Line broadening in optically thick gas discharges: Influence on plasma temperature determination

Abstract

The study of asymmetrically self-reversed lines emitted by inhomogeneous gas discharges has been made on the basis of an extension of the multiparameter method. A new procedure has been developed which makes it possible to determine the line broadening at the arc axis, its radial variation, and the ratio shift/width. An investigation is made into the effect of these quantities on the determination of the plasma temperature. The proposed method has been applied to high-pressure mercury discharges operating on dc and ac (50 Hz) using the mercury line 5461 Å. The pressure broadening in the impact approximation has been measured to be (1.43±0.11)×104 mÅ atm−1 K0.7; the corresponding line shift is towards the blue line wing.

Effect of spatial changes in broadening on self-absorbed lines and its impact on plasma diagnostics

“…While more modern line-profile formation theories are available [21][22][23], simpler models developed earlier lend themselves much more easily to useful parametrization, and are considered sufficiently reliable for present purposes. In the impact approximation suggested by the classical theory of broadening [2][3][4][5], the interaction of an emitting atom with the surrounding particles is considered as a series of separate collisions. This approximation will be used to describe the functional dependence of the line width and shift on the position.…”

“…The contribution of each broadening mechanism to the line width and shift depends on plasma conditions and line constants. According to the classical Lindolm-Foley theory of impact broadening [2,5] each one of these broadening effects as well as their simultaneous action yields a Lorentz profile. In the following, expressions for the width and shift components as well as for their combination are derived in terms of the relative temperature distribution.…”

“…The source function is closely related to the ratio of the population densities of the upper to the lower level of the emitted line and its spatial distribution characterizes the inhomogeneity of the plasma [1]. The line profile in sufficiently high-pressure and slightly ionized gas discharges, as in metal-halide arc lamps, is chiefly the result of interactions of the emitters with the surrounding neutral particles but it is also affected by electron collisions [2][3][4][5]. The contribution of the electron collisions to the line broadening increases with the electron density as in sparks, high-current pulse discharges or shock tube plasmas.…”

“…Thereby, the line profile depends on the local plasma composition and temperatures. Hence, the line profile is a position-dependent function whose, furthermore, width and shift depend on the broadening mechanisms and the constants of the specific line [2][3][4][5][6][7][8]. Analysis of a self-reversed line requires, therefore, understanding of the fundamental line-formation mechanisms and suitable relations between observed spectral intensity and spatial distributions of plasma temperatures and densities.…”

Analysis of an Inhomogeneous Semitransparent Plasma by the Lines in the Emission Spectrum

“…Among the latter, the works of Bartels [9] and Cowan and Dicke [10], in which models of the formation of lines in the emission spectrum of semitransparent plasma were proposed, as well as Preobrazhensky's works, which are partially summarized in monograph [11], are noteworthy. Subsequently, the proposed models were widely used in experimental studies, and they were modified and supplemented (see, e.g., [12][13][14][15][16][17][18]). Experimental check has demonstrated the practical applicability of the models of [9][10][11].…”