Variation of the oscillator strengths for the α emission lines of the one- and two-electrons ions in dense plasma

Abstract

We present the results of a detailed theoretical study on the variation of the oscillator strengths for the 1s ! 2p transition of the H-like ions and the 1s 2 1 S ! 1s2p 1 P transition of the He-like ions (or, inversely, the Lyman-a and He a emission lines, respectively) subject to external plasma which meet the spatial and temporal criteria of the Debye-H€ uckel (DH) approximation. Our study shows that the resulting oscillator strength decreases for the He a line for He-like ions, similar to the Lyman-a emission lines for all H-like ions, as the effect of the external plasma increases with the decreasing Debye length D in terms of a reduced Debye length k D ¼ Z eff D. A nearly universal feature is demonstrated for a scaled oscillator strength as a function of the reduced Debye length k D ¼ (Z À 1)D for different He-like ions that meet the same criteria for the DH model. The percentage changes of the oscillator strengths from their plasma-free values are substantially greater than those for the corresponding change for the redshifts of the Lyman-a and He a emission lines subject to outside dense plasma. Should these general features be demonstrated experimentally, the theoretical procedure presented in this study could easily be applied to extrapolate from a single calculation for one He-like ion to other He-like ions, which could offer an alternative to complement other diagnostic efforts of the dense plasma.

Variation of the transition energies and oscillator strengths for the 3C and 3D lines of the Ne-like ions under plasma environment

“…This limited DH approximation has generated the redshift of the Lyman-α line of the H-like ion in a plasma environment in agreement both with the experimentally observed value and the data from more elaborate simulations based on quantum mechanical approaches [28]. Its applications to the α emission lines of both hydrogen and helium-like ions which meet the spatial and temporal criteria have also led to simple scaling properties of the redshifts of the transition energies as well as the oscillator strengths [21,28,29]. For more complex ions, it is expected that a full-relativistic application of the DH approximation is necessary to include the electron correlations as well as the relativistic effects.…”

“…For the relatively simple atomic systems, such as the H-like and He-like ions with relatively small Z in our recent studies [21,28,29], the relativistic effect is negligible and the non-relativistic calculations should be adequate. But, in a more complex system with more electrons such as the Ne-like ions in the present calculation, the relativistic effects become important and should be taken into account.…”

“…Although many studies were carried out recently to identify the reasons for such discrepancies, it remains as an open question [15][16][17][18][19][20]. Meanwhile, a recent study has demonstrated a substantial variation of the oscillator strengths for the α-line of the H-like and He-like ions subject to outside dense plasmas [21].One of the main objectives of this work is to find out if such variation in the oscillator strengths, in particular the 3C/3D intensity ratio of the Ne-like ions, could also be shown in dense plasma environment.…”

“…The influence of the plasma environment to the atomic processes is a challenging many-body problem and several sophisticated and complicated models were developed over the years to understand such processes [22][23][24][25]. On the other hand, the Debye-Hückel (DH) model, with its simplicity [26], could easily capture the important qualitative features over several orders of magnitude in plasma temperature and density, and, at the same time, offer the physical interpretation as a reliable reference for other theoretical models [21,[27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46]. Recently, we present a critical assessment of the DH approximation in terms of the spatial and temporal criteria for dense plasma which limits its applicability to atomic processes that are short-ranged in nature for the H-like and Helike ions with nucleus charge Z between 5 and 18 [21,28,29].…”

“…On the other hand, the Debye-Hückel (DH) model, with its simplicity [26], could easily capture the important qualitative features over several orders of magnitude in plasma temperature and density, and, at the same time, offer the physical interpretation as a reliable reference for other theoretical models [21,[27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46]. Recently, we present a critical assessment of the DH approximation in terms of the spatial and temporal criteria for dense plasma which limits its applicability to atomic processes that are short-ranged in nature for the H-like and Helike ions with nucleus charge Z between 5 and 18 [21,28,29]. This limited DH approximation has generated the redshift of the Lyman-α line of the H-like ion in a plasma environment in agreement both with the experimentally observed value and the data from more elaborate simulations based on quantum mechanical approaches [28].…”