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Population inversions between the 3p and 3s levels of neonlike ions with atomic numbers Z=14, 18, 22, 26, 32, and 36 have been calculated. The population inversions result from the preferential population of the 3p level by electron collisional excitation from the ground configuration of the ion and occur over a wide range of electron temperature and electron density (from 1017 cm−3 for Si V to 1022 cm−3 for Kr XXVII). For all ions that are studied, the maximum value of the population inversion (N3p/g3p−N3s/g3s) for the transition 3p 1S0−3s uP1 (where u represents the upper of the singlet and triplet levels) is found to be approximately equal to 4×10−3 NI, where NI is the total density of neonlike ions. With the exception of Si V, laser gains greater than 1 cm−1 are possible for all the ions that are considered, and the gain increases with atomic number Z. For Si V and lower-Z ions, electron collisional mixing of the upper and lower laser levels restricts the electron density at which the population inversion occurs and limits the laser gain to values less than 1 cm−1. The scaling of the laser gain and the plasma parameters with atomic number Z is presented. For an electron density of 1021 cm−3, the optimum atomic number Z that results in the highest gain on the 3p 1S0−3s uP1 transition is Z=26 (Fe XVII), and the gain is equal to 30 cm−1.

Theoretical predictions are presented for the iron Ea x-ray emission spectra from hightemperature plasmas, assuming steady-state optically thin excitation conditions. Account has been taken of all fine-structure components of the 2p~1 s inner-shell-electron radiative transitions in the iron ions from Fe xvIII to Fe xxrv. The Ka emission spectra are assumed to be produced by means of dielectronic recombination and inner-shell-electron collisional excitation processes that involve intermediate autoionizing states belonging to electronic configurations of the type 1s'2s'2p'. In addition to the electron-temperature variation, which is attributable to the temperature dependences of the radiationless electron capture and inner-shell-electron collisional excitation rate coefficients and to the temperature dependence of the charge-state distribution, the Ka emission spectra exhibit an electron-density sensitivity. This electron-density sensitivity is a result of the density-dependent distribution of populations among the different fine-structure levels of the initial ions in the dielectronic recombination and inner-shell electron collisional excitation processes. In order to introduce a simplified treatment for the initial distribution of populations, whose precise determination would involve the detailed and self-consistent description of a multitude of elementary atomic autoionization, collision, and radiation processes, the electron-density range of interest has been subdivided into three, increasingly dense, regions. In the low-density region, which is expected to be appropriate for astrophysical plasmas such as solar flares and supernova remnants, it has been assumed that only the lowest-lying fine-structure levels of the ground-state electronic configurations of the initial ions are populated. Magnetically confined laboratory plasmas, such as tokamaks, are represented by the intermediate-densityregion, in which the initial ion populations have been assumed to be statistically distributed among all fine-structure levels of the ground-state electronic configurations. In the high-density region, which is expected to occur in laser-produced and vacuum-spark-produced plasmas, the populations of the initial ions have been assumed to be statistically distributed among all fine-structure levels of not only the ground-state electronic configurations but also the additional configurations which can be derived from the ground-state configurations by means of 2s~2p excitations. The inclusion of these additional excited configurations of the initial ions not only alters the intensities of the satellite lines that are predominant at low densities, but it also introduces additional satellite lines that occur at different wavelengths. Discussions are presented on the consequences of this electron-density sensitivity of the Ka satellite emission for the spectroscopic determinations of electron temperatures, electron densities, and charge-state distributions in both astrophysical and laboratory plasmas.