Numerical Simulation of the Absorption of Laser Radiation in a Plasma Including the Resonance Mechanism and Generation of Fast Electrons for the Conditions of a Nuclear Fusion Target Ignition

Abstract

A model of resonance absorption of laser radiation in a plasma involving the deformation of the density profile by the ponderomotive force has been proposed. A mechanism of the linear transformation of laser radiation into plasma waves at resonance absorption has been discussed. The quasilinear diffusion equation for the electron distribution function in the plasma field has been used to describe the generation of fast electrons by plasma waves. Formulas have been obtained to estimate the energy fraction absorbed through the resonance mechanism and the energy of fast electrons. These formulas have been used in the two-dimensional hydrodynamic code ATLANT-HE. The hydrodynamics of the plasma and the absorption of laser radiation have been calculated for conditions of the NIF facility experiment at a radiation power of 30 ТW and a base pulse duration of 7.5 ns. The plasma has the spatial dimensions appearing upon the irradiation of a spherical target for the initiation of the fusion reaction. The calculations have shown that the resonance absorption mechanism leads to the generation of fast electrons with an energy of about 40–80 keV. Fast electrons carry an energy of about 1–1.5% of the laser energy. These results are close to the experimental data.