Qiu-Yue Nie

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.

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.

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.

A cold atmospheric pressure plasma jet controlled with spatially separated dual-frequency excitations

A dual-frequency cold atmospheric pressure plasma (CAP) jet is studied as a possible route to separate control of basic plasma parameters particularly plasma density, plasma plume length and gas temperature. With spatially separate application of two excitation frequencies, one at 5.5 MHz and the other at 30 kHz, plasma dynamics exhibit interaction between influences by the two individual excitation frequencies. However, this interaction is well controlled as manifested in the voltage dependence of plasma density and gas temperature. The dual-frequency CAP jet is shown to increase its optical emission intensity by at least three times, but without much increase in its gas temperature, compared with the maximum emission intensity of its single-frequency counterparts. Its plume length is also longer, realized at the applied voltages well below the minimum value necessary for single-frequency jets to form. It is shown that the upperstream discharge at 5.5 MHz feeds abundant electrons to the downstream plasma plume sustained at 30 kHz for the latter to acquire high plasma density and long plume length. Dual-frequency cold atmospheric pressure plasma jets offer a step change in capability, characters and possibly underpinning physics from their single-frequency counterparts.

Array of surface-confined glow discharges in atmospheric pressure helium: Modes and dynamics

Array of atmospheric pressure surface discharges confined by a two-dimensional hexagon electrode mesh is studied for its discharge modes and temporal evolution so as to a theoretical underpinning to their growing applications in medicine, aerodynamic control, and environmental remediation. Helium plasma surface-confined by one hexagon-shaped rim electrode is shown to evolve from a Townsend mode to a normal and abnormal glow mode, and its evolution develops from the rim electrodes as six individual microdischarges merging in the middle of the hexagon mesh element. Within one hexagon element, microdischarges remain largely static with the mesh electrode being the instantaneous cathode, but move towards the hexagon center when the electrode is the instantaneous anode. On the entire array electrode surface, plasma ignition is found to beat an unspecific hexagon element and then spreads to ignite surrounding hexagon elements. The spreading of microdischarges is in the form of an expanding circle at a speed of ...

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.

Characteristics of Atmospheric Room-Temperature Argon Plasma Streams Produced Using a Dielectric Barrier Discharge Generator With a Cylindrical Screwlike Inner Electrode

In this paper, an innovative coaxial-type dielectric barrier discharge plasma generator is proposed to produce the large-volume and visibly uniform cold argon plasmas at atmospheric pressure by enhancing the local intensity and uniformity of the electric field simultaneously with the aid of a cylindrical screwlike inner electrode configuration. The experimental measurements show that the discharges transit from the initial stage after breakdown to the stable stage through a transitional stage and finally reach an unstable discharge stage with the increase of the applied voltage. The estimated values of the electron temperature and the number density of the gas discharge plasmas in the electrode region vary in a small range, i.e., 8.0-8.9 eV and (4.6-6.4) × 1011 cm-3, with increasing the applied voltage. Moreover, the plasma streams are quite uniform in the radial direction with a low gas temperature ( ~ 300 K) and an abundance of chemically reactive species in the stable discharge stage, which will be potentially a useful tool for the treatment of the heat-sensitive materials.

Investigations on an Atmospheric Dielectric Barrier Discharge Plasma Jet With a Concentric Wire-Mesh Cylinder Electrode Configuration

An atmospheric-pressure plasma jet generated by a sinusoidal power input of tens of kilohertz and designed with a concentric wire-mesh cylinder electrode is characterized in this paper. Effects of gas flow rate on the length of plasma jet have been investigated, and the plasma jet is seen to have three different modes varied with the gas flow. The jet temperature is measured by fine-structure fitting of the emission bands of UV OH, molecules, and the Boltzmann plot method, and in comparison with the data obtained by an optical-fiber thermometer. In addition, the electron density in the generation region is diagnosed by stark broadening. Plasma bullet properties such as velocity, luminosity, their time of formation and extinguishment, and traveling distance are studied with variation of the applied voltage, gas flow rate, and operating frequency of power supply. Notably, the bullet velocity is found to have decreased with the applied voltage but increased with the operating frequency. Furthermore, the maximum velocity is reached earlier for lower gas flow rates and higher applied voltages, but its value is independent of the gas flow rate.