Abstract
The electron thermalization process is significant in nanosecond pulsed discharges due to the applied voltage pulse's short duration and rapid rise and fall times. In this contribution, a comparison was made between two approaches to modeling the electron kinetics of electron thermalization in atmospheric pressure helium plasma with an oxygen admixture. Modeling based on the direct solution of the local time-dependent electron Boltzmann equation was compared with modeling based on the commonly used but less general local mean energy approximation. For modeling based on the local time-dependent electron Boltzmann equation, a temporary faster decay in the population of electrons in the high energy tail and a slower decay in the population of intermediate energy electrons were observed while the electron swarm cooled from an average energy of above 8 eV, without an electric field present. During that period, the electron impact reaction rate coefficients of helium direct ionization and electronic excitation decreased by more than three orders of magnitude as compared to the modeling based on the local mean energy approximation. Global modeling of the evolution of plasma species densities in response to an electric field typical of atmospheric pressure pulsed discharges was performed with the two approaches to electron kinetics. Differences in the species densities were observed between the two approaches, with a 100% increase in the maximum density of electrons found with the modeling based on the local mean energy approximation.
Highlights
A comparison was made between two approaches to modeling the electron kinetics of electron thermalization in atmospheric pressure helium plasma with an oxygen admixture
Electron swarms were modeled being heated by a wide range of electric fields and cooling from those heated states when no electric field was present in atmospheric pressure helium plasma with an oxygen admixture
The transient energy distribution functions (EEDF) structures resulted in an increase in the average electron energy, and large differences in electron impact reaction rate coefficients
Summary
Pulsed discharges are interesting from the point of view of fundamental science as, for example, one may greatly exceed the selfsustaining voltage threshold whilst maintaining stability. Modeling of the electron thermalization process by means of the direct solution of the time-dependent electron Boltzmann equation (TDEBE), using the well known two-term approximation, was later demonstrated to be both sufficiently general and computationally inexpensive.[11]. Modeling of the electron thermalization process by means of solution of the multi-term time-dependent electron Boltzmann equation was reported using helium cross sections around the same time and compared to the two-term treatment.[13]. Global modeling of the evolution of plasma species densities in response to a time varying electric field typical of atmospheric pressure pulsed discharges experiments was performed with the two approaches to electron kinetics.
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