The turbulent mixing (TM) of different DT-fuel areas (cold with hot) and of DT-fuel with ablator is one of the deciding factors, determining the neutron yield from compressing laser fusion, and, more generally, inertial confinement fusion (ICF) targets. A lower than predicted neutron yield gained in experiments is not studied comprehensively, but can be caused by the mixing processes. A study of mixing in the ICF problem is complicated by density gradients, spherical convergence, compression, etc., so we suppose the fundamental understanding of the mixing processes must be acquired first in the problem of classical Rayleigh-Taylor (RT) instability in plain geometry. In our work we present results, obtained by the supercomputer numerical modeling of RT-induced TM processes with different initial conditions in 2D and 3D geometries conditions on a high-resolution meshes. For analysis of the modeling results we use an evolutionary model of singular perturbation development, including linear and non-linear stages. This theoretical approach allows us to obtain highly detailed view of the mixing zone evolution along with possibility to trace the initial conditions influence on the mixing late stages.

We investigate the efficiency of inertial fusion target compression, where at the initial time moment the thermonuclear fuel is in a two-phase state and has the form of two adjacent layers — the external DT-liquid layer and the internal DT-ice layer. We study this problem for the fast ignition targets, where the ultimate final density of the thermonuclear matter is of a special importance. We take the simplest type of a fast ignition target, which corresponds to the technical justification of the HiPER Project aimed at demonstrating fast ignition at the compressing laser pulse energy ~100 kJ. Such a target presents a spherical DT-ice shell coated with a thin polymer film. We obtain the dependence of the final target density on the mass fraction of the DT-matter liquid phase and formulate the requirements on the admissible concentration of liquid phase if the decrease in the DT-fuel final density does not exceed 10%. We find the criterion for choosing the laser-pulse duration which provides the minimum decrease in the final density of the target containing DT-matter in the initial two-phase state.

The problem is to find particular schemes for different tasks. The competing processes under the laser plasma heating are the plasma thermal radiation and the plasma expansion, i.e. the conversion of the laser pulse energy into the plasma kinetic energy. The efficiency of the two mentioned processes depends on the density and size of plasma, and may be effectively controlled by the two parameters, that is, a decrease in density and an increase in the target size, which enhance the efficiency of radiation. The radiation spectrum depends on the plasma composition and a concentration of heavy-ion admixtures in the plasma. During the last two years, the laser fusion scientists were engaged in studying the processes of energy transformation and transfer (including the radiation) in low-density structured foam-like media with an admixture of heavy elements.It was experimentally found that under laser irradiation of a foam-line target with a heavy ion admixture it is possible to produce the radiation with the efficiency close to 50%.The present report concerns a theoretical basis and the experimental results related to the problem.

We investigate theoretically the formation of a plasma in a plane layer of polymer foam (density ρ = 0.002 g/cm3 and thickness 800 μm) under the action of an external source of soft X-ray radiation under the conditions of PHELIX experiments. The incident flux is assumed to have a Planck’s distribution over the spectrum with T rad = 20–40 eV. In numerical calculations, the flux of incident X-ray radiation and the spectral constants of the target substance are varied. The action of an external X-ray radiation source on a low-density foam substance with a density of 2 mg/cm3 causes a plasma to be formed with relatively homogeneous profiles of density and temperature T = 15–35 eV. Absorption of externalradiation energy is distributed in the volume. The plasma temperature increases with increase in the external energy, and the energy passed through the plasma also increases. The results prove to be sensitive to the values of optical constants used in numeral simulation. The spectral flux of external radiation passed through the plasma is chosen as a criterion of correctness of the optical constants used in the calculations. In future experiments using the PHELIX facility, we plan to investigate the slowing-down of an ion beam in a plasma formed as a result of indirect heating of low-density polymer triacetate cellulose (TAC) foam with densities ρ = 0.001–0.01 g/cm3 under the action of a pulse of X-ray radiation, into which the laser radiation is preliminarily transformed.

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.

The present report presents an analytical model destined to describe the development of hydrodynamic instabilities and their influence on the neutron yield under laser target compression. A number of specific numerical simulations formed the basis of the analysis. The plane and spherical tasks with certain initial conditions were considered. In a plane case the two pairs of gases typical for the shock tube experiments were studied. The spherical task was the modeling one and involved a small number of harmonics ( the calculation parameters corresponded to the regime of laser compression). A notable difference in the calculation parameters of the gases in shock tubes and the laser compressed targets is not an obstacle for the construction of a unified model, since in gas dynamic problems the fundamental properties of gas-dynamic similarity are fulfilled.Basing on the simulations [1] and theory [2], the authors constructed a model of mixing zone development, which takes into account the initial conditions of perturbation. In addition to the earlier studied problems the report presents 2D-simulations of spherical target compression with account for the mixing processes. The simulations were aimed at determination of the degree of the mixing zone influence on the neutron yield.

A low-density plastic aerogel foams, including doped with copper clusters have been irradiated by the first (L = 1.315 Fm) and third (L = 0.438 Fm) harmonics of the PALS iodine laser. Laser pulse duration was approximately 380 ps (FWHM), laser energy was up to 300 J, and laser intensity on the target was typically by an order of 1014−1015 W/cm2. The targets were of a fine-grain structure with the pore size in the range of 1-2 Fm. The energy transfer in plasma was measured by the X-ray and optical diagnostics. The observed phenomena are explained via mathematical modelling of the processes in plasma performed by fluid codes RAPID and LATRANT, developed at P.N. Lebedev Physical Institute and the Institute of Mathematical Modelling of RAS, Moscow. Our simulations take into account a microscopic structure of porous matter and energy transfer and loss by the X-ray emission. The plasma radiative characteristics were calculated by DESNA code. The analysis of the experimental and calculated data allows one to find the energy balance in the target and the plasma characteristics important for the dynamics of the processes.

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 = R 0 /ΔR 0 , the conversion ratio R 0 /R min , and the lesser value α = p/p F . 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.

Experimental and theoretical results of investigations of the iodine laser - Al solid target interactions on the PALS (Prague Asterix Laser System) facility are presented. The experimental investigations of laser interaction with massive Al targets devoted to shock wave propagation in solids and crater formation physics are presented. Experiments were performed with the use of high intensity laser pulses (10(13-15) W/cm(2)) for two laser wavelengths (0.438 mum and 1.315 mum) and four laser beam radii (from 35 mum up to 600 mum). The crater dimensions were measured using optical microscopy and a wax-replica technique. Plasma expansion out of the target was measured via three-frame interferometry. Theoretical model of the post-pulse crater formation by the shock wave propagating and decaying in solids after the end of the laser pulse is presented and applied for the explanation of the results obtained in experiments.