On the decay of metastable and resonance Xe atoms in the afterglow of a constricted discharge

Abstract

The radial and temporal dependences of the metastable 6 3P2 (Xem) and resonance 6 3P1 (Xer) state densities are measured in the active phase and afterglow of pulsed discharge in xenon by laser absorption technique at pressure 10 Torr and currents 200–500 mA. It is found that the densities grow by a factor of 25 during the transition from the active discharge phase to the afterglow and there is no decrease of the density after switching the field off. It is shown that the collisional-radiative recombination prevails over the dissociative recombination because of high electron density and relatively low electron temperature in a constricted discharge. The electron cooling after the field switching-off is caused mainly by electron–ion collisions whereas the electron–atom elastic collisions are less effective due to the Ramsauer effect. The quantitative modelling of the active phase and afterglow is performed on the basis of the time-dependent system of balance equations for densities of excited atoms and charged particles, as well as electron temperature. The results of the modelling reflect all peculiarities of the excited atom behaviour both in the active phase and afterglow.

Study of pulsed neon–xenon VUV radiating low pressure plasmas for mercury free fluorescent sign optimization

“…The temporal evolution of the electron temperature, that is the fast decreasing during the first fifty microseconds during the afterglow, was shown to be crucial in the fit of the experimental records. It could be pointed out that such rapid thermalization of electron population was previously documented in [17] where the large xenon density growth at the onset of the afterglow was connected with a two times reduction of the electron temperature within a 20 µs duration, this evolution being very close to that inferred in our study to achieve the best fit between calculation and experimental data.…”

“…It appears that the recombination of our pulsed neon xenon plasma, produced with xenon partial pressure of about 0.5 mbar, occurs at electron temperature lower than 0.7 eV, electron density of a few 10 11 cm -3 , and essentially involves dissociative recombination reactions. This regime appears in between the previously reported and modelled xenon low pressure (0.07 mbar), high density (a few 10 14 cm -3 ), low electron temperature (below 1 eV) and the constricted high xenon pressure (13 mbar), low electron density (10 11 cm -3 ) and high electron temperature (3.5 eV) modes of operation of pulsed low voltage discharges [17]. The model also confirms the fast decrease of the electronic temperature after the current pulse end, as the best fit were obtained if the temperature falls from 0,7 eV at the end of the pulse down to a few tenths of eV in the first tens of microseconds during the afterglow.…”

Charged particle kinetics and gas heating in CO2 microwave plasma contraction: comparisons of simulations and experiments

“…Specifically, based on recent studies on atomic plasmas, two different mechanisms have been identified as responsible for plasma contraction: (i) electron-electron collisions, or (ii) non-uniform gas heating along the tube radius. The role of electron-electron collisions has been investigated by Golubovskii et al [31] and by Petrov and Ferreira [32], with the conclusion that these collisions have an important influence on the electron energy distribution function (EEDF) and, in turn, on increasing electron impact ionization rate coefficients in the plasma core and not on the edges. The non-uniform gas heating along the discharge radius has been considered by Martinez et al [33], by Ridenti et al [34], and by Moisan and Pellettier [35] as the main mechanism driving contraction in Ar, Ne and N 2 MW plasmas.…”