Diagnosing selenium plasmas using Se XXVI and Se XXXV line cluster ratios

Ratios of resonance and satellite line clusters in fluorinelike (Se XXVI) and neonlike (Se XXV) ions are used in the development of a diagnostics procedure for analyzing high density, optically thin selenium plasmas. The atomic model employed in this work to calculate line intensities for n=2-3 transitions includes detailed fine-structure levels for the n=3 excited configurations, n=3 inner-shell excited states at the configuration level, and lumped n=4 levels for both Se XXVI and Se XXV. All relevant atomic processes connecting these levels and all collisional couplings among the excited states are included in the model. The collisional and radiative data such as collisional excitation and ionization (including inner shell), and both radiative and dielectronic recombination rates, are obtained using several different sophisticated atomic codes. From these data, collisional-radiative equilibrium solutions to a fully coupled single set of rate equations are obtained for the populations of the ground as well as all excited levels, and used for the computation of the line intensities. For calculations of the satellite line intensities, populations of the doubly excited states are obtained from the sum of contributions from dielectronic recombination of ground states and inner-shell excitation of singly excited states. Because experimental L-shell spectra of the n=2-3 resonance and satellite lines contain many lines, often they are not spectroscopically resolved unless obtained under extremely high resolution. Therefore, instead of using individual lines which often cannot be separated experimentally from other overlapping lines, resonance line as well as satellite line configuration clusters in Se XXVI and Se XXV are used in this diagnostic work. The intensity ratios of the resonance and satellite line clusters are functions of both electron temperature and ion density and simultaneous determinations of these quantities are possible using contour plots of specific cluster ratios. These plots are obtained for a wide range of densities and temperatures, and they reflect the detailed effects of the different atomic processes on the intensities of the resonance and satellite lines as a function of plasma conditions.