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Title: Mode transition in radio-frequency atmospheric argon discharges with and without dielectric barriers

Abstract

In this letter, basic characteristics of glow modes and their mode transition are studied for radio-frequency (rf) atmospheric argon discharges with bare and dielectrically insulated electrodes. Through input power control, large-volume rf atmospheric argon discharges with bare electrodes are achieved in the {alpha} mode via an abrupt transition from a constricted {gamma} mode, whereas dielectrically insulated electrodes result in large argon discharges in both the {alpha} and {gamma} modes with gradual mode transition. Current dependence of the 750 nm line intensity and of the gas temperature are shown to capture clearly the signature of mode transition.

Authors:
;  [1]
  1. Department of Electronic and Electrical Engineering, Loughborough University, Loughborough, Leicestershire LE11 3TU (United Kingdom)
Publication Date:
OSTI Identifier:
20971861
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 90; Journal Issue: 10; Other Information: DOI: 10.1063/1.2711413; (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; ARGON; BOUNDARY LAYERS; DIELECTRIC MATERIALS; ELECTRODES; ELECTRON TEMPERATURE; GLOW DISCHARGES; HIGH-FREQUENCY DISCHARGES; ION TEMPERATURE; PLASMA; PLASMA INSTABILITY; RADIOWAVE RADIATION

Citation Formats

Shi, J. J., and Kong, M. G.. Mode transition in radio-frequency atmospheric argon discharges with and without dielectric barriers. United States: N. p., 2007. Web. doi:10.1063/1.2711413.
Shi, J. J., & Kong, M. G.. Mode transition in radio-frequency atmospheric argon discharges with and without dielectric barriers. United States. doi:10.1063/1.2711413.
Shi, J. J., and Kong, M. G.. Mon . "Mode transition in radio-frequency atmospheric argon discharges with and without dielectric barriers". United States. doi:10.1063/1.2711413.
@article{osti_20971861,
title = {Mode transition in radio-frequency atmospheric argon discharges with and without dielectric barriers},
author = {Shi, J. J. and Kong, M. G.},
abstractNote = {In this letter, basic characteristics of glow modes and their mode transition are studied for radio-frequency (rf) atmospheric argon discharges with bare and dielectrically insulated electrodes. Through input power control, large-volume rf atmospheric argon discharges with bare electrodes are achieved in the {alpha} mode via an abrupt transition from a constricted {gamma} mode, whereas dielectrically insulated electrodes result in large argon discharges in both the {alpha} and {gamma} modes with gradual mode transition. Current dependence of the 750 nm line intensity and of the gas temperature are shown to capture clearly the signature of mode transition.},
doi = {10.1063/1.2711413},
journal = {Applied Physics Letters},
number = 10,
volume = 90,
place = {United States},
year = {Mon Mar 05 00:00:00 EST 2007},
month = {Mon Mar 05 00:00:00 EST 2007}
}
  • 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.
  • An experimental investigation is presented to characterize the dependence of discharge operation modes ({alpha} and {gamma} modes) and their transition on excitation frequency in radio-frequency atmospheric argon glow discharges. The current-voltage characteristics are used to distinguish the {alpha} and {gamma} modes at an excitation frequency range of 5-24 MHz. The operation regime of {alpha} mode with stable and uniform discharge in large volume is found to expand at higher excitation frequency. It is shown that, when excitation frequency is below 10 MHz, the discharge evolves directly into {gamma} mode after gas breakdown and, when excitation frequency is above 10 MHz,more » the discharge operates in the coexistence mode of {alpha} and {gamma} after mode transition.« less
  • In this letter, an experimental investigation is presented to characterize the properties and benefits of radio-frequency (rf) dielectric-barrier discharges (DBDs) in atmospheric argon. Compared to rf atmospheric glow discharges generated with bare electrodes, atmospheric argon rf DBDs are shown to remain stable and uniform over a large current range from the {alpha} and the {gamma} modes. Optical emission spectroscopy is used to show an active underpinning plasma chemistry and a gas temperature range of 461-562 K. These highlight the advantages of argon rf DBD as a surface processing technique over more expensive helium-based rf atmospheric glow discharges.
  • 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 {alpha}-{gamma} mode transition especially in high frequency discharges is also analytically discussed based on the theoretical equations.
  • To investigate the transition from the low density mode to the high density mode in an electron cyclotron resonance (ECR) discharge, a Langmuir probe and an {ital E} field probe were used to measure ion density and {ital E} field intensity as functions of axial position and power. The experiments were performed in argon at 0.13 Pa in a 7.9 cm diam cyclindrical source chamber propagating TE{sub 11} mode 2.45 GHz microwave power. Low mode was characterized by a standing wave throughout the plasma chamber and minimal power absorption. High mode exhibited nearly complete power absorption and no standing wavemore » past the ECR zone. A sliding short (ss) was used to determine if the position of an {ital E} field null in the source chamber affected the transition between these two modes for various magnetic field configurations. The ss position had little effect on mode transition, relative power absorption or ion density when positioned downstream from a broad, large volume resonance zone (resonance near the mirror midplane). However, the plasma could not be ignited if the short was placed at or upstream from the large volume resonance zone.« less