Frequency effects on the electron density and α-γ mode transition in atmospheric radio frequency discharges

Abstract

In this paper, a one-dimensional model is explored to investigate the frequency effects on the characteristics of atmospheric radio frequency discharges at a given power. The simulation data and analytical results show that the improvement of electron density can be observed with better discharge stability by increasing excitation frequency in an appropriate range. Using the analytical equations deduced from the model, the mean electron density could be inferred by means of the measured parameters. The α-γ mode transition especially in high frequency discharges is also analytically discussed based on the theoretical equations.

Theoretical Study on the Characteristics of Atmospheric Radio Frequency Discharges by Altering Electrode Gap

“…To further simplify the discussion of rf discharges, in Ref. [15] we defined a new discharge parameter f p (t), namely the relaxation frequency of discharge plasmas, which reflects the timescale for space charges produced in the discharge region to disappear on the electrodes, given by…”

“…Increasing the excitation frequency can effectively raise the power density coupled to the plasmas while the discharges are still stable in the α mode, and frequency effects on the electron density and electron temperature at a fixed power have also been discussed in de-tail [14,15] . By modulating the rf discharges with pulses at repetition frequency up to hundreds of kilohertz, the atmospheric plasmas are produced only in a few of rf cycles, thus the gas heating can be lowered and power consumption is saved especially when the modulation frequency and duty cycle are optimized [16,17] .…”

The recovery of glow-plasma structure in atmospheric radio frequency microplasmas at very small gaps

“…[5][6][7] Increasing frequency is widely accepted as a way to enhance the discharge stability and reduce the electron temperature at a constant power density. [10][11][12] Nevertheless, the frequency effects on the structure transition in atmospheric rf discharges are largely unexplored. Although the microplasmas in SDP regime show many advantages and the GP structure with quasineutral plasmas may still be very useful in many applications at very small sizes.…”

“…11,12,18 In the present work, a fixed power of 2 W/cm 2 at 300 lm, namely a constant power density of 66.7 W/cm 3 , is coupled to the microplasmas while altering the excitation frequency. Fig.…”

“…2 In this letter a one-dimensional fluid model is explored to study the transition of discharge structures in capacitively rf discharges at atmospheric pressure. 11,12 Briefly, the continuity equations with the drift-diffusion approximation are used to describe the dynamic behaviors of the plasma species, and Poisson's equation is applied to obtain the electric field between the electrodes. To get the electron temperature, the energy conservation equation for electrons is also included in the governing equations; however, the gas temperature in present model is assumed to be a constant of 300 K without considering the gas heating and cooling.…”