Shift and broadening of isolated neutral helium lines 7281Å (2 1 P − 3 1 S), 7065Å (2 3 P − 3 3 S), 6678Å (2 1 P − 3 1 D), 5048Å (2 1 P − 4 1 S), 4922Å (2 1 P − 4 1 D) and 4713Å (2 3 P − 4 3 S) in a dense plasma are investigated. Based on a quantum statistical theory the electronic contributions to the shift and width are considered, using the method of thermodynamic Green functions. Dynamic screening of the electron-atom interaction is included. Compared to the width, the electronic shift is more affected by dynamical screening. This effect is increasing at high density. A cut-off procedure for strong collisions is used. The contribution of the ions is taken into account in a quasi-static approximation, with both the quadratic Stark effect and the quadrupole interaction included. The results for shift and width agree well with the available experimental and theoretical data.
The interpretation of hydrogen Balmer spectra emitted from a high-pressure arc discharge (Radtke and Günther, Contrib. Plasma Phys. 26, 143 (1986)) is re-examined. Assuming local thermodynamic equilibrium, synthetic Balmer spectra are calculated for given temperature and density conditions. Radiation transport is accounted for using a one-dimensional plasma layer model. The lineshape of bound-bound transitions is determined using a microscopic quantum-statistical approach. Free-free and free-bound contributions are added by taking expressions from literature. Comparing the synthetic spectra with experimental ones, plasma temperature and density conditions are inferred. The plasma parameters are confronted with theoretical results for the compositions of dense plasma.
To apply spectroscopy as a diagnostic tool for dense plasmas, a theoretical approach to pressure broadening is indispensable. Here, a quantum-statistical theory is used to calculate spectral line shapes of few-electron atoms. Ionic perturbers are treated quasistatically as well as dynamically via a frequency fluctuation model. Electronic perturbers are treated in the impact approximation. Strong electron-emitter collisions are consistently taken into account with an effective two-particle T-matrix approach. Convergent close-coupling calculations give scattering amplitudes including Debye screening for neutral emitters. For charged emitters, the effect of plasma screening is estimated. The electron densities considered reach up to n(e) = 10(27) m(-3). Temperatures are between T = 10(4) and 10(5) K. The results are compared with a dynamically screened Born approximation for Lyman lines of H and H-like Li as well as for the He 3889 Å line. For the last, a comprehensive comparison to simulations and experiments is given. For the H Lyman-α line, the width and shift are drastically reduced by the Debye screening. In the T-matrix approach, the line shape is notably changed due to the dependence on the magnetic quantum number of the emitter, whereas the difference between spin-scattering channels is negligible.
We re-examine several Balmer spectra obtained from high-pressure arc discharges (Radtke and Günther, Contrib. Plasma Phys. 26, 143 (1986); Radtke, Günther, and Spanke, ibid. 26, 151 (1986)). By matching synthetic spectra to the experimental line profiles, we infer plasma parameters such as density, temperature, and composition. Spectral line modeling is based on a microscopic quantum statistical approach. Corrections accounting to the merging lines near the threshold are describe following a model of D'yachkov. Self-absorption is clearly visible in the spectra and accounted for in one-dimensional model assuming thermal equilibrium. A consistency check is performed by comparing to the broadening of silicon impurity lines, where present in some of the spectra. Furthermore, a comparison is made with predictions from a fluid variational model for the composition and the equation of state of the plasma.
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