Modeling of microplasmas from GHz to THz

Abstract

We present a study of atmospheric-pressure microdischarges sustained over a wide range of continuous excitation frequencies. A fluid model is used to describe the spatial and temporal evolution of the plasma properties within a 200 μm discharge gap. At 0.5 GHz, the behavior is similar to a typical rf collisional discharge. As frequency increases at constant power density, we observe a decrease in the discharge voltage from greater than 100 V to less than 10 V. A minimum of the voltage amplitude is attained when electron temporal inertia delays the discharge current to be in phase with the applied voltage. Above this frequency, the plasma develops resonant regions where the excitation frequency equals the local plasma frequency. In these volumes, the instantaneous quasi-neutrality is perturbed and intense internal currents emerge ensuring a low voltage operation range. This enhanced plasma heating mechanism vanishes when the excitation frequency is larger than the local plasma frequency everywhere in the plasma volume. For a typical peak electron density of 5×1020 m−3, this condition corresponds to ∼0.2 THz. Beyond the plasma frequency, the discharge performs like a low loss dielectric and an increasingly large voltage is necessary to preserve a constant absorbed power.

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

“…For the continuum simulations, we employed a plasma fluid model which is essentially derived by taking velocity moments of the Boltzmann equation coupled with the Poisson's equation and closely follows the description by Fitzpatrick . Our model also resembles several other fluid models for low‐temperature plasmas (and has been verified using results from these publications) but is described here for self‐sufficiency.…”

Microplasma thruster powered by X-band microwaves

“…X-band microwaves have been employed to generate highdensity, high-temperature plasmas under electron cyclotron resonance conditions at low pressures (∼10 −5 -10 −4 Pa) for use of highly charged ion and short wavelength radiation sources; [72][73][74] and a few studies have been concerned with plasma discharges at higher and atmospheric pressures (∼1-50 kPa) where the plasma is highly collisional. 75 Microwave frequency effects on plasma discharges have recently attracted much attention to generate higher density nonthermal microplasmas at atmospheric pressures, [76][77][78][79][80] from the viewpoint of a fundamental interest in plasma physics/ chemistry as well as their applications such as materials FIG. 1.…”

“…processing, chemical synthesis, and plasma medicine. However, these studies of microplasmas driven by X-band and much higher frequency microwaves have focused on microstrip-based implementations with interelectrode gaps, [76][77][78][79][80] where electrons and ions are assumed to be confined in the gap by oscillating electric fields, which results in particle losses to the walls to become negligible, and thus leads to an increase in plasma density. 79 Little research has been conducted on surface waveexcited microplasmas as well as SWPs of conventional scale driven by X-band microwaves.…”

Benchmark continuum and kinetic simulations of argon microplasmas in the direct current and microwave regimes

“…These conditions are similar to the operating parameters of split-ring resonator microplasma devices that have been extensively tested by Hopwood et al (for example [35][36][37][38]). One-dimensional fluid simulations have also been reported [39,40] based on the drift-diffusion model (using an effective electric field approach) for the electrons and the fullmomentum equation for ions (that are more or less stationary under these conditions). The secondary electron emission was set to be equal at both electrodes for the PIC-MCC and continuum simulations reported here.…”