Yu. A. Mikhailov

Investigation of anomalous generation of ω 0 and 2ω 0 harmonics of heating radiation in laser plasma corona by means of holographic gratings

The problems concerning the development of high f -number spectrographs with high spectral and spatial resolution using holographic reflecting gratings, for the study of processes of harmonic generation in laser plasmas are considered. The concave holographic gratings and spectrograph schemes used in the “Delfin-1” installation are described. The anomalous generation of ω 0 and 2ω 0 harmonics from the subcritical density plasma region has been observed experimentally. Possible interpretations of the observed effect are given.

The investigation of heating and compression of high-aspect ratio targets with ‘Delfin-1’

Experimental results on the compression of shell targets with aspect ratio A = 150–250 in the “Delfin-1” installation are reported. The absorbed laser energy was 0·3 to 0·5 kJ. The maximum compression was 3·5 × 10 3 , the velocity of target compression at the final stage was 2·6 × 10 7 cm/s, neutron yield was 10 6 to 10 7 D-D neutrons per laser shot. The appearence of plasma corona filamentation correlated with compression stability distruction.

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.”

Investigation of laser plasma dynamics using the X-ray spectra of multicharged ions☆

Abstract Results are reported on the study of the structure of optically thick laser plasmas from the intensity of X-ray spectral lines. The analysis of plasma images provides information about the average velocity of the plasma expansion, the hydrodynamic efficiency and the rate of the target evaporation.

Investigation of Plasma Parameters at the Spherical Heating of the Isolated Solid Target by High-Power Laser Radiation

The results of the investigation of high-temperature non-stationary plasma produced at the spherical heating of the ball-shaped (CD2)n target by high-power irradiation of the 9-channel laser setup are reported. It had been found that the fraction of absorbed energy reached 70% of the incident radiation at flux densities ~ 1014 – 1015 W cm−2. About 10–25% of the energy absorbed in the target is reemitted in the X-ray spectral range, while the fraction of energy reflected from plasma was not greater than 10%. The study of gas-dynamic parameters of the hot plasma “corona” made it possible to measure the pressure in the dense plasma core. The pressure was about 106 – 107 atm at the flux density of about 1015 W cm−2. Experimental data on measuring density, velocity and pressure in the “corona” region made it possible to conclude about experimental realization of the compression value of the order of 30.

Focusing crystal mirrors for X-ray diagnostics of laser-produced plasma

The paper describes an investigation of the characteristics of spherical focusing Bragg-reflection mirrors. The integral reflectivity of bent crystals at Bragg angles 80–90°, the width of the spectrum of the reflected x-rays, and the spatial resolution of the images formed by the focusing crystals are considered. Results are presented of the calculated integral reflectivity of bent silicon and quartz crystals of different orientation and in different orders of reflection. The feasibility is demonstrated of laser-plasma diagnostics using the images obtained with the aid of a multichannel x-ray microscope based on focusing crystals. Possible schemes of active diagnostics of a dense laser plasma using a monochromatic transilluminating x-ray beam are considered.

Measurement of the dynamics of the compression of high aspect-ratio shell targets in the “Delfin-1” installation

Abstract With the help of a specific diagnostic system designed for the “DELFIN-1” installation we have measured implosion velocities ≳ 250 km/s, which are record values for experiments on compression at sufficiently high hydrodynamic efficiency of ablative shell targets. An empirical scaling is shown to agree well with the measured compression velocities.

Powerful 12-Channel Laser Installation “Delfin” for Spherical Heating of Thermonuclear Targets

A 12-beam powerful laser installation “Delfin” for high-temperature spherical heating of thermonuclear targets is described. The installation consists of a Nd-Iaser (ultimate energy about 10kJ, pulse duration 1 ns and 0.1 ns, and divergence of 5 ×10-4 rad), target chamber for laser plasma interaction research, and a set of diagnostic systems to study laser and plasma parameters. The optical scheme and constructive peculiarities of the laser system are under consideration. Analysis of the focusing scheme is performed and a description of the focusing system of “DELFIN”, which makes it possible to obtain a high degree symmetry of spherical illumination of the target, is given. Expected flux density at the target is 1015 W/cm2, while the laser power is about 10 TW. The theoretical analysis of ultimate possibilities of concentration of the multi-beam laser radiation in the spherical target has been performed, when the really attainable radiation parameters have been taken into account. For a given target structure the ultimate energy, which can be focused in the target, seems to occur. The theoretical estimation has resulted in a successive-parallel scheme of the powerful laser, which is optimal. This scheme has been used in “DELFIN.”

Analysis and 2D numerical modeling of burn through of metallic foil experiments using power KrF and Nd lasers

The modeling of foil burn through effect with the help of traditional Lagrangian codes ( for example, “ATLANT”-code [4] has some difficulties. We are developing Euler 2D and 3D codes. It allows us to solve the problems of foil burn through, the input of a laser beam into a cavity [5] and other one. “NUT-CY”-code solves numerically the gas dynamic equations and electron heat conductivity in 2D cylindrical geometry ( r,z,t). It is assumed that the laser beam is propagating strictly along the axis ( 0Z ) and is absorbed due to bremsstrahlung mechanism. The laser flux which reaches the critical surface is absorbed in the cells. EOS is the ideal plasma.

Anomalous high energy electron emission from laser plasma

An original method based on direct measurements of electron emission has been proposed. The energy of fast electrons experimentally has been observed up to the value of 200 keV with current flux density 105 A/cm2. The dependencies of electron energy on radiation flux density as well as current density corresponding to cut off boundary of electron energy have been measured in the range of plasma temperatures from 70 to 200 eV. It is observed that a hydrodynamic instability leads to sharpening electron current pulse front at electron energy exceeding 100 eV. In the range of 1−10 keV the value of electron current more than 2 kA has been recorded. In this case, the current pulse duration is a few times more than the laser pulse, and the current pulse front is comparable with it.