RESUMO
We present results for Stark broadening of high principal quantum number (up to n=15 ) Balmer lines, using an analytical (the "standard theory") approach and two independently developed computer simulation methods. The line shapes are calculated for several sets of plasma parameters, applicable to radio-frequency discharge (N(e) approximately 10(13) cm(-3)) and magnetic fusion (N(e) approximately 10(15) cm(-3)) experiments. Comparisons of the calculated line profiles to the experimental data show a very good agreement. Density and temperature dependences of the linewidths, as well as relative contributions of different Stark-broadening mechanisms, are analyzed. It is seen that the standard theory of line broadening is sufficiently accurate for the entire set of plasma conditions and spectral transitions considered here, while an alternative theory ("advanced generalized theory") is shown to be inadequate for the higher-density region. A discussion of possible reasons for this disagreement is given.
RESUMO
A reported anomaly in the experimental scaling of the widths of Stark broadened n=3, Delta n=0 spectral lines along the carbon isoelectronic sequence is not observed in the present experiments. The ratio omega(N)/omega(O) of widths for N II lines compared to those for the narrower O III lines for the same transitions is now measured as lying between two theoretical predictions, both of which show a value omega(z-1)/omega(z) greater than unity continuing throughout the sequence. In the earlier measurements, the widths (in frequency units) were actually measured as being smaller for N II than for O III, i.e., a ratio omega(z-1)/omega(z) less than unity.
RESUMO
Order-of-magnitude anomalously high intensities for two-electron (dielectronic) satellite transitions, originating from the He-like 2s(2) 1S0 and Li-like 1s2s(2) (2)S(1/2) autoionizing states of silicon, have been observed in dense laser-produced plasmas at different laboratories. Spatially resolved, high-resolution spectra and plasma images show that these effects are correlated with an intense emission of the He-like 1s3p 1P-1s(2) 1S lines, as well as the K(alpha) lines. A time-dependent, collisional-radiative model, allowing for non-Maxwellian electron-energy distributions, has been developed for the determination of the relevant nonequilibrium level populations of the silicon ions, and a detailed analysis of the experimental data has been carried out. Taking into account electron density and temperature variations, plasma optical-depth effects, and hot-electron distributions, the spectral simulations are found to be not in agreement with the observations. We propose that highly stripped target ions (e.g., bare nuclei or H-like 1s ground-state ions) are transported into the dense, cold plasma (predominantly consisting of L- and M-shell ions) near the target surface and undergo single- and double-electron charge-transfer processes. The spectral simulations indicate that, in dense and optically thick plasmas, these charge-transfer processes may lead to an enhancement of the intensities of the two-electron transitions by up to a factor of 10 relative to those of the other emission lines, in agreement with the spectral observations.
RESUMO
Possible inconsistencies between the recent hydrogen H(alpha) spectral line shift measurements and modifications of the theory of these shifts by Escarguel et al. [Phys. Rev. E 62, 2667 (2000)], and earlier measurements in dense plasmas and corresponding calculations are discussed. Some of the claimed differences may likely be due to underestimates of Debye shielding effects and to differences between definitions of line shifts in the case of asymmetric profiles.
