Charge Exchange Signatures in X-Ray Line Emission Accompanying Plasma-Wall Interaction

Abstract

Directional flows of well-collimated energetic ions produced at laser-burnt-through foils were used to investigate transient phenomena accompanying the plasma interaction with surfaces of solid targets (generally known as plasma-wall interaction, PWI). The plasma jet launched from the rear surface of the 0.8-um-thick Al foil irradiated at oblique laser incidence with an intensity of 3×1014 W/cm2 was incident on the quasi-massive C target. The plasma x-ray self-emission was analyzed by focusing survey and high-dispersion spectrometers. The time-integrated, spatially resolved narrow-band spectra recorded close to the C surface exhibit a dip structure in the red-wing profiles of the hydrogenic Al Lyγ line which was attributed to the charge exchange between two stationary Coulomb centers represented by the Al XIII and fully stripped C ions. This identification of the charge exchange signatures in x-ray line emission is supported by hydrodynamic simulations of environmental conditions in the near-wall plasma and by predictions of the dips positions following from complementary theoretical models. The agreement between the experiment and theory validates the first high precision x-ray spectroscopic identification of charge exchange phenomena accompanying the PWI.