S. I. Fedotov

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.

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.

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.”

System for nanosecond and picosecond laser synchronization using high-voltage semiconductor switches

Results are presented on the development and investigation of a system for the synchronization of the emission of a nanosecond laser, used for plasma heating, with the emission of a diagnostic picosecond laser. The system is based on the use of the fast-semiconductor-switch technology, and ensures a temporal synchronization instability not higher than 100 psec.