Radiation of high-Z atoms sputtered by plasma

In this paper we apply a time-dependent radiative-collision model for analysis of radiation of impurity atoms sputtered in uniform plasma. As an example we consider spectroscopy data of neutral molybdenum atoms sputtered in argon plasma at PR-2 linear plasma device. We use effective collision strengths for electron impact excitation/de-excitation and spontaneous emission obtained earlier by relativistic R-matrix calculations. The ionization rates resolved by excited levels are estimated by the approximate ECIP method. The main feature of the experimental spectra is the maximum of radiation intensity situated at a noticeable distance from the target surface, different for different wavelength. This feature is reproduced by our calculations proving that appearance of the maximum is due to slow excitation of some levels. In contrast to the previous works on the problem, we demonstrate that neither electron-impact ionization nor escape of atoms from the plasma column are necessary for appearance of the maximum. We also show that if the initial population of atoms in excited state exceeds a certain limit, 5% in our particular case, the maximum disappears completely, giving the upper estimate of the initial population.