Laser plasma generation and plasma interaction with ablative target

Abstract

The model of plasma production by laser radiation onto a solid target was developed taking into account plasma heating by the emitted electrons and target heating by ion bombardment, as well as by the laser radiation. The near target plasma structure was analyzed. The space charge sheath was studied solving the Poisson equation and taking into account the volume charge of accelerated electrons and ions. The kinetics of atoms evaporated from the target and the back-flow of atoms and ions from the plasma towards the surface was analyzed. A system of equations, including equations for solid heat conduction, plasma generation and the plasma expansion was formulated. The calculation for Cu target, laser spot radius 100 μm, pulse duration 1 ms, 103, 10, 1ns and laser power density qL = 10−3–1 GW/cm2 was conducted. The ratio of net evaporation rate to the total evaporated mass flux was determined. It was shown that the plasma mainly generated in the electron emission beam relaxation region and there the plasma flow is subsonic. The electric field at the target surface is relatively large and therefore the ion current to the surface in the space region is large and comparable with the electron emission current. A large contribution of the plasma energy flux in the target heat regime was obtained, showing that the laser generated plasma significantly converts the absorbed laser energy to kinetic and potential energy of the plasma particles, which transport part of the energy through the electrostatic sheath to the solid surface.