I. G. Lebo

2D numerical simulation of the interaction of high-power laser pulses with plane targets using the “ATLANT-C” Lagrangian code

The “ATLANT-C” program developed for the two-dimensional (2D) simulation of problems of Lagrangian gas dynamics is described. The difference scheme of gas dynamics with an increased number of thermodynamic degrees of freedom used in the program preserves the plane, cylindrical, and spherical symmetry of the one-dimensional (1D) flows. The approach proposed provides an improved retention of the shape of the computational cell and the solution of problems incomputable with the conventional schemes. The efficiency of the algorithms applied is confirmed by the test calculations and results of simulation of actual physical experiments.

Efficiency of laser energy input into a hohlraum through a hole

Results are presented from the two-dimensional numerical simulations of laser energy input into a hohlraum through a hole. This problem is of interest for ICF research, specifically, for optimization of laser microtarget design. The optimum relations are found between the hole size and the effective laser spot radius under conditions close to those of present-day ICF experiments.

On the Influence of “Speckles” of Laser Radiation on Plasma Parameters when Irradiating Aluminum Foils by a Picosecond Pulse

The influence of the inhomogeneity of target heating on the plasma behavior when irradiating a target by a superhigh‐power short laser pulse (with intensity above 1016 W/cm2 and duration of about 10-12 s) was studied on the basis of two‐dimensional numerical calculations. In the presence of the speckle‐like structures in the laser‐radiation flux, the plasma parameters and, in particular, the temperature were shown to be essentially different from estimates based on the mean intensity within the focusing spot.

On the Neutron Yield in the Two-Beam Scheme of Laser Heating and Compression of Spherical Shell Targets with a Low‐Density Coating

At the initial stage of development of large-scale multiple-beam laser facilities for the “ignition” of the fusion reaction, facilities with a small number of beams is expected to be created. Such facilities are characterized by poor symmetry of irradiation of spherical targets. We have shown that with appropriate design of the target and distribution of the radiation intensity in laser beams the attainment of a neutron yield of 1015-1016 is possible even in two‐side irradiation of the spherical targets.

Physical processes in a laser-greenhouse target: Experimental results, theoretical models, and numerical calculations

The paper is devoted to recent results concerning investigation of physical processes occurring in a “laser greenhouse” target. Results of experimental and theoretical studies of laser-pulse interaction with a low-density absorber of the target, namely, with a porous substance having density close to the plasma critical density, are presented. On the basis of a vast cycle of experiments carried out in a number of laboratories, it is shown that the absorption of the laser radiation in porous media, including those with a density exceeding the critical one by at least a factor of 4 to 6, has a bulk nature and is distributed over the target depth. In particular, the laser-radiation absorption region in a porous substance with density 10−3–10−2 g/cm3 is extended into the target 400–100 μm, respectively. The coefficient of absorption of laser radiation with intensity 1014–1015 W/cm2 in porous substances, including those of the supercritical density, is 70–90%. Experiments have not shown enhanced (compared to a solid-state target) radiation intensity associated with a possible development of parametric instabilities in an extended laser plasma of low-density porous media, as well as noticeable contribution of fast electrons to the energy balance and their effect on the energy transfer. In this paper, theoretical models are developed explaining features of the laser-radiation absorption and energy transfer in porous media. These models are based on the phenomenon of laser-radiation interaction with solid components of a porous substance and plasma production inside pores and cells of the medium. The efficiency of energy conversion in the vicinity of the ignition threshold for the laser-greenhouse target is investigated in the case of an absorber having the above properties. Numerical calculations have shown that a thermonuclear-gain coefficient of 1 to 2 (with respect to the energy absorbed) is attained for a laser-radiation energy of 100 kJ.

A model for development of Rayleigh-Taylor instability in a shell of an incompressible fluid in the presence of ablation

In this study, a model for development of Rayleigh-Taylor instability at the surface of a spherical shell of an incompressible fluid under the condition of ablation compression by laser radiation is discussed. The closedness of the model is attained by means of the quasi-steady laser-corona approximation. The stabilizing role of evaporation, which was emphasized many times previously, is also confirmed in the case under consideration. However, numerical calculation testifies to the qualitative and quantitative difference in the behavior of perturbations in the general case compared to predictions of the well-known Bodner-Takabe formula. In our opinion, this fact is associated with the essentially unsteady nature of the compression process.

Numerical Simulation of Evolution of Multimode Initial Perturbations in the Development of Richtmyer-Meshkov Instabilities

Results of two-dimensional and three-dimensional numerical calculations simulating development of multimode initial perturbations of the contact interface between two gases when shock waves pass through it are presented. A method of solving gas-dynamic nonlinear equations is described. The calculations are performed using an HP-712 workstation and a PARSYTEC CC multiprocessing computer system based on 12 processors.