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Title: Electron trapping in radio-frequency atmospheric-pressure glow discharges

Abstract

In this letter, the authors present experimental evidence of electron trapping in radio-frequency (rf) atmospheric-pressure glow discharges. By linking electron density to nanosecond plasma images and optical emission spectroscopy, they show that electron trapping occurs under most discharge conditions. The level of electron trapping increases with increasing discharge current or/and increasing excitation frequency, and manifests itself in the change of the differential conductivity at the point of the gas breakdown. Finally, they demonstrate that electron trapping is largely related to whether the half rf period is shorter than the electron transition time across the electrode gap.

Authors:
; ;  [1]
  1. Department of Electronic and Electrical Engineering, Loughborough University, Loughborough, Leicestershire LE11 3TU (United Kingdom)
Publication Date:
OSTI Identifier:
20971781
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 90; Journal Issue: 4; Other Information: DOI: 10.1063/1.2425045; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ATMOSPHERIC PRESSURE; ELECTRODES; ELECTRON DENSITY; ELECTRONS; EMISSION SPECTROSCOPY; EXCITATION; GLOW DISCHARGES; HIGH-FREQUENCY DISCHARGES; PLASMA; PLASMA DENSITY; PLASMA DIAGNOSTICS; RADIOWAVE RADIATION; TRAPPING

Citation Formats

Liu, D. W., Shi, J. J., and Kong, M. G.. Electron trapping in radio-frequency atmospheric-pressure glow discharges. United States: N. p., 2007. Web. doi:10.1063/1.2425045.
Liu, D. W., Shi, J. J., & Kong, M. G.. Electron trapping in radio-frequency atmospheric-pressure glow discharges. United States. doi:10.1063/1.2425045.
Liu, D. W., Shi, J. J., and Kong, M. G.. Mon . "Electron trapping in radio-frequency atmospheric-pressure glow discharges". United States. doi:10.1063/1.2425045.
@article{osti_20971781,
title = {Electron trapping in radio-frequency atmospheric-pressure glow discharges},
author = {Liu, D. W. and Shi, J. J. and Kong, M. G.},
abstractNote = {In this letter, the authors present experimental evidence of electron trapping in radio-frequency (rf) atmospheric-pressure glow discharges. By linking electron density to nanosecond plasma images and optical emission spectroscopy, they show that electron trapping occurs under most discharge conditions. The level of electron trapping increases with increasing discharge current or/and increasing excitation frequency, and manifests itself in the change of the differential conductivity at the point of the gas breakdown. Finally, they demonstrate that electron trapping is largely related to whether the half rf period is shorter than the electron transition time across the electrode gap.},
doi = {10.1063/1.2425045},
journal = {Applied Physics Letters},
number = 4,
volume = 90,
place = {United States},
year = {Mon Jan 22 00:00:00 EST 2007},
month = {Mon Jan 22 00:00:00 EST 2007}
}
  • Reliable applications of atmospheric-pressure glow discharges (APGDs) depend critically on their plasma stability. A common technique of ensuring APGD stability is to keep their operation well within their stability range by decreasing their discharge current. However, this reduces the achievable densities of the reactive plasma species and, thereby, compromises the application efficiency. In this letter, the use of high excitation frequencies in radio-frequency APGD is shown to substantially expand their stability range. It is also demonstrated that high-frequency operation introduces an added benefit of higher electron energy and greater electron density, thus enabling more abundant reactive plasma species and improvedmore » application efficiency.« less
  • Discharge modes, {alpha} and {gamma}, of a radio-frequency helium capacitively coupled discharge at atmospheric pressure were investigated with the discharge gap distance between electrodes varied from 1 to 5 mm. As similarly observed in other experiments, the {alpha} and {gamma} mode and the {alpha}-{gamma} mode transition were observed with large drops in the voltage (310-179 V) and the phase angle between the voltage and current (54 deg. -18 deg. ), and a contraction of the plasma volume (8.5-0.17 cm{sup 3}, at 3 mm gap distance). The discharge voltage where the {alpha}-{gamma} mode transition occurred versus the gap distance showed amore » similar behavior with the Paschen curve for a gas breakdown. Depending on the gap distance, normal and abnormal glow regimes were observed in the {alpha}mode. At 1 and 2 mm, the {alpha} mode remained in the abnormal glow discharge until the {alpha}-{gamma} mode transition occurred as the discharge current increases. At 3 mm, however, the {alpha} mode was excited as a normal glow discharge with a constant current density (17 mA/cm{sup 2}) but it became an abnormal glow discharge as the current increased. At 4 mm, the {alpha} mode was sustained as a normal glow discharge, then the transition to the {gamma} mode occurred. Using a simple resistor-capacitor circuit model and a {alpha} sheath breakdown model, the discharge modes and the mode transition properties were studied.« less
  • In this letter, an induced gas discharge approach is proposed and described in detail for obtaining a uniform atmospheric-pressure glow discharge with air in a {gamma} mode using water-cooled, bare metal electrodes driven by radio-frequency (13.56 MHz) power supply. A preliminary study on the discharge characteristics of the air glow discharge is also presented in this study. With this induced gas discharge approach, radio-frequency, atmospheric-pressure glow discharges using bare metal electrodes with other gases which cannot be ignited directly as the plasma working gas, such as nitrogen, oxygen, etc., can also be obtained.
  • In this letter, atmospheric-pressure glow discharges in {gamma} mode with argon/nitrogen as the plasma-forming gas using water-cooled, bare copper electrodes driven by radio-frequency power supply at 13.56 MHz are achieved. The preliminary studies on the discharge characteristics show that, induced by the {alpha}-{gamma} coexisting mode or {gamma} mode discharge of argon, argon-nitrogen mixture with any mixing ratios, even pure nitrogen, can be employed to generate the stable {gamma} mode radio-frequency, atmospheric-pressure glow discharges and the discharge voltage rises with increasing the fraction of nitrogen in the argon-nitrogen mixture for a constant total gas flow rate.
  • It is widely accepted that electrode insulation is unnecessary for generating radio-frequency (rf) atmospheric pressure glow discharges (APGDs). It is also known that rf APGDs with large discharge current are susceptible to the glow-to-arc transition. In this letter, a computational study is presented to demonstrate that dielectric barriers provide an effective control over unlimited current growth and allow rf APGDs to be operated at very high current densities with little danger of the glow-to-arc transition. Characteristics of electrode sheaths are used to show that the stability control is achieved by forcing the plasma-containing electrode unit to acquire positive differential conductivity.