Shou-Zhe Li

Influence of oxygen in atmospheric-pressure argon plasma jet on sterilization of Bacillus atrophaeous spores

A nonequilibrium Ar∕O2 plasma discharge at atmospheric pressure was carried out in a coaxial cylindrical reactor with a stepped electrode configuration powered by a 13.56MHz rf power supplier. The argon glow discharge with high electron density produces oxygen reactive species in large quantities. Argon plasma jets penetrate deep into ambient air and create a path for oxygen radicals to sterilize microbes. A sterilization experiment with bacterial endospores indicates that an argon-oxygen plasma jet very effectively kills endospores of Bacillus atrophaeus (ATCC 9372), thereby demonstrating its capability to clean surfaces and its usefulness for reinstating contaminated equipment as free from toxic biological warfare agents. The decimal reduction time (D values) of the Ar∕O2 plasma jet at an exposure distance of 0.5–1.5cm ranges from 5 to 57s. An actinometric comparison of the sterilization data shows that atomic oxygen radicals play a significant role in plasma sterilization. When observed under a scannin...

Comparison of atmospheric-pressure helium and argon plasmas generated by capacitively coupled radio-frequency discharge

In this paper, the electrical discharge characteristics of plasmas generated in coaxial cylindrical electrodes capacitively powered by a radio-frequency power supply at atmospheric pressure are investigated with respect to helium and argon gases. The electrical discharge parameters, voltage (V), current (I), and power (P), are measured for both helium and argon plasmas, and the electron temperatures and electron densities for them are evaluated by means of the equivalent circuit model and the power balance equation. By comparison of the discharge characteristics of the helium and argon plasmas, it is found that the discrepant macroscopic characteristics of helium and argon plasma, viz., current and voltage characteristics and current and power characteristics, are owed to their own intrinsic microscopic parameters of the helium and argon atoms, such as the first excited energy, the ionization energy, the total cross section, and the atom mass. Furthermore, the influences of the additive gas, oxygen gas, o...

Optical diagnosis of an argon/oxygen needle plasma generated at atmospheric pressure

An atmospheric-pressure argon/oxygen needle plasma discharge is generated in a long dielectric tube and investigated with respect to its electrical characteristics and the production of oxygen atom by means of optical actinometry. The length of discharge column depends on the operating frequency and applied voltage of power supply, which is interpreted qualitatively with an equivalent circuit model. Moreover it is found that there exists an optimal value of oxygen concentration in the production of oxygen radicals. At last, the oxygen/argon plasma is employed to modify the interior surface of a fine quartz tube to demonstrate its potential applications.

A homogeneous dielectric barrier discharge plasma excited by a bipolar nanosecond pulse in nitrogen and air

In this paper, a nanosecond bipolar pulse voltage with 20?ns rise time is employed to generate a low gas temperature homogeneous dielectric barrier discharge plasma both in nitrogen and air at atmospheric pressure. Images of the discharge, waveforms of pulse voltage and discharge current, and the optical emission spectra emitted from the discharge are recorded successfully under severe electromagnetic interference. The effects of pulse peak voltage, pulse repetition rate and the gap distance between electrodes on gas temperature and the emission intensities of NO (A?2????X?2?), OH (A?2????X?2?) and N2 are discussed. It is found that the emission intensities of NO (A?2????X?2?), OH (A?2????X?2?) and N2 rise with increasing both pulse peak voltage and pulse repetition rate but decrease with gap distance between the electrodes when it is above 2.5?mm. The effect of concentrations of O2 on the emission intensities of NO (A?2????X?2?), OH (A?2????X?2?) and N2 is also investigated, and it is found that the emission intensities of both NO (A?2????X?2?) and OH (A?2????X?2?) reach maximum values when the O2 concentration is 0.3%.

Self-organized pattern formation of an atmospheric pressure plasma jet in a dielectric barrier discharge configuration

This letter reports the observation of self-organized patterns formed in a 29mm wide atmospheric pressure plasma jet. By altering the gas flow rate and/or the applied voltage, the plasma jet is seen to have at least three different modes, namely, a diffuse-looking discharge, a self-organized discharge, and an unstable discharge with randomly occurring plasma channels. The self-organized discharge mode is characterized by several bright plasma channels embedded in a diffuse and dim plasma background. These plasma channels are regularly spaced from each other and their self-organized patterns are shown to evolve abruptly.

The effect of gas flow on argon plasma discharge generated with a single-electrode configuration at atmospheric pressure

A long atmospheric-pressure plasma column confined in a dielectric tube is generated in argon with use of a single-electrode configuration driven with a sinusoidal power supply operating at 45 kHz. The electrical characteristics are investigated by means of measuring voltage-current and voltage-power curves at two gas flow states, turbulent and laminar. The gas temperatures of plasma discharge at various gas flow rates are determined by the spectroscopic analysis of OH A-X spectrum. The discussion about effect of gas flow on electrical discharge characteristics is presented and it is found that the heat removal by gas flow plays the most important role in determining its electrical characteristics.

Uniform glowlike plasma source assisted by preionization of spark in ambient air at atmospheric pressure

The ultraviolet radiation produced by spark discharges is employed to supply preionization for the dielectric barrier discharge in ambient air at atmospheric pressure. The effect of ultraviolet preionization and overvoltage on improving the uniformity of the dielectric barrier discharge is investigated experimentally. Based on the emission spectra and voltage-current wave forms, the optical and electrical characteristics of the discharge are discussed.

Atmospheric-pressure argon/oxygen plasma-discharge source with a stepped electrode

The nonequilibrium glow discharge in argon mixed with oxygen at atmospheric pressure was generated in a parallel plate reactor with a stepped electrode powered by a 13.56MHz radio-frequency power supplier. The stepped-electrode reactor consists of a narrow and wide gap structure. A strong electric field occurred at the narrow gap region preionizes Ar∕O2 gas and assists to generate a large volumetric plasma in the wide gap region. Therefore, the stepped-electrode reactor makes it easy to operate Ar∕O2 glow discharge, providing a stable, uniform, and broad plasma jet at atmospheric pressure.

Discharge characteristics of an atmospheric-pressure argon plasma column generated with a single-electrode configuration

An atmospheric-pressure argon discharge plasma column is generated by making use of a single-electrode configuration with the power supply operating at a frequency of 45 kHz. It is observed that corona, glowlike plume, and filamentary discharges evolve individually with increasing applied voltage. It is in the filamentary state with average electron density of order 1012 cm−3 that plasma column grows up in the tube with increasing applied voltage. Its discharge characteristics are determined by measuring electrical parameters (voltage, conduction current, and average absorbed power) and optical emission spectroscopy.

A pulse-modulated nonequilibrium atmospheric-pressure microwave argon plasma discharge preionized by a kilohertz excited plasma jet

A pulse-modulated nonequilibrium atmospheric-pressure microwave argon surface wave plasma is generated by means of a preionization discharge with a single-electrode plasma jet driven by a power supply of 50 kHz. It is found that the electron induced Saha-like balance dominates excitation process in the plasma discharge through the electron temperature varying with the microwave input power and the applied voltage of kilohertz power supply. The microwave pulse-modulating effect on nonequilibrium characteristics of dual-frequency exciting argon surface wave plasma is studied by spectroscopic measurement of the excitation temperature and gas temperature.