Wall-induced inhomogeneities in the low-pressure Hg-Ar positive column

Abstract

Radial variations of the Hg(63P0,1,2) densities are measured in a low-pressure Hg-Ar discharge and the results are compared with a model. The 34-mm-diam discharge tube is operated in the vicinity of 400-mA current, 6.4-mTorr Hg pressure, and 2.81-Torr Ar pressure. A tunable dye laser beam passes axially through the discharge tube, and densities are measured using both a saturated absorption technique and an interference technique. The model incorporates continuity equations for Hg excited and ionic states, and a two-temperature approach to parametrizing the electron energy distribution function. The shapes of the radial density distributions of the various species are predicted rather than assumed. Considerable attention is given to the role of tail electrons above the energy threshold for Hg inelastic scattering. Theoretical considerations and the measured variations of the 63P0 and 63P2 metastable densities suggest that the tail electron temperature is lower near the wall than at the center of the discharge.

Model of a weakly ionized, low-pressure xenon dc positive column discharge plasma

“…Rate coefficients for electron impact processes are determined using Boltzmann's equation. It is here that the present computational model differs most significantly from that reported previously [5][6][7], where some functional form was assumed for the electron energy distribution (EED). Here the EED is computed using a method essentially equivalent to that described in [20].…”

“…The model is derived in part from previous models constructed to describe lowpressure rare gas/mercury positive column discharges [5][6][7]. (All references to 'mercury-based' discharges and lamps in this paper refer to low-pressure discharges where the mercury vapour pressure is 3-30 mTorr, corresponding to a density range 10 14 -10 15 cm −3 .…”

“…References [5][6][7] should be consulted for general background information on positive column discharge models of mercury-based lamps and for additional references.…”

Inhomogeneous model of an Ar–Hg direct current column discharge

“…Radially resolved experimental results show rather flat profiles of the Hg triplet states densities over the column radius, which are different than the general assumption of a Bessel profile. 70,87,88,91 A complete model would self-consistently couple the electron kinetics, the excited state population kinetics, and the radiative transfer equation including nonlocal photopumping.…”

Radiation transport coupled particle-in-cell simulation of low-pressure inductive discharges

“…The models calculate time-dependent RT using the propagator function method developed by Lawler et al, 9 and include atomic collisions between neutral species as well as electron-neutral impact collisions. In the earlier models dealing with resonance radiation transport, [10][11][12] fluid models were adopted and the redistribution of radiative state density was not evaluated with full calculation of the Holstein equation 13 but with the effective trapping factor. However, it was reported that the effective trapping factor approximation does not give accurate results when the lowest eigenmode of Holstein's solution is not the dominant one.…”