Electron Impact Widths Research Articles

A study of ion-dynamics and correlation effects for spectral line broadening in plasma: K-shell lines

A method for the calculation of spectral line broadening in plasma has been developed and implemented. The method is based on a numerical simulation of the motion of the interacting plasma particles (both ions and electrons) and the use of the resulting time-dependent field to obtain the evolution of the radiator system. The Fourier transform of the resulting radiator time-dependent dipole function then gives the spectral line shape. This approach thus naturally accounts for all frequency regions of the plasma-particle fields and for the effects of the particle interactions on the fields. Due to a rather general approach used for solving the Schrödinger equation, the method is applicable to line-shape calculations of isolated and overlapping spectral lines involving both dipole-allowed and dipole-forbidden radiative transitions. In addition, line shapes under a simultaneous influence of externally-applied (constant or time-dependent) electric and magnetic fields can be calculated in a self-consistent manner, and polarization properties of the emitted light, caused by such external fields, can be investigated. Part of the method capabilities is demonstrated. Results presented are for spectral lines of H- and He-like ions of C, Si, and Ar in non-magnetized plasmas. It is found that ion dynamics contributes to the line broadening significantly, in several cases exceeding the electron impact widths by a few times. Also, the interactions between the radiator and the perturbers cause a significant reduction in the line widths, even for overall-weakly-coupled plasmas; a relation between this effect and the radiator–perturber coupling is made.

On the Stark broadening of Ne I lines and quasi-static versus ion impact approximation

A pulsed low-pressure capillary discharge operated in neon, helium and hydrogen gas mixture was used as the source of a high-density plasma with predominantly protons as ions for the measurement of the spectral line profiles of 13 isolated Ne I lines. An electron density of 4.8 × 1022 m−3 with an estimated uncertainty of 10% was determined from the profiles of three He I lines, while an electron temperature of 33 000 K, with an uncertainty of 12%, was measured using the relative intensities of O II impurity lines. The experimental widths of symmetric Ne I profiles are compared with data of two semiclassical calculations using quasi-static and ion impact approximations. The average ratio of measured to theoretical line widths is approximately the same for both theoretical approaches, showing good agreement in either case. This agreement with both theories must be considered, however, to be accidental, for the following reason. In one theory, the electron impact widths are relatively larger with small quasi-static ion contribution, while the other approach produces relatively smaller electron and larger ion impact widths. The asymmetric He I line profiles prove that the semiclassical theoretical approach with quasi-static ion approximation describes better the experimental Stark profiles of He I and Ne I lines. Contrary to the recently reported experimental Ne I line shapes, all studied profiles are symmetric within experimental uncertainty. Possible causes for the line asymmetry and discrepancy of Stark widths with data of this experiment are traced to the plasma source inhomogeneity and plasma diagnostics. Good agreement with several other experiments is detected.

Experimental Stark-broadening studies of the NI multiplet $\mathsf{(^{1}D) 3s^{2}D - (^{1}D)3p^{2}P^{o}}$ at 7904.5 �

Experimental Stark-broadening studies of the NI multiplet \((^{1}{\rm D})3s\) \(^{2}{\rm D} - (^{1}{\rm D})3p\) \(^{2}{\rm P}^{\rm o}\) are reported. Line shape measurements were performed using a wall-stabilized arc operated at atmospheric pressure in helium with small amounts of nitrogen and hydrogen. The radiation of the plasma emitted from nearly homogeneous plasma layers in end-on direction was measured using a grating spectrometer equipped with a charge-coupled device (CCD) detector. The arc current was varied from 35 to 50 A in order to obtain different plasma conditions (electron densities and temperatures). The so-called j(x) profiles of Griem, convoluted with the corresponding Doppler and apparatus profiles were fitted to the experimental data sets. In this way the Stark broadening parameters: the electron impact shifts (d e ) and widths (w e ) as well as ion-broadening asymmetry (A) for the investigated NI multiplet have been determined.

Stark Broadening Effect in Stellar Atmospheres: Nd ii Lines

The influence of the Stark broadening mechanism on line shapes and equivalent widths in stellar atmospheres was considered. The test of this influence was done for 38 astrophysically important Nd II lines for different types of stellar atmospheres. Moreover, the electron-impact widths for 284 Nd II lines are given. For calculation of the electron-impact widths we use the modified semiempirical method.

Advance in diagnostics for high-temperature plasmas based on the analytical result for the ion dynamical broadening of hydrogen spectral lines

It is well known that the ion dynamics is very important for Stark broadening of spectral lines in high-T plasmas. However, it is usually assumed that with the increase of the plasma density N and/or of the principal quantum number n of the upper level of the radiator, the ionic contribution to the impact width (ICIW) tends to zero. In distinction to that paradigm, by finding an analytical result for the ion dynamical broadening of hydrogen spectral lines, we show here that with the increase of N and/or n, the ICIW does not decrease. Moreover, for practically important ranges of T, N, and n, this "residual" ICIW, being virtually independent of n, can be comparable to the standard electron impact width. This result leads to: (i) a substantial revision of the past of diagnostic conclusions for a variety of high-T plasma experiments; (ii) a much better possibility to deduce from experimental, Stark-broadened line profiles not only the plasma density but also the plasma temperature; (iii) a significant enhancement of the accuracy of N and T obtained from experimental line profiles; and (iv) a substantial revision of simulation models for the ion dynamical contribution that were based on a wrong assumption that the latter vanishes under increasing N and/or n. The consequences are especially important for tokamak plasmas, where the diagnostics based on experimental profiles of high Balmer and Paschen lines is frequently used.

Advance in diagnostics for high temperature plasmas based on the analytical result for the ion dynamical broadening of hydrogen spectral lines (abstract)

It is well known that the ion dynamics is very important for Stark broadening of spectral lines in high-temperature plasmas. However, it was usually assumed that with the increase of the plasma density N and/or of the principal quantum number n of the upper level of the radiator, the ionic contribution to the impact width (ICIW) tends to zero. In distinction to that paradigm, by finding an analytical result for the ion dynamical broadening of hydrogen spectral lines, we show here that with the increase of N and/or n, the ICIW does not decrease. Moreover, for practically important ranges of T, N, and n, this “residual” ICIW, being virtually independent of n, can be comparable to the standard electron impact width. This novel result leads to: (1) a substantial revision of the past diagnostic conclusions for a variety of high-temperature plasma experiments; (2) a much better possibility to deduce from experimental, Stark-broadened line profiles not only the plasma density but also the plasma temperature; (3) a significant enhancement of the accuracy of N and T obtained from experimental line profiles. The consequences are especially important for tokamak plasmas, where the diagnostics based on experimental profiles of high Balmer and Paschen lines is frequently used.

Estimation of electron-impact line widths for singly-, doubly- and triply-charged vanadium ions

In this paper we present the electron-impact widths for 28 transitions of singly-, doubly-, and triply- ionized vanadium estimated by using the modified semiempirical method. The electron-impact widths have been estimated for the electron density of 1023m?3 and presented as a function of electron temperature.

Aspects of plasma spectroscopy: Recent advances

Two important recent developments in Stark broadening are presented in this work: The first describes the Frequency Separation Technique (FST), which is motivated by the standard electron-ion separation and has important applications in that, coupled to any of a variety of methods capable of treating the intermediate ion-dynamical regime, (but not capable of treating ion impact), presents a unified and practical solution to the ion-dynamical problem. That is, this technique allows the relaxation of the quasistatic approximation. The second describes recent improvements that allow the accurate calculation of electron impact widths.

Plasma broadening and shifting of spectral lines along the isoelectronic sequence of boron.

Temperature dependence of the Stark widths (N III and F V) and shifts (N III and O IV) of the 3${\mathit{s}}^{2}$S-3p${(}^{1}$S${)}^{2}$${\mathit{P}}^{0}$ and 3${\mathit{p}}^{2}$${\mathit{P}}^{0}$-3d${(}^{1}$S${)}^{2}$D transitions have been studied theoretically using the impact semiclassical method and experimentally observed in the plasma of a low pressure pulsed arc. Plasma electron densities were determined from the width of the He II ${\mathit{P}}_{\mathrm{\ensuremath{\alpha}}}$ line while electron temperatures were measured from the relative line intensities. To estimate the influence of different ions on the width and shift of lines, evaluations of the plasma composition data were performed and, in conjunction with our theoretical results, the contribution of ion broadening was estimated. Within the estimated uncertainties experimental Stark widths agree well with the results of our semiclassical electron impact widths in the studied electron temperature range. For the conditions of the present experiment, estimated contribution of the ion broadening has never exceeded five percent of the total width. So within the precision of this experiment it was not possible to detect its presence with certainty. Along the boron isoelectronic sequence the experimental widths and shifts agree with semiclassical electron impact data predictions. In the case of O IV lines the inclusion of the energy levels with different parent terms in our semiclassical calculations of the Stark widths and shifts improved the agreement between theory and experiment considerably. Comparisons of the experimental widths with simple theoretical formulas for estimation of plasma broadened linewidths show an agreement within estimated uncertainties. \textcopyright{} 1996 The American Physical Society.

Quantum-mechanical formulas for the electron-impact widths and shifts of isolated lines of neutral atoms and ions in plasmas

A quantum-mechanical approach is applied to calculate the widths and shifts produced by fast electron impacts of isolated lines of neutral atoms and ions. Our predictions are compared with the semiempirical formulas obtained by Griem.

Theoretical calculation of electron impact widths and shifts of XeII lines

The shifts and widths of prominent XeII transitions are calculated in the semi-empirical approach; a very good agreement with experimental values is obtained. The oscillator strengths were calculated using complete intermediate coefficients after energy matrix diagonalization.

Stark broadening of spectral lines of homologous, doubly-ionized inert gases

We report electron impact widths of 36 lines that belong to the sequence of homologous, doubly-ionized atoms of the inert gases. Only four Ar III lines in this sequence were previously measured and they are in good agreement with the present results. Good agreement is also found between these experimental results and theoretical calculations using a modified semiempirical approach. The average ratio between experimental and theoretical values is 1.06, with a maximum deviation not exceeding ±20%. We have used the present results to investigate the trends of the Stark widths of analogous lines along the homologous sequence.

Experimental study of Stark broadened N II lines from states of high orbital angular momentum

In this paper, we report experimental electron impact widths for six spectral lines belonging to 3 d-4 f transitions of singly ionized nitrogen. Line profiles were measured in a low pressure pulsed arc. An electron density in the range 5.9–7.5 × 10 22m -3 was determined from the Stark width of the He II 4686 Å line, while electron temperatures of 28,300–32,300 K were measured using relative intensities of O II impurity lines. Comparison with semiempirical theoretical results does not resolve which coupling scheme, LS or LK, is better to describe atomic states in Stark broadening calculations of certain N II lines.

Diagnostics of Pulsed Discharge Plasma in Electrolyte

AbstractTwo experimental methods are applied to determine electron temperature: the method of calculating temperature from the slope of the continuum's relative intensity, and the Boltzmann plot of the relative line intensity of oxygen OII, in a pulsed discharge in an electrolyte (PDE). Electron density is determined using the electron impact widths of magnesium ionic lines.

Electron-impact widths and shifts of neutral helium lines in a plasma

The quantum-mechanical formalism developed by Bassalo and Cattani is used to calculate the broadening and shift of many atomic lines of neutral helium in a plasma. We verify that this theory overestimates the linewidths and that it can be applied satisfactorily only to obtain the line shifts.

Electron impact widths of some Ar(II)-u.v.-multiplets

The electron impact widths of 18 Ar(II)-lines, belonging to six different multiplets, have been measured in a steady state, 1 atm arc experiment. These lines are located in the ultraviolet range of the spectrum (250–330 nm) and are observable only at high temperatures ( T⩾17,000 K). For comparison, the respective widths have also been calculated according to a simplified expression for the impact broadening of ion lines. With only one exception, excellent agreement between the experimental and the theoretical results is found. In particular, the calculations explain the experimentally observed variation of widths within a multiplet.

Stark broadening of nitrogen ion lines from states of high orbital angular momentum

Interest in the highly excited states of the nitrogen ion stems from the well-known breakdown of the validity of LS coupling, which should also affect the Stark widths of the spectral lines arising from these states when the ion is situated in a plasma. A distorted-wave calculation of the electron-impact width of the 4041 Å line is presented and compared with the results of a recent experiment as well as with calculations based upon the classical path and semi-empirical impact approximations. The latter method is used to demonstrate the effect of transformation from LS to LK coupling on the calculated Stark widths of other 3 d-4 f transitions. It is suggested that a critical experiment be undertaken to test our assertion regarding the importance of a proper description (in terms of coupling algebra) of the radiator structure in the application of Stark broadening theory to complex atoms.

Simple formulae for predicting ion linewidths including Debye shielding

We present simple formulae for use in calculating the electron-impact widths of isolated lines emitted by ionized species in cases where Debye shielding may be of importance. The various approximations made are discussed in conjunction with application of the formulae to some experimental results for singly and multiply ionized species.

The influence of elastic collisions on the broadening of ion lines

The authors have recently shown that the inclusion of hyperbolic perturber orbits considerably modifies the electron impact width and shift of an isolated ion line in the adiabatic limit. In this paper we extend these results in order to estimate the effect elastic collisions have upon the broadening parameters of several S II lines. Approximate values for the inelastic contribution to the widths of these lines are also reported and the total calculated widths are found to be in satisfactory agreement with experimental measurements. Our results show that elastic collisions constitute an important source of broadening for ion lines.

Application of a Dispersion Relation to the Electron Impact Widths and Shifts of Isolated Spectral Lines from Neutral Atoms

From a quantum mechanical dispersion relation for the scattering amplitudes of thermal electrons on excited states of emitting atoms follows a dispersion relation between electron impact widths and shifts of isolated spectral lines. This relation is used to check the consistency of previous calculations of the impact broadening made with the classical path assumption and to fully determine the parameters for the cutoff at small impact parameters in the usual perturbation theory.