Guangqing Xia

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.

PIC/MCC Simulation of the Ionization Process for Filamentary Streamer Plasma Jet at Atmosphere Pressure in Argon

Recently, we have reported a microwave plasma jet at atmosphere in argon, capable of generating filamentary streamer discharges within the entire quartz tube, while several bifurcations yield at the end of the copper wire immediately in the quartz tube when incident power reaches 20 W. However, the ionization process for the discharges is still not very well clarified. This paper shows a numerical study of the proposed plasma jet by means of the 2D3V particle in cell with Monte Carlo collision method. The detailed information about the distributions of plasmas and electromagnetic fields is obtained by sampling the simulated results at different time steps. The simulation results suggest that the production of the proposed plasma jet is attributed to the seed plasmas triggered by the enhanced electric field of surface plasmon polaritons and its interaction with plasmas.

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...

Longer Microwave Plasma Jet With Different Discharge Performances Originated by Plasma–Surface Interactions

With an input power of 50 W and a gas pressure of 100 Pa, 2.5 (without metal wire) and 10.5 cm (with a copper wire) long microwave air plasma jets are generated, respectively. When 95% Ar + 5% O2 is instead of air, the length of the plasma jet is stretched to 15 cm. Furthermore, the length of plasma plume is affected differently by adding the processed materials. These different discharge performances originate from the effect of plasma-surface interactions.

Study on hairpin-shaped argon plasma jets resonantly excited by microwave pulses at atmospheric pressure

In the present study, atmospheric pressure argon plasma jets driven by lower-power pulsed microwaves have been proposed with a type of hairpin resonator. The plasma jet plume demonstrates distinctive characteristics, like arched plasma pattern and local plasma bullets. In order to understand how the hairpin resonator works, electromagnetic simulation of the electric field distribution and self-consistent fluid simulation of the interaction between the enhanced electric field and the pulse plasma plume are studied. Simulated spatio-temporal distributions of the electric field, the electron temperature, the electron density, and the absorbed power density have been sampled, respectively. The experimental and simulated results together suggest that the driving mechanism of the hairpin resonator works in the multiple electromagnetic modes of transmission line and microwave resonator, while the local plasma bullets are resonantly generated by local enhanced electric field of surface plasmon polaritons. Moreove...

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.

Bullet-shaped ionization front of plasma jet plumes driven by microwave pulses at atmospheric gas pressure

Ionization waves (propagating bullet-shaped plasma) are always present in atmospheric-pressure plasma jets generated by a pulsed DC power supply or low-frequency voltages. Nevertheless, whether these ionization waves exist for pulsed microwave plasma jets remains unclear. In this paper, a coaxial transmission line resonator driven by microwave pulses is capable of generating atmospheric pressure plasma jet plumes. Depending on the discharges, these plasma jet plumes exhibit distinctive characteristics, such as bullet-shaped ionization fronts for argon plasma and ball-shaped for helium plasma. Fast images show argon plasma plumes generating several small branches but only one dominant ionization front travels more distance along the jet axis. Both ionization-wave images and electromagnetic simulation results indicate that the bullet-shaped ionization front forms a plasma jet plume immediately. The dominant ionization wave is resonantly excited by the local enhanced electric field, which originates from the...

The quenching effect of hydrogen on the nitrogen in metastable state in atmospheric-pressure N2-H2 microwave plasma torch

The atmospheric-pressure microwave N2-H2 plasma torch is generated and diagnosed by optical emission spectroscopy. It is found that a large amount of N atoms and NH radicals are generated in the plasma torch and the emission intensity of N2+ first negative band is the strongest over the spectra. The mixture of hydrogen in nitrogen plasma torch causes the morphology of the plasma discharge to change with appearance that the afterglow shrinks greatly and the emission intensity of N2+ first negative band decreases with more hydrogen mixed into nitrogen plasma. In atmospheric-pressure microwave-induced plasma torch, the hydrogen imposes a great influence on the characteristics of nitrogen plasma through the quenching effect of the hydrogen on the metastable state of N2.

Role of Discharge Tube in Determination of Operating Mode in Waveguide-Based Atmospheric-Pressure Microwave-Induced Plasma

The discharge mechanism of the atmospheric-pressure waveguide-based microwave plasma is investigated experimentally by considering the role of the discharge tube. When the radius of the aperture holes on the wide waveguide walls is equal to that of the thin-walled discharge tube, the plasma is induced in an equivalent resonator with a certain Q value, presenting a torch-like plasma. However, if there is a launching gap of enough interspace between the aperture holes and the discharge tube, a surfaguide plasma can be developed at atmospheric pressure.

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.