the propagation of a plane shock wave with a gigabar pressure when a substance is heated by a beam of laser-accelerated fast electrons, taking into account its divergence, are established. It is shown that one of the features of the propagation of a shock wave under the impact of a thermal piston heated by fast electrons consists in the radiation cooling of the peripheral region of the substance covered by the shock wave. An increase in the compression of matter due to radiation cooling leads to a multiple increase in the density of matter in the peripheral region of the shock wave compared to the density at its front. The final result of this work is to substantiate the use of shock waves driven by a beam of laser-accelerated electrons in a laboratory experiment to study the properties of matter, in particular, metals compressed to a density of several tens of g cc−1 under the action of gigabar pressure.

Results of experiments aimed at amplification of the pressure of laser-induced shock wave on the passage from low- to high-density target material via vacuum gap are presented. During the action of nanosecond laser pulse of terawatt power on plane composite targets comprising a layer of laser radiation absorber of low-density (0.01–0.025 g/cm3) spaced by vacuum gap from a layer of aluminum, the shock-wave velocity in aluminum reached 25–29 km/s and a pressure jump at the aluminum layer boundary was 1.2–1.5 times as large as that observed in experiments on the cumulative transition of laser-induced shock wave into a solid. The obtained experimental data are compared to results of the numerical calculations performed using hydrodynamic programs in which the shock-wave generation and propagation was modeled with allowance for the interaction of laser pulses with partly homogenized plasma of the porous material. Based on the results of experiments, numerical calculations, and their theoretical analysis, the efficiency of using low-density porous media in the targets intended for their equation of state investigations and inertial confinement fusion ignition is considered.

The study of the development of perturbations under the influence of various hydrodynamic instabilities, as well as the transition to turbulent mixing and turbulence, has been a subject of considerable interest over the past decades. This is primarily due to the importance of these phenomena in various fields of science and engineering. In addition, it should be noted that studies of the characteristics of turbulent flows, for example, have still not been completed. This is inspiring a great deal of interest in this topic, both in the sense of physical theory and in the sense of developing new approaches to the mathematical modeling of the corresponding problems. The capabilities of modern computer technology make it possible to carry out numerical experiments in two-dimensional and three-dimensional setups and analyze the features of the new numerical methods. Presently, numerous methods with many modifications are used in practice. This review focuses on the most promising among them.

With the construction of powerful laser facilities, research in high energy density physics has received a new push of the development due to the possibility of making experiments.One of the main directions during many years remains the study of the development of initial perturbations under the various hydrodynamic instabilities.Due to the development of modern diagnostic methods in the last decade, these phenomena were experimentally observed under conditions of high energy densities, which made it possible to verify the available numerical codes and also to obtain new data.The results of mathematical modeling of the development of Kelvin-Helmholtz instability in the conditions of irradiation of flat targets using an OMEGA laser facility are presented in this work.The vortex growth rate is compared with available experimental data.Taking into account the simplifications made in the numerical formulation of the problem, the various data are in satisfactory agreement with each other.The visualization of the flow made it possible to fully analyze its structure, determine the sizes of the characteristic vortices, and also reveal the differences between the 3D and 2D variants associated with the relaxation of the flow in transverse directions.The implementation of the visualization module is based on the use of VTK XML parallel format for storing data for analysis.

The influence of heating homogeneity violations in a laser thermonuclear target designed for shock ignition on the target compression and burning has been studied. We have performed our studies based on two-dimensional hydrodynamic simulations when modeling the target heating homogeneity violations due to various factors of symmetry violation of the target irradiation by a finite number of laser beams. The gains have been calculated at various perturbation amplitudes of the spatial distribution of absorbed energy in the target for two characteristic cases—low and high dominant perturbation modes. The first and second cases refer, respectively, to the factors of regular irradiation homogeneity violation due to a finite number of laser beams and a target offset from the focusing point and the factors of stochastic irradiation homogeneity violation related to laser beam energy imbalance, beam mispointing, and beam mistiming. We show that for a target designed for shock ignition the factors of regular irradiation homogeneity violation are much more dangerous than those for a spark ignition target.

The role of energy transfer by fast electrons, which is responsible for the positive effect of increasing the ablative pressure and the negative effect of preheating, on the implosion and thermonuclear gain of the target designed for shock ignition is investigated in comparison with the target designed for traditional spark ignition. On the base of one-dimensional hydrodynamic simulations with kinetic description of fast electron transfer it is shown, that depending on the characteristics of fast electron flux, in shock ignition target are manifested to varying degree both effects the positive and negative ones. This is a distinguishing feature of a shock ignition target compared to a traditional spark ignition target, in which only the negative effect of fast electron energy transfer takes place. In a shock ignition target up to temperatures of 50-60 keV, the positive effect is dominant and provides high gain. With an increase in the fast electron temperature, the role of the negative preheating effect increases, that ultimately leads to the ignition failure as temperature exceeding 90-100 keV.

The compression and burning of a fusion target ignited by a focused shock wave produced at the action of a time-profiled second harmonic laser pulse of a Nd laser have been calculated and theoretically studied. The main energy features of the shock ignition scheme have been considered. The use of the second harmonic radiation corresponds to a higher energy and a longer laser pulse necessary for ignition by this method compared to the use of the third harmonic radiation. Nevertheless, the method of ignition by the focused shock wave with the second harmonic radiation makes it possible to reach the fusion target gain that is two or three times higher than that at the traditional spark ignition with the laser pulse energy higher than in the former case by a factor of 1.5. The numerical calculations have been performed with one-dimensional hydrodynamic codes.

The results of numerical and theoretical studies of the gain of a direct-drive inertial confinement fusion target, which includes a kinetic description of energy transfer by laser-accelerated fast electrons, are presented. The range of the initial temperature of the fast electrons and the fraction of laser energy contained in these particles were chosen based on the results of recent experiments at the National Ignition Facility. The effect of 'wandering' of fast electrons is taken into account which is due to the remoteness of the region of fast electron generation from the ablation surface of the imploded target. As a result a significant fraction of particles do not fall into the compressed part of target. The 'wandering' effect leads to a decrease in the negative effect of fast electron generation on the gain of the target.

The paper is devoted to the numerical and theoretical study of compression and burning of a thermonuclear target under the conditions of inhomogeneous heating due to direct irradiation with a multi-beam megajoule laser facility. The two-dimensional distribution of absorbed laser energy has been numerically calculated taking into account refraction and various known factors of the violation of irradiation homogeneity. The limits of the violation of irradiation uniformity caused by these factors, which are acceptable for spark ignition of the target irradiated with 192 laser beams of the modern megajoule facilities, are determined. The target offset relative to the aiming point of the laser beams should not exceed 2% of the target radius, mispointing of the beams (5% of the target radius), mistiming of the laser pulses (3% of the pulse duration) and energy imbalance among the laser clusters (12%). These values exceed the permissible deviations for the laser facility being developed within the frameworks of the project.

We consider the physicomathematical model for the simulation of the angular laser flux distribution in a spherical target with the inclusion of radiation refraction in the corona. The irradiation uniformity is simulated using the target irradiation scheme on a megajoule multiple-beam laser facility. Calculations are made of the time-dependent angular distribution of absorbed flux and of the angular distribution of the time-integrated characteristic – the absorbed energy with allowance for the temporal shape of laser pulses – as well as of the time dependence of absorption efficiency. Different versions of target irradiation are considered. Under conventional irradiation it is assumed that the axes of all laser beams of equal energy pass through the target centre and the irradiation nonuniformity is due to its geometry only. Also examined are three unconventional irradiation versions: when there is a small spread of beam energies, when the target is displaced from the common beam pointing centre, and when the beam axes have small random deviations from the target centre. It is shown that the nonuniformity of the angular distribution of absorbed flux is greatest when the target is displaced from the beam pointing centre.

The heating of an inertial confinement fusion (ICF) target by fast electrons, which are generated as a result of laser interaction with the expanding plasma (corona) of a target, is investigated theoretically. It is shown that due to remoteness of the peripheral region, where electrons are accelerated, a significant portion of these particles, moving in corona and repeatedly crossing it due to reflection in a self-consistent electric field, will not hit into the compressed part of target. Using the modern models of fast electron generation, it is shown that in a typical target designed for spark ignition, the fraction of fast electrons that can pass their energy to the compressed part of the target is small. Only 12% of the total number of fast electrons can do it. Such an effect of 'wandering' of fast electrons in corona leads to a significant decrease in the negative effect of fast electrons on target compression. Taking into account the wandering effect, the distribution of energy transmitted by fast electrons to different parts of target and the resulting reduction of deuterium–tritium (DT) fuel compression are established.

Determination of the spectra and yields of thermonuclear particles is an actual research line for inertial confinement fusion (ICF) in two areas: the development of diagnostic methods for ICF plasma and thermonuclear reactor design for energy production. The latter is particularly important for thermonuclear neutron emission, which contains the bulk of the evolving energy. This work is devoted to the determination and analysis of the energy spectrum composition of the emissions of thermonuclear neutrons, charged thermonuclear particles and recoil nuclei from ICF targets, which correspond to a laser pulse energy of ≈2 MJ and are designed for modern experiments to achieve a positive energy yield. The spectra are determined on the basis of hydrodynamic numerical simulations of ICF target burnup, modeling the generation of thermonuclear particles and their interaction with the target by means of the Monte Carlo method. The spectrum characteristics are discussed with reference to the problems of corpuscular diagnostics and radiation damage to the materials of thermonuclear reactor units.

Processes of explosion and expansion of laser targets, experiments with which could clarify the reason for the observed asymmetric distribution of matter in a remnant cloud of some supernovae (e.g., the Cassiopeia A supernova), have been simulated. By analyzing criteria of hydrodynamic similarity of conditions characteristic of an astrophysical object and experiment, targets for absorbed laser energies in the range of 1–100 kJ have been proposed. This work continues a series of previous studies of supernovae and the possibility of simulating a number of processes observed at the explosion of supernovae such as the motion of a shock wave in matter, development of hydrodynamic instabilities at interfaces between shells with different densities, and largescale mixing of layers of the central region of a star with elements initially located at the periphery of the remnant cloud under laboratory conditions with high-power lasers. The studies are based on the numerical simulation of the explosion and explosion of targets using one- and two-dimensional hydrodynamic programs.