Eugene Oks

Review of the advanced generalized theory for Stark broadening of hydrogen lines in plasmas with tables

Abstract The Generalized Theory (GT) of Stark broadening of Stark broadening of hydrogen lines in plasmas, published by Ispolatov and Oks (JQSRT 1994; 51:19-9-38) is based on nonperturbative treatment of one component of the electron field. Therefore the GT is intrinsically more accurate than the fully-perturbative, Standard Theories (ST), such as the theory by Kepple–Griem (Phys Rev 1968; 173:317–25) (KG) and the theory by Sholin-Demura-Lisitsa (Sov Phys JETP 1973; 37:1057–65) (SDL). The present paper introduces an Advanced Generalized Theory (AGT), that yields closed-form expressions for the width, shift and coupling of Stark states. We also present tables of the AGT Stark widths of Lyman and Balmer lines for transitions with upper levels having principal quantum numbers n≤16 and for electron densities from Ne=1013 cm−3 to Ne=1020 cm−3. The mathematical simplicity of the AGT results make it possible to gain physical insight into the important features of the generalized theories that distinguish the AGT/GT from its predecessors. Empirical choices of important characteristic impact parameters made previously, are shown, using the insights possible with the AGT, to be inaccurate: (A) In the AGT, the effective Weisskopf radius ρW is proportional to n2, while SDL had empirically chosen ρW proportional to n; (B) in the AGT, the effective Weisskopf radius ρW is defined for each Stark component (i.e., dependent on the electric quantum number q), while KG had empirically chosen a component-independent ρW; (C) in the AGT the ion-field-dependent upper cutoff ρF is proportional to 1/n while KG had empirically chosen an expression for ρF proportional to 1/n2. The AGT shows that in high fields or high density range, the coupling between the ion and electron broadenings is significantly stronger than proposed by both the KG and SDL theories. Even in the low field or low density range, where the coupling between the ions and electrons broadening is negligible, the results of the AGT are more accurate than the results of the Standard Theories. In addition to yielding the effective Weisskopf radius (as noted above), the AGT can evaluate the “strong collision constant” — in distinction to both the KG and SDL theories, where the choice of this constant is empirical. The comparison of the tabulated Stark widths with the KG Stark widths indicates that the inaccuracy of the KG width is significantly increased with the increasing electron density Ne and upper principal quantum number n. However, even for the Lα line at, e.g., densities 1017 cm−3 — where the experimental width is a factor of two greater than the calculated KG width and the entire difference between the two widths was usually attributed to the ion dynamics — it turns out that the AGT eliminates about one half of this discrepancy indicating that the ion-dynamical contribution is in reality about a factor of two smaller than it was previously assumed.

A convergent theory of Stark broadening of hydrogen lines in dense plasmas

Abstract A generalized semi-classical theory of Stark broadening is developed that is free from a shortcoming of the standard semi-classical theories of Stark broadening which were intrinsically divergent at small impact parameters. A convergency of the present theory is achieved by taking into account on equal footing both a “dynamic” splitting of Stark sublevels caused by one of the components of the electron microfield and a quasistatic splitting of Stark sublevels caused by ion microfield (only the latter was allowed for in the standard theories). The presented generalized theory is developed analytically to the same level as the standard theories: it substitutes the “broadening” function C ST ( Z ) of the standard theories by a generalized but still elementary function C ( Z ). The generalized theory embraces the standard theories as one of its limiting cases corresponding to relatively low densities of a plasma. However for dense plasmas the predictions differ: our results demonstrate that the standard theories overestimate an electron impact broadening for high density plasmas.

ON THE PUZZLE OF THE OBSERVED NARROWING OF RADIO RECOMBINATION LINES

Recently, Bell et al. accurately measured in several giant H II regions both the width and the area of a great number of hydrogen radio recombination lines (RRLs)—up to the principal quantum number n = 274. For observations made at a frequency of 6 GHz, the measured line widths increased with the growth of n, but upon reaching some critical value n = ncr ~ 200, the line widths started to decrease rapidly with the further growth of n, while the line areas simultaneously increased above the predicted values. We show that the allowance for collisions with ions—especially for the transition from the impact limit of the ion Stark broadening at relatively low n to the quasi-static limit at relatively high n—could explain the puzzle of the narrowing of the RRLs observed by Bell et al.

X-ray spectral diagnostics of laser harmonic generation in the interaction of relativistic femtosecond laser pulses with clusters

It is shown that the production of X-ray emission spectra in the interaction of high-intensity laser radiation with cluster targets may be affected by the bichromatic oscillating electric field arising from the generation of the second harmonic of laser radiation. A technique is proposed for diagnosing harmonic generation in laser – cluster interactions using the spectral line profiles of multiply charged helium ions. The efficiency of second harmonic generation at a laser intensity of 3 × 1018 W cm-2 is shown to amount to about 2%.

Spectroscopic study of anomalous electric fields in peripheral regions of a current sheet plasma

We observed an unusual/anomalous asymmetry of the HeI 667.8 nm spectral line profiles emitted from the peripheral regions of a current sheet plasma, which is characterized by high electron density gradients. This asymmetry can be explained only by assuming that, in the plane perpendicular to the current in the sheet, there is a strong low-frequency oscillatory electric field, which considerably exceeds the ion electric microfield. Our calculations show that this field seems to correspond to either a circularly or nearly-circularly polarized wave in the current sheet plasma.

Spectroscopic diagnostic of Langmuir turbulence in magnetic fusion plasmas

We derive the dynamical Stark width and shift of hydrogenic spectral lines caused by Langmuir turbulence in magnetic fusion plasmas. We show that this additional broadening mechanism can dominate over the Stark broadening by the plasma microfield. Based on this analysis, we propose a method for the spectroscopic diagnostic of Langmuir turbulence in magnetic fusion plasmas.

Stark Widths of Hydrogen Spectral Lines in Plasmas: a Highly‐Advanced Non‐Simulative Semiclassical Theory and Tables

Plasma spectroscopy had served as a fertile field for applications of the formalism of Dressed Atomic States in Plasmas (DASP). The theory named in the title of this paper is based primarily on a generalization of the formalism of DASP. In its contemporary composition, this theory brings together: A) non‐impact description of the indirect coupling of the electron and ion microfields; B) non‐binary description of the direct coupling of the electron and ion microfields; C) non‐binary non‐impact description of the ion‐dynamical broadening. The latter produces, in particular, a new counter‐intuitive result for the dependence of the Ion‐Dynamical Stark Width (IDSW) on the temperature T: it predicts that in distinction to the high‐T limit, for which it was known that IDSW ∼ 1/T1/2, in the low‐T limit the temperature dependence changes to IDSW ∼ T1/4. In other words, as the temperature decreases from the high‐T limit, the IDSW first increases ∼ 1/T1/2, then reaches a maximum, and then decreases ∼ T1/4 (this bein...

A significant enhancement of high-order harmonic generation by using a dipole gas

This paper presents an analytical study of high-order harmonic generation (HHG) by quantum systems possessing permanent dipole moments (PDMs), such as atoms/molecules placed in a static electric field or polar molecules. HHG by conventional, non-PDM systems typically demonstrated a plateau in the envelope of harmonics followed by a steep fall in harmonic intensities when the harmonic number exceeds a certain threshold. This paper shows that the HHG by PDM systems results in a significant extension of the plateau to higher frequencies and a slower decline of intensities at frequencies higher than the end of the plateau . Moreover, there occurs a substantial growth of the total, summed intensity of all components of the scattering spectrum . Other physically interesting distinctive features of the HHG by PDM systems are: the presence of both odd and even harmonics of the laser frequency in the scattering spectrum; a triplet structure of both odd and even harmonics; and the appearance of a component at the doubled Rabi frequency (i.e. at a frequency much lower than the laser frequency). The results are obtained by using the adiabatic basis for the analysis of a multi-quantum resonance in a two-level system possessing PDMs.

NEW TYPE OF SHIFT OF HYDROGEN AND HYDROGENLIKE SPECTRAL LINES

Abstract A new contribution to the Center of Gravity Shift (CGS) of spectral lines in plasmas is presented: a coupled ionic-electronic shift. It originates from the coupling between the ion-quadrupole corrections to the intensities and the semiclassical electron impact shifts of individual Stark components. It is shown that this shift is the leading ionic contribution to the CGS. The new shift has a non-linear dependence on the density Ne, being proportional to N e 4 3 . Therefore its contribution relative to the pure electron shift increases with the density. Also it is shown that the well-known results on the ion quadrupole contribution to the CGS by Demura and Sholin are erroneous from both the physical and mathematical points of view.

X-ray Spectroscopy of Hot Dense Plasmas: Experimental Limits^ Line Shifts & Field Effects

High‐resolution x‐ray spectroscopy is capable of providing complex information on environmental conditions in hot dense plasmas. Benefiting from application of modern spectroscopic methods, we report experiments aiming at identification of different phenomena occurring in laser‐produced plasma. Fine features observed in broadened profiles of the emitted x‐ray lines and their satellites are interpreted using theoretical models predicting spectra modification under diverse experimental situations.