Vladislav B. Rozanov

Theoretical and experimental studies of the radiative properties of hot dense matter for optimizing soft X-ray sources

Theoretical and experimental studies of radiative properties of hot dense plasmas that are used as soft X-ray sources have been carried out depending on the plasma composition. Important features of the theoretical model, which can be used for complex materials, are discussed. An optimizing procedure that can determine an effective complex material to produce optically thick plasma by laser interaction with a thick solid target is applied. The efficiency of the resulting material is compared with the efficiency of other composite materials that have previously been evaluated theoretically. It is shown that the optimizing procedure does, in practice, find higher radiation efficiency materials than have been found by previous authors. Similar theoretical research is performed for the optically thin plasma produced from exploding wires. Theoretical estimations of radiative efficiency are compared with experimental data that are obtained from measurements of X-pinch radiation energy yield using two exploding wire materials, NiCr and Alloy 188. It is shown that theoretical calculations agree well with the experimental data.

Nonequilibrium laser-produced plasma of volume-structured media and ICF applications

This paper is devoted to the investigation of powerful laser pulse interaction with regularly and statistically volume-structured media with near critical average density and properties of laser-produced plasma of such a media. The results of the latest experiments on laser pulse interaction with plane foam targets performed on Nd-laser facilities ABC in the ENEA-EURATOM Association (Frascati, Italy) and MISHEN in the Troitsk Institute of Innovation Thermonuclear Investigations (TRINITI, Troitsk Russia), and J-laser ISKRA-4 in the Russian Federal Nuclear Center, All-Russian Scientific Research Institute of Experimental Physics (RFNC-VNIIEF, Sarov, Russia) are presented and analyzed. High efficiency of the internal volume absorption of laser radiation in the foams of supercritical density was observed, and the dynamics of absorbing region formation and velocity of energy transfer process versus the parameters of porous matter are found. Some inertial confinement fusion (ICF) applications based on nonequilibrium properties of laser-produced plasma of a foam and regularly structured media such as the powerful neutron source with yield of 10 9 -10 11 DT-neutrons per 1 J of laser energy, laser-produced X-ray generation in high temperature supercritical plasma, and the compact ICF target absorbers providing effective smoothing and ablation are proposed.

Interaction experiments of laser light with low density supercritical foams at the AEEF ABC facility

Experiments have been performed on the interaction physics of laser light with polystyrene and agar-agar foams having average densities higher than critical. The experiments have been performed at the ABC facility of the Associazione EURATOM-ENEA sulla Fusione, in Frascati. The main addressed topics have been energy coupling (balance), diffusion of energy into the target, plasma and dense phase dynamics, and harmonics generation. The laser light (A = 1.054 μm) was focused by a F/1 lens to produce on the target surface about 1.6 X 10 14 W/cm 2 (10 15 W/cm 2 in the waist, set about 100 μm inside the target). Experiments have shown efficient energy coupling (>80%) to be attributed to cavity formation in the low density foam (efficient light absorption) and good mechanical coupling of the plasma trapped in the cavity to the dense phase (ablation pressure work). Heat diffusion possibly plays a transitory role in the initial stages of the interaction (300-500 ps). Time integrated harmonics measurements revealed a blue-shifted 2ω and a red-shifted 5/2ω.

Monte–Carlo simulations of fusion kinetic processes used to evaluate diagnostic techniques for laser target plasma

Review and systematization of our investigations in thermonuclear (TN) plasma particle diagnostic methods are presented. The proposed diagnostic schemes are based on direct numerical simulations of nuclear reaction products kinetics in a dense hot plasma with the following interpretation of the results by means of analytical scaling relations for charged particles energy loss in plasma with arbitrary degeneration of electron gas. The simulations of the kinetic equations system solution for TN particles is carried out by TERA code based on Monte-Carlo method. The diagnostic schemes are presented in the form of families of isoline curves at the (pR,T)-plane which are related to the constant values of measured spectrum characteristics. The searching plasma parameters pR and temperature T are determined by points of interceptions of curves related to the distinct characteristics. The ranges of applicability of different methods of particle diagnostics are investigated in detail.

Laser-produced post-pulse crater formation in solids observed in PALS facility interaction experiment

Results from PALS facility laser-massive Al target interaction experiments are reported. Main attention is devoted craters formation under the action of laser pulses of various energy (from 100 J up to 600 J), intensity (from 1013 W/cm2 up to 1015 W/cm2), laser wavelength (0.438 μm and 1.315 μm), and focal beam radius (from 35 μm up to 600 μm). Crater replicas were made of wax and their depths and radii were subsequently obtained by microscopy measurements. Duration of the laser-pulse-initiated shock wave propagation into the targets was much longer than that of the laser pulse itself (400 ps). This was an important feature of the experimental arrangement. 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 explanation of the results obtained in experiments.

Laser-generated weak shock wave propagation dynamics in the solids

The processes of the weak shock wave generation and propagation in the solid targets are studied by analytical and numerical methods. The impact of the laser pulse with wavelength (lambda) equals 1.06 micrometers and the pulse intensity I equals 1010-1012W/cm2 was considered as a wave source. The resulting wave with pressure about 1-100kBar is studied in a solid medium 0.5-1 mm thick. The results of modeling compared with experimental data shows correctness of hydrodynamical approximations for a given problem.

Calculation of optical characteristics of nonequilibrium plasma

A collisional-radiative model has bene developed to calculate the physical and optical characteristics of thermodynamical nonequilibrium plasma. The mean charge of plasma ions, the ionization-state density, radiative energy losses, line ratios, the opacities and the emissivities have been calculated for the steady-state optically transparent plasma, which contains aluminum or copper multi charged ions, in a broad range of plasma densities and temperatures. The comparison shows that our result agree satisfactorily with the calculation results of other authors and with the experimental data.

Anomalous burning through of thin foils at high brightness laser radiation heating

The results of the experiments at the installation “PICO,” with thin foils heating by laser radiation pulses of nanosecond duration are reported. The Al foils with thickness in the range from 3 μ up to 40 μ were used as targets. The flux density was varied from 10 13 W/cm 2 to 10 14 W/cm 2 . The sharp dependence of the portion of laser energy that passed through the target on foil thickness was observed. This phenomena was accompanied by a relatively small decrease of the passed radiation pulse duration. The anomalously high speed burning through of thin foil was observed in these experiments and the conclusion on the possible mechanism of this phenomena has been done on the base of comparison of experimental data with theoretical calculations. The observed phenomena can be interpreted with a conjecture about the local burning through of a target, in the small areas of the target surface, with many more values of flux density than the average one following laser radiation self-focusing and formation of “hot spots.”

Simulation of hydrodynamic phenomena caused by pre-pulse in picosecond laser-plasma interaction

We consider a physical model of the interaction of high-power laser pulses with plasma created upon irradiation of condensed targets. The model is based on the equations of single-fluid, two-temperature hydrodynamics taking into account the ponderomotive force and the Maxwell equations for laser radiation at oblique incidence in the cases of s- and p-polarizations. The model takes into account the generation of fast electrons in the conditions of plasma resonance at the critical surface, and their transport with consideration for the friction force, caused by the ionization losses. For a number of experiments we have performed the numerical modeling of the laser picosecond pulse interaction with targets. We present the interpretation of the experiment on the basic harmonic shift depending on the pre-pulse energy. It has been shown that, if under the irradiation of a deuterated target the pre-pulse energy grows, the neutron yield of DD-reactions diminishes, since the produced plasma prevents the heating of the dense part of the target. It has been also shown that the growth of the pre-pulse energy can provoke, due to the induced scattering, the losses in the main pulse radiation. We give interpretation of the experimental data on the picosecond pulse absorption by plasma at the flux density of 1016-1019 W/cm2.

Mean opacities of LTE plasmas: detailed configuration accounting versus other approaches

The hydrodynamic-radiation codes are used for a simulation of mean Rosseland and Planck opacities from different models similar to Hartree-Fock model, average ion model, detailed configuration accounting model, and so on. At present the necessity in such a data is high especially for plasma of mixture of ions. In this work we present the results on a comparison of mean opacities calculated by means of various codes and models. The calculations were carried out for the local thermodynamic equilibrium (LTE) plasmas of various chemical elements and mixtures. The models under consideration are the DESNA model and the THERMOS, JIMENA (analytical opacity formula), and the LEDCOP codes. The main results and conclusions about applicability of each of the approaches based on the comparison are presented for LTE plasma on Be, C, Al, SiO2. After verification, the results of the DESNA model calculations will be used to create the database on mean opacities in a broad range of plasma density and temperature for various materials, including the case of non-LTE plasma.