Influence of electron scattering and energy partition method on electron transport coefficient

Abstract

The veracity of a low temperature plasma model is limited by the accuracy of the electron transport coefficient, which can be solved by simulating the electron transport process. When simulating the transport properties of electrons, there are a variety of approaches to dealing with the scattering of electrons and energy partition between the primary-electrons and secondary-electrons after electron-neutral particles’ collision. In this paper used is a model based on the Monte Carlo collision method to investigate the influence of scattering method and energy partition method on the electron transport coefficient. The electron energy distribution function, electron mean energy, flux mobility and diffusion coefficients, as well as the Townsend ionization coefficients are calculated in the hydrogen atom gas under a reduced electric field from 10 to 1000 Td. The calculation results show that the influence of the isotropic scattering assumption on the electron transport coefficients increases with reduced electric field increasing. However, even under a relatively low reduced electric field (10 Td), the calculated mean energy, flux mobility, and flux diffusion coefficient of electrons under the assumption of anisotropic scattering are 39.68%, 17.38% and 119.18% higher than those under the assumption of the isotropic scattering. The different energy partition methods have a significant influence on the electron transport coefficient under a medium-to-high reduced electric field (> 200 Td). Under a high electric field, the mean energy, flux mobility and flux diffusion coefficient calculated by the equal-partition method (the primary and secondary electrons equally share the available energy) are all less than the values from the zero-partition method (the energy of secondary-electrons is assigned to zero). While the change of Townsend ionization coefficient with reduced electric fields shows a different trend. The electron transport coefficient obtained by the Opal method lies between the values from the equal-partition method and the zero-partition method. In addition, considering the anisotropic scattering, the influence of energy partition method on the transport coefficient is higher than that under the assumption of isotropic scattering. This study shows the necessity of considering the anisotropic electron scattering for calculating the electron transport coefficient, and special attention should be paid to the choice of energy partition method under a high reduced electric field.

A tutorial overview of the angular scattering models of electron–neutral, ion–neutral, neutral–neutral, and Coulomb collisions in Monte Carlo collision modeling on low-temperature plasma

“…The MC swarm calculation is also performed by an inhouse PIC-DSMC code with the implemented anisotropic ionization model, which is initially designed for simulation on vacuum arcs [122][123][124]. The electron number is not fixed during ionization [25]: the initial electron number is 10 4 , and the simulation stops if the electron number reaches 10 7 . Similar results are obtained to those shown in figure 3.…”

“…The second reason is the lack of analytically simpleto-use models of DCS, through which scattering angles can be randomly sampled by easy inversion instead of the timeconsuming accept-reject method. During the last two decades, different angular scattering models have been compared in various scenarios, such as electron transport study, ionization source terms in glow discharge, thermal runaway electrons in streamer discharge, and interstellar neutral atoms in the outer heliosheath [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. It was found that the angular scattering model is a non-trivial topic.…”