Formation of a plane layer of plasma under irradiation by a soft X-ray source

Abstract

We investigate theoretically the formation of a plasma in a plane layer of polymer foam (density ρ = 0.002 g/cm3 and thickness 800 μm) under the action of an external source of soft X-ray radiation under the conditions of PHELIX experiments. The incident flux is assumed to have a Planck’s distribution over the spectrum with Trad = 20–40 eV. In numerical calculations, the flux of incident X-ray radiation and the spectral constants of the target substance are varied. The action of an external X-ray radiation source on a low-density foam substance with a density of 2 mg/cm3 causes a plasma to be formed with relatively homogeneous profiles of density and temperature T = 15–35 eV. Absorption of externalradiation energy is distributed in the volume. The plasma temperature increases with increase in the external energy, and the energy passed through the plasma also increases. The results prove to be sensitive to the values of optical constants used in numeral simulation. The spectral flux of external radiation passed through the plasma is chosen as a criterion of correctness of the optical constants used in the calculations. In future experiments using the PHELIX facility, we plan to investigate the slowing-down of an ion beam in a plasma formed as a result of indirect heating of low-density polymer triacetate cellulose (TAC) foam with densities ρ = 0.001–0.01 g/cm3 under the action of a pulse of X-ray radiation, into which the laser radiation is preliminarily transformed.