Ne IX line G -ratio in a non-Maxwellian and anisotropic plasma

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A new asymmetry parameter characterizing the differences between the polarized π and σ gain components of the soft-x-ray J=0-1 lasing line of neon-like ions is calculated in the case of Ge 22+ assuming an electron distribution which is a weighted sum of an isotropic Maxwellian and a monoenergetic beam. Using a quasi steady-state collisional-radiative model, we determine in the weak amplification regime the relative populations of the upper M=0 and lower M 0, 1 =  magnetic sublevels of the lasing line as a function of electron density from 10 20 to 2 10 21 ´cm −3 . This model includes inelastic and elastic collisional transitions, as well as spontaneous radiative decay between all the 337 M-sublevels arising from the 75 lowest-lying Ge 22+ J-levels. The computations were performed for a temperature T e of the Maxwellian component between 1.2 10 6 ´and 8 10 6 ´K, a kinetic energy E 0 and a fraction f of the beam component in the ranges 1.5 20 keV -and 0.1% 10% -, respectively. The basic atomic data, such as level energies, radiative decay probabilities and inelastic collision strengths, were calculated with the flexible atomic code. However, some modifications of this code were made to get the collision strengths for transitions between M-sublevels due to impact with isotropic electrons as well as due to impact with an electron beam in the case of de-excitation. We find that the newly introduced asymmetry parameter may become significant under certain conditions of electron distribution corresponding to relatively low T e (1.2 10 2.5 10 6 6´-K) and E 0 (3-6 keV). The results reported here may be useful in the evaluation of the polarization degree of the J=0-1 x-ray laser output from a germanium plasma in the presence of fast directional electrons.

Section: Rate Coefficients For Collisional Transitions Between Magnet...mentioning

confidence: 99%

Collisional-radiative calculations for theJ= 0−1 lasing line of neon-like germanium under anisotropic excitation conditions

Bentotoche

Inal

Benmouna

2018

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“…Over the past several decades, extensive investigations have been carried out in order to understand the patterns of fluorescence radiation after the electron-impact excitation (EIE) of highly charged ions [7][8][9][10][11]. The first measurement of the polarization was made in the experiment on the detection of photons emitted from transitions in He-like Sc 19+ ion by using an electron beam ion trap (EBIT) at two electron-beam energies of 4.36 and 5.62 keV [12].…”

Section: Introductionmentioning

confidence: 99%

Local time dependence of the magnetic sublevel population and polarization of fluorescence radiation

Chen¹

2019

We investigate the time-dependence magnetic sublevel population and polarization of x-ray photoemission for the 1s2p 3P2,1 → 1s2 1S0 lines of an exemplary ion Fe24+ due to impact excitation by a longitudinally polarized electron beam. The analysis is performed based on the fully relativistic distorted-wave approximation and the magnetic sublevel-to-magnetic sublevel collisional-radiative model. The radiative cascade process and Breit interaction are considered to make the results more precise. The time evolution of the magnetic sublevel populations and circular polarization properties are discussed. Our results reveal for the first time that the variations of the magnetic sublevel populations demonstrate a pattern when the time is shorter than 103 ps; some of the populations increase rapidly, while the others remain relatively constant. These dramatic influences also bring about notable changes in the polarization properties of fluorescence emission. We compare our results with other theoretical predictions and find good consistency. This work provides new insight into the fundamentals of x-ray radiation and further prompts the application of fluorescence polarization in plasma diagnostics.

“…The third term describes the contribution to the 2 P M J f population arising from cascades from higher magnetic sublevels D J M k k k . A and C are, respectively, the transition rate (s −1 ) and the collisional excitation rate coefficient (cm 3 s −1 )[32][33][34][35]…”

mentioning

confidence: 99%

Dominance of the density effects in the magnetic sublevel population and circular polarization of x-ray radiation

Chen¹

2019

On the basis of the fully relativistic distorted-wave treatment of impact excitation by a longitudinally polarized electron beam, we have assessed the influence of density effects on the magnetic sublevel population and circular polarization of x-ray radiation, taking the 1s2p 3P2 1s2 1S0 line of selected He-like Ne8+, Ar16+, and Kr34+ ions as an example. Starting from the most general method of rate equation, we carried out specific analytic expressions in terms of the magnetic sublevel-to-magnetic sublevel collisional-radiative model, corresponding to different states. It is shown that the density contributions to the magnetic sublevel population can be considerable. These dramatic influences also lead to a remarkable decrease in the circular polarization of x-ray radiation, yet the character of which weakens as the incident energy and/or atomic number increases. The Breit interaction and radiative cascade contributions are also estimated, and found to be generally important in these systems. These findings originate a better understanding of the fundamentals of x-ray radiation arising from various kinds of plasmas. Comparisons of our results with other theoretical predictions, when available, are made.