Yelin Hu

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.

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...

Slot-array antenna devising for surface microwave discharge of surface plasmon polaritons

The production of surface microwave discharge is verified as a stable discharge excited by surface electromagnetic waves which is carried by surface plasmon polaritons. In order to achieve the purpose of coupling microwave energy efficiently and surface-wave discharge stably, in addition based on the dipole near-field radiation theory, we design the subwavelength diffraction grating. Moreover, the near-field radiation electric field distribution is studied by special proposed computation method and further the aim of design is achieved.

Donut shape plasma jet plumes generated by microwave pulses even without air mole fractions

It is well known that the plasma jets driven by lower frequency voltages or pulsed DC power supply normally present with donut shaped cross sections, especially at where the diffused air mole fractions are less than 0.01. Thence, it is interesting to further study whether the donut shape is still in truth for the pulsed microwave plasma jet or not. In this letter, the cross sectional structures of atmospheric pressure plasma jet plumes driven by pulsed microwaves have been experimented on a cylindrical coaxial transmission line resonator. The plasma jet plumes demonstrate particular characteristics, like argon plasma with a donut shape but helium plasma with an uniform lighten cross section, despite whether the air mole fraction exists or not. For argon discharge, the fast images show that the donut shaped cross section only occurs at the end of each microwave pulses. In combination with helium discharge, the cross sectional patterns are immediately determined by the dominant ionization front of the plasm...

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.