Line broadening measurements and determination of the contribution of radiation diffusion to thermal conductivity in a high-pressure zinc discharge

Abstract

We investigated the broadening of spectral lines in a high-pressure zinc discharge. The contributions of resonance, van der Waals and Stark broadening are calculated and compared with broadening constants derived from side-on measurements. The energy balance is solved for a lamp containing about 1 bar metallic zinc and 2.25 bar Ar as a starting rare gas. The axis temperature of the discharge derived from the contours of the spectral lines is 5400 K as compared to model calculations yielding 5370 K. It is shown, that the contribution of radiation diffusion to the thermal conductivity is dominating at plasma temperatures above 5000 K, i.e. at temperatures, where the discharge is assumed to be in local thermal equilibrium. In a similar way as for mercury discharges, broadening of the resonance line at λ = 213.8 nm (Hg: λ = 253.6 nm) is dominant with respect to radiation diffusion, but also transitions to the triplet S4P3P and to the singlet S4P1P must be taken into account. The energy balance is solved using the measured line broadening data, resulting in a good agreement of the temperature profile with that derived from side-on measurements.

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

“…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.…”

Theoretical modeling of energy balance in electroerosion

“…We assume such temperatures following experimental data on high-pressure discharges with non-refractory materials, as reported in Ref. [10].…”

“…The electrode potential fall show dependencies on the electrode material, current density, spot temperature and plasma characteristics [10]. For tungsten the U c value seems to lie around 10 V. For copper a value of 8-9 V has been reported [5].…”

Cross sections and transport coefficients for electrons in Zn vapour

“…For mercury vapour lamps the necessary cross section and swarm transport data have been available for some time [1,2], but there is strong incentive nowadays to use a less toxic material, such as zinc. Unfortunately, as Born [3,4] points out, the required (e, Zn) data are lacking, and this paper addresses this deficiency. It is to be emphasized at the outset, however, that we are not modelling the plasma discharge in the lamp per se, but rather supplying information that may be used for this purpose.…”