Modeling of high-pressure rare gas plasmas excited by an energetic flash X-ray source

In this paper, a comprehensive description of the kinetics of argon plasmas has been formulated for atmospheric pressures. It has been used to attribute to molecular species the ultraviolet-vacuum ultraviolet (UV-VUV) continua, observed between 150 and 300 nm in pure argon. The participation of both ionic dimers and trimers has been found to be necessary to explain the whole fluorescence emitted by the rare gases (Rg). A simple kinetic model of high-pressure (1-30 bar) argon plasmas created by flash X-ray excitation is reported. The photoexcitation of Rg at high pressure by X-ray photons with energy of about 10 keV is shown to produce plasmas with significant density gradients of ionic and excited species. Spatial analysis of the energy position along the X-ray penetration path is performed in order to account for these concentration gradients. The calculation of electron density in different Rg (Ar, Kr, Xe) excited by X-ray photons of various energies (0.2-10 keV) is also reported. From these results, it appears that hash X-ray excitation of Rg can be a very interesting means to produce high-electron-density plasmas designed to selectively emit intense fluorescence in the UV-VUV spectral domain.