Modeling High‐Pressure Microplasmas: Comparison of Fluid Modeling and Particle‐in‐Cell Monte Carlo Collision Modeling

Abstract

The results of simulations using a fluid model and a PIC‐MCC model are compared, and the PIC‐MCC is used to explore the kinetics of energetic ions and electrons in microplasmas. The kinetics are studied under helium discharges at 760 Torr and Ne/Xe DBD discharges at 300 Torr with various driving currents and geometries. While EEPFs of microplasmas at high pressure show strong nonequilibrium behavior near the sheath region, EEDFs on the powered and grounded electrodes have qualitatively different features depending on input power. The effective temperature and energy flux of charged particles can be obtained from the slopes in EEPFs and IEPFs. The effects of input power, discharge length, and mixture gas concentration on the IEDFs on each electrode are discussed.

Discharge-Based Pressure Sensors for High-Temperature Applications Using Three-Dimensional and Planar Microstructures

“…They also experience much higher power densities, voltage gradients, and electric field strengths. Despite the high rate of collisions encountered at pressures approaching atmosphere, the electrons are in nonequilibrium, as they have much higher energies than the ions [7], [10], [11], [19]- [21]. When operating as glow discharges, microdischarge ionization is based on the creation of high-energy secondary electrons.…”

“…These are not considered in fluid models. Additional 1-D Monte Carlo models for steady-state microdischarges have also been developed [20], [21]. Kushner found the peak electric field near the cathode to be extremely high (over 80 kV/cm).…”

“…A significant amount of these very energetic secondary electrons, i.e., "beam electrons," are accelerated to high velocities in the positively charged sheath region proximal to the cathode. This makes the models describing microdischarges complex, as the electron energy distribution function is highly nonMaxwellian [7], [11], [20], [21]. (The distribution function in macroscale discharges is typically assumed to be Maxwellian.)…”

A Comparison of Continuum and Kinetic Simulations of Moderate pd Microplasmas Integrated With High Secondary Yield Cathodes

“…In this context, it becomes important to be able to utilize continuum microplasma models and yet be able to capture as much physics as possible which in turn requires systematic benchmarking by comparing the predictions of both computational techniques for simple geometries. While there have been a few publications dealing with comparing the results of the two different techniques, particularly for low‐pressure discharges, a systematic comparison effort has not been performed for microplasmas operating at a moderate pd ∼ 1 which would be the case when high secondary electron emitting cathodes are used. Also, in spite of highlighting some of the important differences in the solutions obtained using both techniques, limited attention has been devoted to enhance the utility of continuum models (despite the approximations involved).…”

Frequency Scaling Laws of Plasma Bulk in Atmospheric Radio Frequency Discharges

“…At atmospheric pressure collisions usually take place within a picosecond timescale and the mean free paths are reduced to nanometers scale in rf discharges, thus contrary to the case of low pressure, ions cannot earn enough energies to trigger ion‐enabled surface chemistry, thus the high flux of reactive species plays an essential role in the applications of atmospheric plasmas,15, 16 and Ohmic heating is the main way for electrons to gain energy at atmospheric pressure, which could significantly influence the frequency scalings for a given voltage or power 11, 17. These new characteristics of atmospheric rf discharges bring new challenges for experimental and computational investigation 7, 18. For example, the direct measurement of electron density below 10 12 cm −3 in atmospheric rf discharge is difficult, comparing to the case of low pressure 7.…”