Radio-frequency Atmospheric-pressure Glow Research Articles

Electrical and optical characteristics of radio-frequency atmospheric dielectric barrier discharge using anodic alumina barriers

It is widely accepted that dielectrically insulated electrodes can control plasma contraction in radio frequency atmospheric pressure glow discharge at very large currents. It is also known that thin dielectric barriers maximize the permissible discharge current, thus boosting the reactive plasma species and enhancing the application efficacy. An experimental investigation of radio-frequency atmospheric pressure dielectric barrier discharge (rf APDBD) using a thin layer of a novel dielectric, anodic alumina grown by a wet electrochemical process to insulate electrodes is presented in this paper to demonstrate that rf APDBD with anodic alumina barriers remains stable and retains volume without contraction over a wide current range in the γ-mode. The electrical characterization of the rf APDBD is performed using an equivalent electric circuit model based on the measured electrical parameters. In normal glow discharge, the measured impedance data closely matched the simulated data. Optical emission spectroscopy demonstrated that a higher discharge current facilitated active plasma chemistry. The estimated excitation, vibrational, and gas temperatures indicate that rf APDBD with anodized electrodes is well suited for surface treatment and decontamination applications in open air.

Enhancement of Radio Frequency Plasma Plume by Pulsed Plasma Bullet at Atmospheric Pressure

An experimental study of a plasma plume generated by radio frequency atmospheric pressure glow discharge and enhanced in terms of plume length and intensity by pulsed discharge is presented. When injecting a pulsed plasma bullet into the radio frequency plasma plume, the length of the plasma plume into ambient air can be elongated from 2 mm to 6 mm and the intensity of the plasma plume can be elevated by four times. The propagation of the pulsed plasma bullet and the interaction with radio frequency discharge and plume are demonstrated by the temporal evolution of the discharge spatial appearance. The enhanced plasma plume is employed to improve the O/C ratio of carbon fiber, which is attributed to the synergistic effect of the radio frequency plasma plume and pulsed plasma bullet.

The double coupled microwave resonance probes and application for diagnosing atmospheric pressure plasma jet

The double-coupled microwave resonance probe (DMRP) based on the hairpin probe is proposed for diagnosing atmospheric plasma jet (). In this work, the resonance characteristics of DMRP are investigated by numerical simulation. It shows that two resonance peaks on the reflectance spectrum can be observed, and influenced significantly by some parameters, such as the probe separation, the distance to the handheld radio frequency atmospheric pressure glow discharge plasma jet (RF-APGDPJ) and the plasma electron density less than 1017 m−3. Based on two resonance modes of DMRP, the electron densities in the afterglow of RF-APGDPJ at the different rf powers and helium flow rates are diagnosed experimentally by matching the change of FWHM ( and ) measured by vector network analyzer with the simulated relation between the FWHM changes and the plasma density.

Injection of plasma plume into radio frequency atmospheric pressure glow discharge

The influence of a high voltage sub-microsecond pulsed plasma plume on a radio frequency discharge at atmospheric pressure is studied experimentally. The discharge characteristics and dynamics of pulsed discharge and radio frequency discharge are characterized in terms of voltage and current waveforms and spatio-temporal evolution of discharge. It is found that the plasma bullet generated by pulsed discharge can inject into the radio frequency discharge region with the average travelling speed of 70 km/s. The radio frequency discharge intensity is elevated to be 3 times higher as the plasma bullet penetrating the interelectrode gap of radio frequency discharge. The enhancement is attributed to the injection of energetic electrons by the plasma bullet, which is demonstrated by the temporal evolution of discharge image intensity and optical emission spectroscopy intensity.

Contrasting Characteristics of Radio-Frequency Atmospheric Argon Discharges With and Without Dielectric Barriers

In this paper, the fundamental characteristics of glow discharge operation modes in radio frequency (RF) atmospheric argon discharges with and without dielectric barriers were studied by experiments. It is found that the RF dielectric-barrier discharge (DBD) in atmospheric argon operates more stable in alpha mode than RF atmospheric pressure glow discharge in argon. The ratios of oxygen and nitrogen to argon are achieved to be 9.5% and 6% in stable RF DBD in atmospheric argon, respectively. The plasmas chemistry, measured by optical emission spectra and intensity, explains that the stable alpha mode discharge range is larger with mixture of oxygen than nitrogen.

Studies on gas breakdown in pulsed radio frequency atmospheric pressure glow discharges

In pulsed RF atmospheric pressure glow discharges, the gas breakdown judged by the rapid drop in the amplitude of the pulsed RF voltage is no longer universally true. The steep increment of the plasma-absorbed RF power is proposed to determine the gas breakdown. The averaged plasma-absorbed RF power over a pulse period is used to evaluate effects of the preceding pulsed RF discharge on the breakdown voltage of the following one, finding that the breakdown voltage decreases with the increment in the averaged plasma-absorbed RF power under constant pulse duty ratio. Effects of the pulse off-time on the breakdown voltage and the breakdown delay time are also studied. The obtained dependence of the breakdown voltage on the pulse off-time is indicative of the transitional plasma diffusion processes in the afterglow. The breakdown voltage varies rapidly as the plasma diffuses fast in the region of moderate pulse off-time. The contribution of nitrogen atom recombination at the alumina surface is demonstrated in the prolonged memory effect on the breakdown delay time vs. the pulse off-time and experimentally validated by introducing a trace amount of nitrogen into argon at short and long pulse off-times.

Radio frequency atmospheric pressure glow discharge in α and γ modes between two coaxial electrodes

The discharge in pure helium and the influence of small nitrogen impurities at atmospheric pressure are investigated based on a one-dimensional self-consistent fluid model controlled by a dielectric barrier between two coaxial electrodes. The simulation of the radiofrequency (rf) discharge is based on the one-dimensional continuity equations for electrons, ions, metastable atoms, and molecules, with the much simpler current conservation law replacing the Poisson equation for electric field. Through a computational study of rf atmospheric glow discharges over a wide range of current density, this paper presents evidence of at least two glow discharge modes, namely the α mode and the γ mode. The simulation results show the asymmetry of the discharge set exercises great influence on the discharge mechanisms compared to that with parallel-plane electrodes. It is shown that the particle densities are not uniform in the discharge region but increase gradually from the outer to the inner electrode in both modes. The contrasting dynamic behaviors of the two glow modes are studied. Secondary electron emission strongly influences gas ionization in the γ mode yet matters little in the α mode.

Three modes in a radio frequency atmospheric pressure glow discharge

Fundamentally not requiring a vacuum chamber, atmospheric pressure glow discharges (APGDs) offer an exciting prospect for a wide range of material processing applications. To characterize their operation and establish their operation range, a radio frequency (rf) APGD is studied experimentally with measurement of discharge voltage, current, dissipated plasma power and plasma impedance. Different from the current understanding that rf APGD are operative only in the abnormal glow mode, we show the presence of two additional modes namely the normal glow mode and the recovery mode. It is shown that all three modes are spatially uniform and possess key characteristics of a glow discharge. So rf APGD have a much wider operation range than previously believed. To provide further insights, we investigate the transition from the abnormal glow mode to the recovery mode. It is established that the cause responsible for the mode transition is sheath breakdown, a phenomenon that is known in low- and moderate-pressure glow discharges but has not been reported before for atmospheric-pressure glow discharges. Finally we demonstrate that plasma dynamics, hence plasma stability, in these three modes are influenced crucially by the impedance matching between the plasma rig and the power source.