Chunsheng Ren

A simple cold Ar plasma jet generated with a floating electrode at atmospheric pressure

An experimental study is presented of a cold atmospheric Ar plasma jet with distinct advantages of low-working voltage and high plasma stability. To effectively improve the performance of the jet, a pair of pin electrodes with one floating in the air is applied. Variation in the applied voltage and/or the Ar gas flow causes the transition of the jet plasma from ignition, through stable plume to an unstable stage. The characteristics of the jet discharge are also studied by means of the electrical and spectroscopic diagnosis.

Spatially extended atmospheric plasma arrays

This paper reports a systematic study of spatially extended atmospheric plasma (SEAP) arrays employing many parallel plasma jets packed densely and arranged in an honeycomb configuration. The work is motivated by the challenge of using inherently small atmospheric plasmas to address many large-scale processing applications including plasma medicine. The first part of the study considers a capillary–ring electrode configuration as the elemental jet with which to construct a 2D SEAP array. It is shown that its plasma dynamics is characterized by strong interaction between two plasmas initially generated near the two electrodes. Its plume length increases considerably when the plasma evolves into a high-current continuous mode from the usual bullet mode. Its electron density is estimated to be at the order of 3.7 × 1012 cm−3. The second part of the study considers 2D SEAP arrays constructed from parallelization of identical capillary–ring plasma jets with very high jet density of 0.47–0.6. Strong jet–jet interactions of a 7-jet 2D array are found to depend on the excitation frequency, and are effectively mitigated with the jet-array structure that acts as an effective ballast. The impact range of the reaction chemistry of the array exceeds considerably the cross-sectional dimension of the array itself, and the physical reach of reactive species generated by any single jet exceeds significantly the jet–jet distance. As a result, the jet array can treat a large sample surface without relative sample–array movement. A 37-channel SEAP array is used to indicate the scalability with an impact range of up to 48.6 mm in diameter, a step change in capability from previously reported SEAP arrays. 2D SEAP arrays represent one of few current options as large-scale low-temperature atmospheric plasma technologies with distinct capability of directed delivery of reactive species and effective control of the jet–jet and jet–sample interactions.

A two-dimensional cold atmospheric plasma jet array for uniform treatment of large-area surfaces for plasma medicine

For plasma treatment of inanimate surfaces and living tissues in medicine, it is important to control plasma–sample interactions and to mitigate non-uniform treatments of usually uneven sample surfaces so that effectiveness of application can be reproduced for different biological samples, relatively independently of their varying surface topologies and material characters. This paper reports a scalable two-dimensional (2D) array of seven cold atmospheric plasma (CAP) jets intended to achieve these two important requirements as well as to address the unique challenge of jet–jet interactions. While the CAP jet array can be configured to interact with a biological sample in either a direct mode (used with an in situ sample) or a remote mode (used as an afterglow), this study focuses on the direct mode. Using a downstream planar electrode as a sample model, the spatial distribution of reactive species and electrons delivered by individual jets of the 2D CAP jet array attains excellent uniformity. Specifically, the spatial variation over 100 μs is 5.6 and 7.9%, respectively, for wavelength-integrated optical emission intensity, and for atomic oxygen emission intensity at 845 nm when the oxygen admixture is 0.5% of the helium carrier gas. It is also shown that the highest emission intensity at 845 nm occurs at O2/He=0.5% under the best jet–jet uniformity conditions for O2/He=0.3–0.7%. These results indicate the potential of 2D CAP jet arrays for uniform treatment and for effective control of jet–jet interactions. Furthermore, spatial uniformity is accompanied by rich dynamics of jet–jet interactions and jet–sample interactions. Of the honeycomb-arranged seven CAP jets, the central jet is strongest in the negative half cycle, whereas the six surrounding jets (of uniform strength) are strongest in the positive half cycle. These dynamic features offer possible insights with which to better control jet–jet interactions and plasma–surface interactions in future.

Stark broadening measurement of the electron density in an atmospheric pressure argon plasma jet with double-power electrodes

Characteristics of a double-power electrode dielectric barrier discharge of an argon plasma jet generated at the atmospheric pressure are investigated in this paper. Time-averaged optical emission spectroscopy is used to measure the plasma parameters, of which the excitation electron temperature is determined by the Boltzmanns plot method whereas the gas temperature is estimated using a fiber thermometer. Furthermore, the Stark broadening of the hydrogen Balmer Hβ line is applied to measure the electron density, and the simultaneous presence of comparable Doppler, van der Waals, and instrumental broadenings is discussed. Besides, properties of the jet discharge are also studied by electrical diagnosis. It has been found that the electron densities in this argon plasma jet are on the order of 1014 cm−3, and the excitation temperature, gas temperature, and electron density increase with the applied voltage. On the other hand, these parameters are inversely proportional to the argon gas flow rate.

Inactivation of yeast by dielectric barrier discharge (DBD) plasma in helium at atmospheric pressure

To reveal the inactivation mechanism of microorganism in plasmas, a bakers yeast (Saccharomyces cerevisiae) sample is exposed in dielectric barrier discharge plasma in helium at atmospheric pressure. The mitochondrial activity charactering the survival probability of the yeast cell is measured by the 3-(4, 5-dimethylthiazol-2-yl) 2, 5-diphenyl-tetrazolium bromide method. The results show that the survival probability of yeast cells sharply decreases within the exposure time of 1.0-2.5 min and almost remains constant as exposure time is longer than 2.5min. The increase of the protein concentration in the supernatant solution of yeast suspension indicates that the intracellular proteins leak to the extracellular environment when the cells undergo plasma exposure, and gross structural damage is observed by a scanning electron microscope. The possible cause of the rupture is the electrostatic tension produced by the charges accumulated on the cell surface in the plasma. In addition, the extracellular medium whose pH is changed may also contribute to the rupture of the treated yeast cells.

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.

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.

Characteristics of nanosecond pulse needle-to-plane discharges at high pressure: a particle-in-cell Monte Carlo collision simulation

A model of one dimensional in position and three dimensional in velocity space self-consistent particle in cell with Monte Carlo collision technique was employed to simulate the argon discharge between the needle and plane electrodes at high pressure, in which a nanosecond rectangular pulse was applied to the needle electrode. The work focused on the investigation of the spatiotemporal evolution of the discharge versus the needle tip size and working gas pressure. The simulation results showed that the discharge occurred mainly in the region near the needle tip at atmospheric pressure, and that the small radius of the needle tip led to easy discharge. Reducing the gas pressure gave rise to a transition from a corona discharge to a glowlike discharge along the needle-to-plane direction. The microscopic mechanism for the transition can arguably be attributed to the peak of high-energy electrons occurring before the breakdown; the magnitude of the number of these electrons determined whether the breakdown can take place.

Optical and Electrical Diagnostics of Cold Ar Atmospheric Pressure Plasma Jet Generated With a Simple DBD Configuration

A cold Ar atmospheric pressure plasma jet generated using a DBD configuration device equipped with two powered electrodes as well as a grounded ring electrode driven by a sinusoidal excitation voltage at 38 kHz is presented in this paper. In this paper, properties of the jet discharge are studied by electrical diagnostics, including applied voltage, conducting current, and average absorbed power. Moreover, the optical emission spectroscopy is used to measure the plasma parameters, of which the electronic excitation temperature is determined by the Boltzmanns plot method using ten characteristic lines of Ar from 3p54p → 3p54s and 3p55p → 3p54s transitions whereas the gas temperature is obtained by using a fiber thermometer (FISO FOT-L-SD). It has been found that the conducting current, average absorbed power, the excitation temperature, and gas temperature increase with the applied voltage. On the other hand, these parameters are inversely proportional to the argon gas flow rate. What is more is that the production of oxygen radical (produced by the collisions between oxygen molecule from atmosphere and high-energy particles in plasma effluent) at a gas flow rate of 2 slm is investigated by means of optical actinometry, which is found to increase with the applied voltage.

Study on the Self-Organized Pattern in an Atmospheric Pressure Dielectric Barrier Discharge Plasma Jet

In this paper, a rich variety of self-organized patterns have been observed in a dielectric barrier discharge helium plasma jet generated at atmospheric pressure. It has been found that the evolvement of a discharge pattern in plasma jets is sensitive to diverse experimental parameters, including the applied voltage, the frequency of power, the scale of plasma jet generator, and the gas flow rate. By altering the applied voltage and/or the gas flow rate, the plasma jet is seen to evolve through three modes, which are diffuse-looking discharge, self-organized discharge with regular channels, and unstable discharge with random filaments. Among which, the self-organized discharge mode is characterized with several bright plasma channels stably formed in a straight line. The maximum number of channels is mainly determined by the scale of plasma jet generator. When the frequency is fixed, the minimum distance between two adjacent discharge channels in the self-organized mode is nearly the same, no matter what size tube is selected.