A. A. Rupasov

Compression of Laser-Irradiated Hollow Microspheres

Recent experiments with solid and shell targets proved the existence of high compression of the substance in the center of the target1–7, The ultimate compression and temperature are specified by the mechanisms of absorption and conversion of high-power laser radiation energy to the plasma energy, by the dynamics and stability of compression, and by the processes occurring in a plasma corona8–11.

Ablation loading of solid target through foam absorber on ABC laser at ENEA-Frascati

This work reports an experimental characterization of the efficiency of energy transmission of porous laser absorbers as a function of their density and thickness. In this campaign the foams were deposited on different metal substrates, which finally absorbed the energy deposited by the laser on the bulk of the porous material. The dimensions of the craters produced on the substrate can be related to the energy transmitted through the foams.

Thermal conductivity of laser-produced plasma corona

Various methods of theoretically describing the thermal conductivity of a of plasma corona are considered. The processes of laser heating and ablating a spherical-shell target in the “TRITON” program (Inst. of Appl. Mech., USSR Acad. Sci.) are computer-simulated. Numerical and analytic methods are used to investigate the influence of heat-transport suppression on the principal hydrodynamic characteristics of the plasma. It is shown that the most sensitive to a reduction of the heat transport is the electron-density distribution in space and in time. The requirements imposed on experimental measurements capable of determining, in comparison with numerical computations, the degree of heat-transport suppression, are analyzed for a large range of flux densities. It is shown that when the flux density is decreased to ≃1013 W/cm2 the present accuracy of measuring the position of the criticaldensity region in the corona, as well as the rate of evaporation of the material, becomes inadequate to determinethe deviation of the thermal conductivity from the classical value. Reliable conclusions concerning the transport coefficients can be drawn in this case from a comparison of high-speed interferometry data on the dynamics of a low-density corona (π/πcr = 10-3–10-1) with the results of computer simulation.

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.

Plasma formation dynamics for laser interaction with near critical foam matter

This work is devoted to an experimental investigation of dynamical processes taking place during the laser beam irradiation of the foam targets made from light elements under the conditions of the electron conductivity thermal wave formation.

Scattering of laser radiation at the heating of low density foam targets

Experimental study of the radiation scattered at the laser heating of low density foam targets is presented. The scattered radiation was investigated using spectrometers and streak cameras providing spatial, angular, spectral and temporal resolutions that enabled 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.