The temporal decay of the diffusion-determined afterglow plasma of the positive column

Abstract

Theoretical and experimental investigations of the afterglow decay in the diffusion-determined positive-column plasma of a neon discharge are presented. In the frame of the model the time-dependent electron Boltzmann equation, the rate equations for the neon atoms excited in the (metastable) and (resonance) level and an appropriate equation for the electric field are self-consistently solved. A radially averaged treatment has been used for the cylindrical, axially homogeneous column plasma. A detailed description of the model is given. The temporal behaviour of the decaying plasma has been calculated up to the millisecond-range. The results concerning the electron and heavy-particle kinetics have been comprehensively discussed. The analysis of the results shows that the chemo-ionization processes have an important impact. The isotropic part of the electron velocity distribution is subject to large structural changes in the temporal evolution of the decaying plasma. For higher kinetic energies two plateaux are caused as a result of the change from an active discharge plasma, driven by the electric field, to a state which is strongly determined by the action of the chemo-ionization processes. The dominant processes in the power balance of the electrons change drastically and, in the early afterglow, a slight increase of the electron density, mainly due to chemo-ionization processes, is found. The metastable neon atoms act as a power and charged-particle reservoir. In addition, probe measurements of the velocity distribution function, the density and the mean energy of the electrons have been performed in the microsecond-range of the afterglow. The experimental results are discussed and compared with the results of model calculations. The agreement between calculated and measured results is very good at steady state and satisfactory during about the first of the decay. In the further afterglow period increasing discrepancies between the results arise, which are evaluated critically with regard to various possible reasons.

Temporal dusty plasma afterglow: A review

“…Note that Eqs 14 and 15 are a very simplified picture of electron cooling. Indeed, Bräuer et al [110] showed that the electron velocity distribution function is strongly modified in the first tens of microseconds of the plasma decay and is substantially influenced by collisions between metastable atoms. Godyak [111] confirmed that the EEDF is usually different in the elastic, inelastic, and electron escape (electron with energy higher than the sheath potential) energy ranges.…”

Ac operation of low-pressure He–Xe lamp discharges

“…A self-consistent model, as presented in [23,24], which includes the time-dependent Boltzmann equation for the description of the electron kinetic properties, the system of balance equations for various heavy particles occurring in the plasma and equations for the description of an external electrical circuit, has been adopted and generalized for the current investigations.…”

Synchronous plasma enhancement in RF-driven plasma source for ion implantation

“…This relatively long plasma enhancement, produced by much shorter HV pulsed discharges (~100 ns) may be attributed to a large supplementary amount of ions and metastable atoms created during the pulse discharge, which diffuses in the RF discharge space through the grid. Metastable atoms and molecules play an important role because they supplementary sustain ionization processes acting as a power and charged particle reservoir [12][13][14].…”