Lingli Hong

Filamentary streamer discharges in argon at atmospheric pressure excited by surface plasmon polaritons.

This paper describes a microwave plasma jet in an argon atmosphere capable of generating filamentary streamer discharges within the entire quartz tube excited by surface waves of surface plasmon polaritons (SPPs) located in the tube. Several discharge streamers are immediately produced at the end of the copper wire when incident power reaches 20 W. From simulations, the wavelength of the surface wave was found to be approximately 5.7 cm. Although the developing streamers induce E-field enhancements favoring discharging, more streamer bifurcations requiring additional energy to maintain discharging diminish the resonant enhanced E-field. The underlying mechanism of the proposed plasma jet is resonant excitation of SPPs and its interaction with plasmas.

Self-consistent fluid modeling and simulation on a pulsed microwave atmospheric-pressure argon plasma jet

In present study, a pulsed lower-power microwave-driven atmospheric-pressure argon plasma jet has been introduced with the type of coaxial transmission line resonator. The plasma jet plume is with room air temperature, even can be directly touched by human body without any hot harm. In order to study ionization process of the proposed plasma jet, a self-consistent hybrid fluid model is constructed in which Maxwells equations are solved numerically by finite-difference time-domain method and a fluid model is used to study the characteristics of argon plasma evolution. With a Guass type input power function, the spatio-temporal distributions of the electron density, the electron temperature, the electric field, and the absorbed power density have been simulated, respectively. The simulation results suggest that the peak values of the electron temperature and the electric field are synchronous with the input pulsed microwave power but the maximum quantities of the electron density and the absorbed power density are lagged to the microwave power excitation. In addition, the pulsed plasma jet excited by the local enhanced electric field of surface plasmon polaritons should be the discharge mechanism of the proposed plasma jet.

Effect of wave-mode conversion device on production of large-area rectangular overdense surface-wave plasmas at the gas pressure about 100 Pa

In this paper, the wave-mode conversion devices with three different structures have been devised for plasma heating. Surface-wave plasma (SWP) discharge analysis with or without considering the collision loss is presented theoretically. The comparative discharge experiments have been operated for obtaining the uniform stable microwave discharges. When a specially designed microwave appliance is selected as the proposed wave-mode conversion device, the discharges driven by resonant excitation with surface wave (SW) have yielded plasmas with density of about 1018 m−3 at the gas pressure larger than 10 Pa. By comparing the results, the production of large-area uniform stable overdense SWP is attributed to the resonant excitation with SW evenly on the whole dielectric-plasma interface by the application of the specially designed wave-mode conversion device.

Particle-in-cell/Monte Carlo collision simulation of the ionization process of surface-wave plasma discharges resonantly excited by surface plasmon polaritons

Although surface-wave plasma (SWP) sources have many industrial applications, the ionization process for SWP discharges is not yet well understood. The resonant excitation of surface plasmon polaritons (SPPs) has recently been proposed to produce SWP efficiently, and this work presents a numerical study of the mechanism to produce SWP sources. Specifically, SWP resonantly excited by SPPs at low pressure (0.25 Torr) are modeled using a two-dimensional in the working space and three-dimensional in the velocity space particle-in-cell with the Monte Carlo collision method. Simulation results are sampled at different time steps, in which the detailed information about the distribution of electrons and electromagnetic fields is obtained. Results show that the mode conversion between surface waves of SPPs and electron plasma waves (EPWs) occurs efficiently at the location where the plasma density is higher than 3.57 × 1017 m−3. Due to the effect of the locally enhanced electric field of SPPs, the mode conversion...

Production of 30-mm Wide DC-Driven Brush-Shaped Cold Plasmas and Simulation on Its Discharge Process

In this paper, cold atmospheric pressure brush-shaped plasmas are reported. The brush, which is driven by a direct current (dc) power supply, is capable of generating plasmas glow up to 30-mm wide with no gas flow supplement. The plasmas can be touched by bare hand without any feeling of electrical shock or warmth. Current measurements show that the discharge in air appears periodically pulsed, while the discharge in argon actually presents either pulsed, except for their discharge mechanism placed at differently. For understanding this particular characteristic, a 2-D fluid model is developed with the use of Comsol Multiphysics software, under the condition of discharge in argon treated as an example. The simulation results are in good agreement with our discharge experiment in argon, which further indicate that the space charges trapped along the whole dielectric surface in air but only confined in the hole ahead the anode needle tip in argon may be responsible for the generation of the different pulsed discharges.

Study on DC-Driven Air Cold Plasma Brushes Generated Without Airflow Supplement

In this paper, 30-mm-wide cold atmospheric-pressure air plasma brushes are reported. The brushes driven by a direct current power supply are capable of generating air plasma glows with no noble gas addition and no airflow supplement. There is no risk of glow-to-arc transitions, and the plasma glow appears uniform no matter what kinds of material are being processed. The air plasma glow can be scaled up by using the plasma brush arrays. About 30mm × 30mm × 5mm (W, H, and L) homogeneous air plasma glow is generated by merging seven-brush arrays. Current measurements show that the single-brush discharge appears periodically pulsed, while the brush array discharge actually presents either pulsed with about array-number-times frequency of the single one. A further analysis indicates that the charge particles trapped along the dielectric surface may be responsible for the discharges.

Correction to “Production of 30-mm Wide DC-Driven Brush-Shaped Cold Plasmas and Simulation on its Discharge Process” [Jun 13 1658-1663]

In the above-named work, the affiliation of the first author is incorrect. It is corrected herein.

Theoretical analysis of surface microwave discharge resonantly excited by surface plasmon polaritons

The generation mechanism of surface microwave discharge is studied by analyzing the simplified surface-wave plasma model, from which we show the spatial distribution characteristics of the surface electromagnetic waves. According to the characteristics of overdense plasma interacting with high-frequency electromagnetic waves, we get there is the surface plasmon polaritons (SPPs) phenomenon placed at the interface between overdense plasmas and dielectric. The characteristic parameters of SPPs in overdense plasmas are obtained by altering the plasma density and the collision frequency.

Determination of the local electron density based on millimeter wave interferometry II: Experimental operations and comparisons

The determination method of the local electron density is shown based on millimeter wave interferometry and the electron density measuring is experimented on a cylindrical capacitively coupled plasmas (CCP) setup. Results show the excellent agreement between the radial density profiles in the central plane measured by interferometry with the proposed analysis method and by the Langmuir probe system.

Determination of the local electron density based on millimeter wave interferometry I: Theoretical analysis

The determination method of the local electron density is analyzed based on millimeter wave interferometry and the electron density measuring is experimented on a cylindrical plasmas setup. Analyses show that the local electron density is obtained with better precision by using the proposed method than that by adopting the traditional line-average method. Moreover, this method can also be exploited to determine the electron density and its spatial distribution accurately for other plasma sources.