Velocity gradient induced line splitting in x-ray emission accompanying plasma-wall interaction

•Impact of energetic plasma jets on solid targets is studied by x-ray spectroscopy.•Velocity gradients of ions in near-wall plasma were measured and modeled.•Doppler effect induced line splitting was attributed to ion backscattering.•Scenario of plasma-wall interaction was derived from theoretical modeling.

High-resolution x-ray spectroscopy was applied to study the ion back-scattering in plasma-wall interaction. In experiments carried out on the Prague Asterix Laser System (PALS), the energetic ions produced at thin laser burnt-through Al foil impacted the secondary C target where they were decelerated, trapped and scattered in radial and backward directions. The environmental conditions in near-wall plasmas were analyzed using the high-dispersion x-ray spectroscopy and temporally-resolved x-ray imaging. The radial expansion of ions back-scattered in the near-wall region was directly observed via the Doppler effect induced splitting of the Al Heα intercombination line. The experimentally observed line splitting was modeled using a combination of the 2D arbitrary Lagrangian Eulerian hydrodynamics code PALE with the multifluid code MULTIF and spectrally postprocessed using HULLAC atomic model builder and CRETIN collisional-radiative code.