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We report in this Letter a kind of asymmetric discharge mode in positive and negative half-cycles of dielectric barrier discharge in ambient air. This phenomenon is characterized by homogeneous and filamentary discharges occurring alternately in the two half-cycles, using two different materials of alumina ceramic and quartz as the dielectric barrier at each side. The discharge current waveforms, discharge images, optical emission spectra, and the averaged electron energy are significantly different for the asymmetric discharges. It is suggested that the seed electrons and secondary electron emission from the different dielectric materials acting as the temporary cathode are responsible for the different discharge modes.

Formation and propagation of surface plasmons (SPs) of microwaves (MWs) along a dense non-uniform plasma column were investigated by employing the finite-difference time-domain method and evidenced by experiment of argon helicon plasma. The effects of plasma density, incident frequency, and radius of plasma column on the SP features were discussed. Results showed that when the MW frequency and the density distribution of plasma column satisfy suitable conditions, SPs can be excited on the surface of a uniform plasma column when the frequency is 2–5 times of the MW, while inside a nonuniform plasma column when the plasma frequency is only a little higher (about 5%–20%) than the MW. The SP wavelength depends on the plasma density for a given incident MW frequency. The forward scatter MW field will be enhanced significantly when SP appears along the nonuniform plasma column.

We present in this paper the comparison of an electric double layer (DL) in argon helicon plasma and magnetized direct current (DC) discharge plasma. DL in high-density argon helicon plasma of 13.56 MHz RF discharge was investigated experimentally by a floating electrostatic probe and local optical emission spectroscopy (LOES). The DL characteristics at different operating parameters, including RF power (300–1500 W), tube diameter (8–60 mm), and external magnetic field (0–300 G), were measured. For comparison, DL in magnetized plasma channel of a DC discharge under different conditions was also measured experimentally. The results show that in both cases, DL appears in a divergent magnetic field where the magnetic field gradient is the largest and when the plasma density is sufficiently high. DL strength (or potential drop of DL) increases with the magnetic field in two different structures. It is suggested that the electric DL should be a common phenomenon in dense plasma under a gradient external magnetic field. DL in magnetized plasmas can be controlled properly by magnetic field structure and discharge mode (hence the plasma density).

The striation phenomenon in large-gap coplanar plasma display panel (PDP) has been investigated experimentally in macroscopic cells. The results show that the striations can generate either above anode accompanying the development of discharge or in the weak-field plasma channel near the dielectric surface after the discharge having developed. The surface state of the dielectric layer and the pre-accumulated wall charge play non-important role on the generation of striation. It is supposed that the physical process in the gas volume govern the formation of striation in PDP cells.

In this paper, we present an experimental study on the self-pulsing phenomenon in a flow-induced atmospheric pressure plasma jet (APPJ) in a hollow electrode configuration driven by dc voltage supply. The current-voltage curve, the typical waveforms of current and voltage of self-pulsing, the time-resolved images, and the repetition frequency were measured under different experimental conditions. The results show that the APPJ of a hollow electrode can sustain in a stable, repeatable self-pulsing regime. The waveform of the pulsed current is very stable with nearly constant rising time and decay time at different discharge averaged currents. Although the pulsing frequency increases linearly with the averaged current and the gas flow rate, it decreases with the electrode gap. An equivalent electric circuit consisting of a capacitor and two resistors was used to model the self-pulsing discharge plasma. The simulation results and the time-resolved images recorded using an ICCD camera show that the pulsed pro...

Heterogeneous reaction is considered to be main mechanism in desulfurization from the flue gas by low temperature plasmas. The radical SO3 plays a major part in oxidizing sulfiteions to sulfate ions in reference to Huie's proposal. Solving the kinetic equationsreveals that the hydroxyl radicals absorbed in the liquid phase may contribute over 85% of desulfurization rate. which is over ten times of that due to gas phase reactions. The predicted area factor effect is proved by the experiments.

Our investigations on corona induced non-thermal plasmas include both fundamental study and products development. This paper presents our recent work in following subjects: investigation on characteristics of pulsed corona discharge in relation with flue gas cleaning; evaluation of high voltage power supply; design of plasma reactor; experimental study on DeNOx and DeSO2; decomposition of VOCs and indoor air cleaning.

This paper demonstrates that the main reaction mechanism of flue gas desulfurization (FGD) by pulsed corona discharge or electron beam, which generates non-thermal plasmas (NTP), is heterogeneous. The experimental results in this paper suggest that the main reactions in FGD by NTP are activated reactions in liquid phase. According to Huie’s mechanism, it is considered that the ionic radical SO - 3 plays a major part in oxidizing sulfite ions to sulfate ions. Kinetic analysis proves the existence of prior equilibrium and hints that improvement of absorption of gas radicals may promote performance. Solving the kinetic equations with a suggested effective area factor φ reveals that the hydroxyl radicals absorbed in the liquid phase may contribute to over 80% of the overall desulfurization rate. Both theoretical and experimental correlations between desulfurization rate, energy yield and the operating parameters have been obtained, showing satisfactory agreement with each other.

The contribution of electric quadrupole (E2) transitions to the opacity of hot and dense plasmas is taken into account by using an average-atom model. As an example, the increase of the opacity of Au due to the E2 transition is shown to range from less than 1% to more than 10% depending on density and temperature. It reaches 15% when the density and temperature are, respectively, 100 g/cm(3) and 5000 eV. The most significant influence comes from the E2 photoionization processes.

Minimum ignition energy is one of the important characteristics for electrostatic sensitivity of explosives and determination of the spark discharge energy is necessary for decision making of explosion prevention. In this paper, the real spark discharge energy was determined by the integration of the measured voltage and discharge current in a needle-to-plate configuration. The influence of the charging voltage and polarity, the charging capacitance and the electrode gap on the spark discharge energy was investigated. It is shown that the energy deposited into the discharge system is always smaller than that stored in the charging capacitor, especially at lower voltages that the discharge shows one current pulse and the energy efficiency is less than 30%. The discharge becomes complete at higher voltages when the discharge shows double pulses and the energy efficiency is close to 100%. For given charging capacitance and voltage, the real discharge energy is determined by the discharge mode rather than the electrode gap or the voltage polarity.

In this paper, the numerical study has been performed on the xenon positive column discharges of mercury-free fluorescent lamp. The plasma discharge characteristics are analyzed by numerical simulation based on two-dimensional fluid model. The effects of cell geometry, such as the dielectric layer, the electrode width, the electrode gap, and the cell height, and the filling gas including the pressure and the xenon percentage are investigated in terms of discharge current and discharge efficiency. The results show that a long transient positive column will form in the xenon lamp when applying ac sinusoidal power and the lamp can operate in a large range of voltage and frequency. The front dielectric layer of the cell plays an important role in the xenon lamp while the back layer has little effect. The ratio of electrode gap to cell height should be large to achieve a long positive column xenon lamp and higher efficiency. Increase of pressure or xenon concentration results in an increase of discharge efficiency and voltage. The discussions will be helpful for the design of commercial xenon lamp cells.