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Atmospheric-pressure dielectric barrier discharge (DBD) with airflow participation has been widely used in recent years. In this experimental study, a diffuse DBD excited by repetitive nanosecond pulses is achieved in airflow. Upon the introduction of airflow to the gas gap, the discharge state transforms from a filamentary one into a diffuse one at first, followed by the generation of a thin filamentary discharge (TFD) at a high airflow rate. It is observed that the diffuse discharge (DD) and the TFD are ignited from the electrode boundary, which subsequently move toward the downstream region with a velocity below the corresponding airflow rate. Subsequent to hundreds of pulse cycles, a stationary discharge state is formed with the TFD in the upstream region and the DD in the downstream region. The length of the TFD region is associated with the airflow rate, the pulse repetition frequency (PRF), and the applied voltage. The observations presented above are ascribed to the transverse electric field at the electrode boundary and the redistribution of charges under the action of airflow.

Many studies have demonstrated the utility of surface dielectric barrier discharge (SDBD) plasma actuators driven by different voltage waveforms for airflow control. In this paper, a new dual-power supply voltage consisting of ac high voltage with a superimposed positive or negative pulse bias voltage is applied to a two-electrode structure SDBD actuator to compare the actuator performance with that driven by a single ac voltage waveform. The ionic wind velocity, the thrust force, and the schlieren visualization images are studied under three types of voltage waveforms: single ac voltage, ac voltage superimposed with a positive pulse bias voltage (ACPP), and ac voltage superimposed with a negative pulse bias voltage (ACNP). The influences of different pulse parameters including pulse voltage, pulse repetition frequency (PRF), and pulsewidth on the actuator performance are studied in detail. Experimental results show that pulse voltage and PRF have more notable influence on the actuator performance when the actuator is driven by ACPP, while the pulsewidth has little effect on the actuator performance. In contrast, the actuator performance is little changed when the actuator is driven by ACNP. The positive and negative pulse discharges have different effects on the actuator performance, the reason is positive pulse discharge increases the discharge of glow-like region while negative pulse discharge increases the discharge of streamer region in the following ac cycle. The schlieren images further indicate pulse discharge exerts its effects on the SDBD actuator performance by affecting the electric field of ac discharge.

A tubular plasma source was developed to generate high-density plasma beam for nitriding using N2 + H2 mixture as working gas. The plasma source was demonstrated to be capable of generating a plasma plume with density of N2+ as high as ~ 7.2 ± 0.6 × 1011 cm− 3 in N2 + H2 mixed gases with N2 content changed from 92.5% to 32.5%. After nitriding at 450 °C for 120 min, ~ 5-μm thick compound layers formed on the sample surface of pure iron with diffusion zone as deep as 0.4 mm, leading to 7.5– 8.5 GPa hardness. In addition, nitriding of pure iron could be realized at a low temperature as low as 250 °C, producing a compound layer with a thickness of ~ 2.5 μm. After nitriding for 120 min at temperatures of 330– 500 °C, the high-density plasma flow could produce a compound layer of 4– 5 μm with hardness of 10 GPa. N2+ and N+ are suggested to be responsible for the nitriding of pure iron by the high-density plasma beam. The tubular plasma source allows us using N2 + H2 mixed gas with low hydrogen content for high-efficient nitriding. The gas temperature in plasma plume is ~ 300 °C, and thus is acceptable for low-temperature nitriding.

The surface dielectric barrier discharge (SDBD) plasma actuator has shown great promise as an aerodynamic flow control device. In this paper, the encapsulated electrode width of a SDBD actuator is changed to study the airflow acceleration behavior. The effects of encapsulated electrode width on the actuator performance are experimentally investigated by measuring the dielectric layer surface potential, time-averaged ionic wind velocity and thrust force. Experimental results show that the airflow velocity and thrust force increase with the encapsulated electrode width. The results can be attributed to the distinct plasma distribution at different encapsulated electrode widths.

The temporally and spatially resolved optical emission spectrum of Hα of a pulsed spark discharge in water was experimentally measured. The temporally and spatially resolved electron densities, along the radial direction of the spark filament, for a pulsed spark discharge in water with a conductivity of 100 μS/cm were investigated. The electron density in the spark filament was found to be in the 1018/cm3 order of magnitude. The highest electron density was measured at the primary stage of the spark filament, and it decreased with time. The radial distribution of electron density increased from the center to the edge of the spark filament.

We report a tubular plasma source that is capable of creating high-activity nitrogen plasma flow at low pressure. The high-activity nitrogen plasma was produced by a continue low-frequency discharge, in which an intensive pulsed discharge was observed when the electrode was polarized by the positive voltage. Excited at 10 to 115 W, the plasma source allows loading the power density as high as ~ 80 W/cm3 to the plasma, producing high-activity nitrogen plasma with a maximum dissociation degree of nitrogen larger than 10%. Based on the tubular plasma source, a special system of plasma enhanced chemical vapor deposition has been developed for deposition of low H-content amorphous hydrogenated silicon nitride (a-SiNx:H) films at room temperature.

The dynamics of plasma and ejection characteristics of spheromaks produced by a magnetized coaxial plasma gun are studied. By placing three magnetic probes at various axial positions, the distribution of current paths in the gun is found to vary in two distinct discharge modes. During the first half-period of a discharge, the plasma moves forward in the form of a current sheet, while the diffuse distribution of current paths in the second half-period indicates a deflagration mode. The evolution images and photodiode signals of the plasma show that only a single spheromak is ejected during the entire discharge. This is because the diffuse current paths reduce the J × B Lorentz force on the leading-edge plasma, which cannot be ejected from the gun. In addition, the existence of kinks in the plasma flow in two discharge modes proves that the instability is driven by E r × B z drift, which causes rotation of the central column. Spheromak velocities increase linearly with discharge current amplitude but are inversely proportional to the gas puff mass. In ejected spheromaks, both toroidal and poloidal magnetic fields are axisymmetric, with field strength increasing with discharge current. During magnetic reconnection events, the toroidal electric field V z × B r drives toroidal current that generates an additional poloidal field that amplifies the starting magnetic field in the spheromak plasma. This study clarifies the relationship between the formation of a single spheromak and the current distribution, and also provides a new way to optimize the spheromak's injection performance.

In this paper, plasma kinetics of CH4/O2 at atmospheric pressure are of interest for applications in plasma chemistry where partial oxidation of methane to oxygenates and syngas are investigated by zero-dimensional global model. Effect of methane mole fraction ranging from 5% to 99% on plasma kinetics is studied in detail.It is found that electron density and electron temperature change periodically with periodic variation of power density pulse. The number densities of free radicals, ions and stable molecules are discussed as a function of simulation time and CH4/O2 molar ratio. Conversions of inlet gases, selectivities and yields of important products, and optimum methane content for methanol and formaldehyde formation are calculated and presented. In addition, CH3 radical is found to be the key intermediate for oxygenates production by analyzing the underlying dominant reaction pathways. Finally, a schematic overview of the transformation relationship between dominant plasma species is also summarized and shown

The aspect ratio (AR) of discharge geometry is an important parameter in view of inductively coupled plasma (ICP) source design. AR is defined as the ratio of chamber radius (R) and chamber height (L). The effects of the AR on plasma parameters and uniformity are investigated in a 2 MHz ICP source. The argon discharge is performed in two chambers of AR = 0.72 and 0.35 with different heights, and the effects of AR on electron loss mechanisms are studied using a global model. The results show a tendency for generation of higher density plasma with better uniformity in the case of AR = 0.72 at 0.5–2 Pa. The difference in electron density is caused by the differences in the volume. The observations on plasma uniformity are explained by the study of the electron loss mechanism. The accumulation of electrons is weakened by axial diffusion at the chamber center in the case of AR = 0.72. The difference in plasma uniformity between the two chambers diminishes with the increase in the gas pressure from 0.5 to 2 Pa, which results from the fact that the electron diffusion along the axial direction becomes more difficult. At higher pressures from 5–10 Pa, the ambipolar diffusion loss of electrons to the chamber wall becomes more difficult with the increase in pressure due to frequent collisions. Therefore, the electron accumulation in the discharge center is more evident in the chamber with AR = 0.72, which deteriorates the plasma uniformity. The above study can give a reference to the design of cylindrical ICP sources for practical applications.

The effect of flowing air on dielectric barrier discharge excited by alternating voltage was investigated by high-speed video analysis and electrical measurements. The discharge was still in filamentary mode in flowing air, and the space-time distribution of filaments was changed by airflow. With the increase in airflow velocity, the space-time distribution of discharge filaments shown in top view images went through four phases, that is, spot-like distribution, line-like distribution, cotton-like distribution, and stripe-like distribution. Accordingly, the motion and morphology of discharge filaments shown in side view images also presented four phases: remaining still and straight between adjacent cycles, moving and bending downstream, almost remaining still and straight between adjacent cycles, and moving and bending downstream again. Different motions of filaments were considered to be the reason for the changed distribution of filaments in flowing air. In addition, the intensity of discharge in flowing air was enhanced by increasing the gas gap and discharge frequency. At high discharge current, larger airflow velocity was needed to reach phase transition. The changed distribution of micro-discharge remnants in flowing air can be responsible for the phase transition. Micro-discharge remnants redistributed during the time interval of adjacent half-cycle discharges, under the action of various forces, such as electric field force, drag force, repulsive force, electrostatic coupling force, and trap binding force. The changed position of micro-discharge remnants led to the complex motions of discharge filaments and further resulted in the changed space-time distribution of filaments.

Dielectric barrier discharge in air at atmospheric pressure is produced using nanosecond pulsed supply. The effects of airflows on the discharge characteristics, such as discharge current, breakdown voltage, discharge uniformity, and luminous intensity, are investigated at different discharge gaps and pulse repetitive rates. The peak value of the primary discharge current is increased and the luminous intensity is decreased when the airflow rate increases from 0 to 10 m/s at any discharge gap and pulse repetitive frequency. At 1200-Hz pulse repetitive rate, the discharge becomes more uniform at the bigger discharge gap and the breakdown voltage increases when airflow is introduced into the discharge gap. However, at 100-Hz pulse repetitive rate, the discharge uniformity does not change and breakdown voltage decreases when airflow is introduced into the discharge gap. The experimental results also show that the discharge characteristics have significant changes with the airflow rate increasing from 0 to 10 m/s, while almost no obvious change is observed with the airflow rate increasing from 10 to 30 m/s.

In this study, an atmospheric-pressure He/O2 or Ar/O2 plasma jet is generated by a specially designed equipment with two coaxial quartz tubes and double power electrodes to remove lubricants from the surfaces of metals. The experimental results indicate that the cleaning performance is much better in the Ar/O2 plasma jet than in the He/O2 plasma jet under the same input power and O2 mixing ratio. It is found that more electron, more atomic oxygen, and more metastable Ar atoms generated in the Ar/O2 plasma jet result in better cleaning performance. In the He/O2 plasma jet or the Ar/O2 plasma jet, there exists an optimum O2 mixing ratio for a certain input power, at which the desirable cleaning performance can be received. And the highest removing rate is 1259.8 ng/s when the 2.1% O2 in the Ar plasma jet at an input power of 6 W. It is considered that atomic oxygen can be generated most efficiently under this optimum O2 mixing ratio.

A low-frequency (20–80 kHz) tube plasma source was designed for plasma beam generation at low pressure. In the atmosphere of pure nitrogen, the plasma source exhibited two distinct discharge states. The discharge sustained at low current (G mode) was a capacitive discharge and transited into a resistive discharge self-pulsing mode (SP mode) when the current exceeded a critical level. The SP-mode discharge was identified to be a mixing discharge consisting of continuous discharge and periodic sparks or pulsing arcs. Powered with 10–110 W, the SP-mode discharge created a plasma plume with high electron density (0.9– $5.1\times 10^{11}~\mathrm{cm}^{\mathrm {-3}})$ and relatively low electron temperature (1.62–0.55 eV). The vibrational and rotational temperatures of the SP-mode plasma in the tube were determined to be $\sim 5000$ K and 350–700 K by fitting the optical emission spectra, respectively, distinguishing from those of the G-mode discharge.

An experimental study of the effects of airflow, magnetic field, and combination of airflow with magnetic field on a nanosecond pulsed dielectric barrier discharge (DBD) in atmospheric air is presented. The DBD is generated by an in-house designed DBD structure (a metal rod is inserted into the traditional parallel-plate DBD). The experimental results show that the application of airflow to the DBD can reinforce discharge and improve the discharge uniformity. When airflow increases to a certain velocity, surface discharge can transform into diffuse volume discharge. Moreover, the application of a magnetic field to DBD in static air can also enhance discharge, which is manifested as the enhancement of surface discharge. A similar but more significant effect is obtained in DBD combined airflow with magnetic field. Compared with the DBD with airflow only, the transition from surface discharge to diffuse volume discharge in DBD combined airflow with magnetic field occurs at a smaller airflow velocity. Besides, DBD combined airflow with magnetic field under different pulse repetition frequencies (PRFs) is also investigated. The results show that the minimum velocity required to generate diffuse volume discharge also shrinks with the decrease in PRF. In short, it is easier to generate diffuse volume discharge under the conditions of airflow, magnetic field, and lower PRF. The underlying physical mechanism of the above phenomena is discussed and mainly ascribed to the enhanced ionization by applying airflow, magnetic field, and lower PRF.

The effects of driving frequency on plasma parameters and electron heating efficiency are studied in cylindrical inductively coupled plasma (ICP) source. Measurements are made in an Ar discharge for driving frequency at 13.56/2 MHz, and pressures of 0.4–1.2 Pa. In 13.56 MHz discharge, higher electron density (n e) and higher electron temperature (T e) are observed in comparison with 2 MHz discharge at 0.6–1.2 Pa. However, slightly higher n e and T e are observed in 2 MHz discharge at 0.4 Pa. This observation is explained by enhanced electron heating efficiency due to the resonance between the oscillation of 2 MHz electromagnetic field and electron-neutral collision process at 0.4 Pa. It is also found that the variation of T e distribution is different in 13.56 and 2 MHz discharge. For ICP at 13.56 MHz, T e shows an edge-high profile at 0.4–1.2 Pa. For 2 MHz discharge, T e remains an edge-high distribution at 0.4–0.8 Pa. However, the distribution pattern involves into a center-high profile at 0.9–1.2 Pa. The spatial profiles of n e remain a center-high shape in both 13.56 and 2 MHz discharges, which indicates the nonlocal kinetics at low pressures. Better uniformity could be achieved by using 2 MHz discharge. The effects of gas pressure on plasma parameters are also examined. An increase in gas pressure necessitates the rise of n e in both 13.56 and 2 MHz discharges. Meanwhile, T e drops when gas pressure increases and shows a flatter distribution at higher pressure.

An atmospheric pressure plasma jet generated in Ar and O2/Ar mixtures has been investigated by specially designed equipment with double power electrodes at 20~32 kHz, and their effects on the cleaning of surfaces have been studied. Properties of the jet discharge are studied by electrical diagnostics, including the waveform of discharge voltage, discharge current and the Q-V Lissajous figures. The optical emission spectroscopy is used to measure the plasma parameters, such as the excitation temperature and the gas temperature. It is found that the consumed power and the excitation temperature increase with increase of the discharge frequency. On the other hand, at the same discharge frequency, these parameters in O2/Ar mixture plasma are found to be much larger. The effect on surface cleaning is studied from the changes in the contact angle. For Ar plasma jet, the contact angle decreases with increase of the discharge frequency. For O2/Ar mixture plasma jet, the contact angle decreases with increase of discharge frequency up to 26 kHz, however, further increase of discharge frequency does not show further decrease in the contact angle. At the same discharge frequency, the contact angle after O2/Ar mixture plasma cleaning is found to be much lower compared to the case of pure Ar. From the results of quadrupole mass-spectrum analysis, we can identify more fragment molecules of CO and H2O in the emitted gases after O2/Ar plasma jet treatment compared with Ar plasma jet treatment, which are produced by the decomposition of surface organic contaminants during the cleaning process.

In this paper, an atmospheric pressure argon plasma jet generated by sinusoidal power input of moderate frequency (kHz range) and designed with dual-power electrodes is characterized and studied. Particularly, the effect of driving frequency in the 60–130 kHz range on the argon plasma discharge characteristics is investigated based on the electrical and spectroscopic diagnostics. It is shown that at constant applied voltage and gas flow rate, the increase of driving frequency in the range of 60–100 kHz exerts no significant influences on discharge parameters. While once the driving frequency exceeds a certain value of about 100 kHz, the discharge becomes intense abruptly and the corresponding discharge parameters increase drastically with the driving frequency. Detailed analysis about the effect of driving frequency on discharge characteristics is presented and two different dominant electron loss mechanisms, namely transport-dominated loss and diffusion-dominated loss, are proposed to account for the distinct effects of the driving frequency on argon discharge characteristics.

In this paper, a cold atmospheric plasma (CAP) jet array is generated by a 2-D array device of seven CAP jets arranged in a honeycomb configuration and designed with single-electrode configuration as the elemental plasma jet. The work is motivated by the challenge of using inherently small atmospheric plasmas to address many large-scale processing applications. The discharge characteristics of the plasma jet array are investigated based on detailed electrical, spectroscopic, and imaging characterizations. The CAP jet array is shown to achieve good temporal jet-jet uniformity. Furthermore, the dynamic behavior of the jet discharges is studied particularly through two series of intensified-charge-coupled-device images taken at the end views. It has been found that the seven jets show a good temporal synchronization and jet-jet uniformity, as well as rich dynamics of jet-jet interactions such as a slight repulsion at surrounding jet heads, particularly for a small gas flow rate of helium. These dynamic features offer possible insights with which to better control the jet-jet interactions and further optimize the design of large-scale CAP sources.

A cold Ar atmospheric pressure plasma jet generated using a DBD configuration device equipped with two powered electrodes as well as a grounded ring electrode driven by a sinusoidal excitation voltage at 38 kHz is presented in this paper. In this paper, properties of the jet discharge are studied by electrical diagnostics, including applied voltage, conducting current, and average absorbed power. Moreover, the optical emission spectroscopy is used to measure the plasma parameters, of which the electronic excitation temperature is determined by the Boltzmann's plot method using ten characteristic lines of Ar from 3p54p → 3p54s and 3p55p → 3p54s transitions whereas the gas temperature is obtained by using a fiber thermometer (FISO FOT-L-SD). It has been found that the conducting current, average absorbed power, the excitation temperature, and gas temperature increase with the applied voltage. On the other hand, these parameters are inversely proportional to the argon gas flow rate. What is more is that the production of oxygen radical (produced by the collisions between oxygen molecule from atmosphere and high-energy particles in plasma effluent) at a gas flow rate of 2 slm is investigated by means of optical actinometry, which is found to increase with the applied voltage.

This paper illustrates a repetitive nanosecond volume discharge in the airflows at different velocities. The plasma images presented here show that the volume discharge modes vary with the changes of airflow speeds, and a diffuse and homogeneous volume discharge occurs at the airflow speed of 30 m/s. The discharge is promoted in the airflows at a lower velocity, and the discharge tends to be inhibited at a speed to 40 m/s. However, the inhibited mode disappears at higher repetitive frequency of the pulse.

Dielectric barrier discharge (DBD) with better uniformity, excited by nanosecond pulses, is achieved within 8 mm air gap by using a self-designed DBD structure in airflow. The self-designed DBD structure is characterized by adding a metal rod (MR) in discharge gap, which will produce a local strong electric field and induce surface and volume discharge. It is observed from sequential single periodic discharge images that the uniformity of discharge starts from the electrode edge at the airflow inlet and moves gradually toward downstream under the action of airflow. When the uniformity of discharge is transmitted to a nearby of MR, a stable uniform and symmetrical annular discharge configuration is formed. Besides, that uniform area can be expanded by adding many MRs or MR array in the discharge gap. There is an optimum distance between every two MRs to produce a continuous and maximum discharge area with better uniformity. The above phenomena are mainly ascribed to the change of electric field distribution caused by MR and the charged particles redistribution induced by airflow.

In this paper, a two-dimensional axisymmetric fluid model is applied to investigate the streamer discharge characteristics in an atmospheric pressure methane-air plasma jet as a function of methane flow velocities (2.5 m/s and 20 m/s, respectively). Although the streamer ignition and propagation in the dielectric tube are not sensitive to the methane gas flow velocity, the concentration field of methane and air in the mixing layer established by a balance between convective methane flow and back-diffusion of air ambient is crucial for streamer propagation in the gap. As the methane flow velocity is 2.5 m/s, the structure of the streamer head transits from ring-shape into solid disk-shape, while the streamer head always maintains a donut-shaped pattern at high flow velocity of 20 m/s until it impinges on the substrate. At lower gas velocity, the back-diffusion of ambient air into the methane jet is even more pronounced, which causes a larger space charge density at the streamer head, and thus the local electric field near streamer head is greater. Therefore, the overall trend in streamer propagation speed versus methane flow velocity is that the larger the flow velocity, the lower plasma bullet speed. Besides, as the gas flow velocity increases from 2.5 to 20 m/s, less oxygen/nitrogen radical species and charged ions are produced in the streamer discharge, while the produced methane-related particles increase slightly. As for different methane flow velocities, the streamer advances within the methane core.

In this paper, a detailed fluid model is developed for the conversion of methane to methanol with hydrogen peroxide vapor in an atmospheric dielectric barrier discharge. The two-dimensional axisymmetric fluid model is constructed, in which 107 plasma chemical reactions and 28 different species are considered. Our attention is focused on physicochemical mechanism of methanol formation during the complicated chemical reaction processes of reactant molecules dissociation by electron impacting and neutral radical recombination. First, spatial and temporal characteristics of main radicals and ions, such as H, CH3, OH, CH3OH, CH3O, CH2OH, CH4 +, CH3 +, H2O2 +, and H2O+, are presented. It is found that the streamer discharge is sustained by the direct electron-impact ionization of methane molecules. The dominant positive ion flux on to the dielectric surface is methane ion, and its peak value is located at axis. Then, the dominant chemical routes governing the production and loss of CH3OH and OH are discussed in detail. Finally, a schematic overview of dominant plasma reaction pathways for partial oxidation of methane to methanol with hydrogen peroxide vapor in atmospheric dielectric barrier discharge is summarized.

Long term exposure to arsenic can cause adverse health effects and lead to different levels of disability. The prevalence of arsenical dermatosis is as high as 40% in the Hetao Plain area of Inner Mongolia, but the association between exposure to arsenic in drinking water and the occurrence of disability has not yet been fully examined. The aim of this study was to investigate the prevalence of disability in arsenic-affected villages in Inner Mongolia, China.A cross-sectional study was performed to examine the prevalence of disability. A total of 320 villagers in the age range of 20-39 years were interviewed and examined for disability and arsenical skin lesions. The subjects were classified into a high arsenic group (50 microg L(-1)) and a low arsenic group (50 microg L(-1)). The relationship between levels of arsenic in drinking water and disability was analyzed using multivariate logistic regression models to estimate the odds ratios and 95% confidence intervals.The prevalence of disability was 6.88% in the arsenic affected area of Inner Mongolia and 24.72% in the arsenic group 50 microg L(-1). A strong correlation was found between disability and arsenical skin lesions (OR=86.39, 95%CI: 25.45-293.20).This suggests that the level of arsenic exposure is a major risk factor for disability. Further research is needed to place the results in a wider context and to determine the exact relationship between arsenic exposure and disability.

Experimental investigations of the breakdown characteristics of plate-to-plate dielectric barrier discharge excited by an AC source at different gas flow conditions are carried out. The ignition voltage for the appearance of the very first discharge filament and the breakdown voltage in each discharge half cycle in continuous operation are examined. As revealed by the results of the indoor air experiment, the ignition voltage manifests a monotonous increase with the increase in the gas flow rate, while the breakdown voltage has a marked decline at the low gas flow rate and increases slightly as the gas flow rate is higher than 10 m/s. As regards the obvious decreases in the ignition voltage and breakdown voltage, the decrease in the humidity with the increase in the gas flow rate plays a dominant role. As regards the increase in breakdown voltage, the memory effect from the preceding discharge is considered. The losses of metastable particles, together with particles having high translational energy in the gas flow, are considered to be the most critical factors.

Atmospheric-pressure dielectric barrier discharge (DBD) with airflow participation has been widely used in recent years. In this paper, effects of airflow on DBD characteristics are experimentally investigated by single/double pin-to-plate DBD arrangements with an AC exciting source. The discharge electrical characteristics and the movements of discharge channels in airflow are investigated with a single pin electrode arrangement. The current intensities increase in positive cycles and decrease in negative cycles with the increase in airflow velocity. The transition from a filamentary discharge to a diffuse discharge is observed under certain airflow conditions, and the discharge channels move with the airflow with a movement velocity less than the corresponding airflow velocity. In the cases of double pin electrode arrangements, the repulsion between double pin discharge channels is apparent at a 10 mm distance but is not obvious at a 20 mm distance. When the airflow is introduced into the discharge gap, not as in the case of single pin electrode arrangement, the movements of discharge channels in airflow are affected by adjacent discharge channels. The corresponding reasons are analyzed in the paper.

In this paper, a rich variety of self-organized patterns have been observed in a dielectric barrier discharge helium plasma jet generated at atmospheric pressure. It has been found that the evolvement of a discharge pattern in plasma jets is sensitive to diverse experimental parameters, including the applied voltage, the frequency of power, the scale of plasma jet generator, and the gas flow rate. By altering the applied voltage and/or the gas flow rate, the plasma jet is seen to evolve through three modes, which are diffuse-looking discharge, self-organized discharge with regular channels, and unstable discharge with random filaments. Among which, the self-organized discharge mode is characterized with several bright plasma channels stably formed in a straight line. The maximum number of channels is mainly determined by the scale of plasma jet generator. When the frequency is fixed, the minimum distance between two adjacent discharge channels in the self-organized mode is nearly the same, no matter what size tube is selected.

With three additional magnetic rings being assembled outside the discharge room and connected with the magnetic field of the conventional unbalanced magnetron sputtering, a closed magnetic field configuration distribution had been formed in the whole discharge room and which can confine discharge plasma more effectively. The spatial distribution of the newly designed magnetic field configuration was simulated using the ANSYS software. Plasma potential, electron temperature, electron density and ion density in the discharge plasma were diagnosed by Langmuir probe and the optical emission line intensity ratios of Ar + /Ar and Cu + /Cu were studied by optical emission spectroscopy. The structure and morphology of the Cu films are measured by scanning electron microscopy. A comparative study of the new magnetic field configuration with the conventional unbalanced magnetic field configuration was conducted. The results showed that the application of the additional magnetic field can increase the plasma density, enhance the ionization degree of the sputtered Cu and decrease the plasma potential effectively. The characteristics of the deposited Cu film were also influenced by the new magnetic field configuration greatly.

Most studies concerned with the interactions between plasma discharges and bacteria have mainly focused on the germicidal effects and inactivation mechanisms, with little attention given to the survivor bioeffects, such as changes in metabolism. This paper investigated the production of 1,3-propanediol (1,3-PD) from glycerol by Klebsiella pneumoniae after exposure to dielectric barrier discharge (DBD) plasma in air at atmospheric pressure. Increase in 1,3-PD production as determined from flask culture was dependent on treatment time, and the highest production was observed for cells that were treated with DBD plasma for 4 min. Changes in the specific activities of the three key enzymes (glycerol dehydrogenase, glycerol dehydratase, and oxidoreductase) involved in the conversion of glycerol to 1,3-PD were detected in the extracts of treated cells. Increase in 1,3-PD production correlated with an increase in the activity levels of all three enzymes. Batch-fermentation results showed that DBD plasma-treated cells had a 59% increase in both 1,3-PD production (23.8 g/L versus 15 g/L) and productivity (1.19 g/L middoth versus 0.75 g/L middoth) over untreated cells. DBD plasma, therefore, can alter the metabolic activities of K. pneumoniae, resulting in enhanced production of 1,3-PD.

In this paper, surface modification of polyethylene (PE) films is studied by dielectric barrier discharge plasma treatment in air. The treated samples were examined by water contact angle measurement, calculation of surface free energy, Fourier transform infrared attenuated total reflection spectroscopy (FTIR-ATR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The water contact angle changes from the original value of 93.2° to the minimum value of 53.3° and surface free energy increases from 27.3 to 51.89 J/m 2 after treatment time of 50 s. Both ATR and XPS show some oxidized species are introduced into the sample surface by the plasma treatment and that the change tendencies of the water contact angle and surface free energy with the treatment time are the same as that of the oxygen concentration on the treated sample surface. Cu films were deposited on the treated and untreated PE surfaces. The peel adhesive strength between the Cu film and the treated sample is 1.5 MPa, whereas the value is only 0.8 MPa between the Cu film and the untreated PE. SEM pictures show that the Cu film deposited on the plasma treated PE surface is smooth and the crystal grain is smaller, contrarily the Cu film on the untreated PE surface is rough and the crystal grain is larger.

In this paper, three permanent magnet rings, which were placed alternatively between the three antenna coils of a cylindrical inductively coupled radio frequency (rf) argon plasma for rf enhanced ionized magnetron sputtering system, were used to produce a closed magnetic field distribution with the magnetic field of the unbalanced magnetron sputtering to confine discharge plasma. Langmuir probe measurement was used to study the effect of the magnetic field on the plasma characteristics and their spatial distribution. The results show that the presence of the closed magnetic field leads to the increase of the ion density and the decrease of electron temperature and plasma potential. With the closed magnetic field, the plasma density distribution in radial direction will become more uniform.

Plasma treatment can effectively modify the surface characteristics of fabrics, such as wettability, dyeability and adhesion strength. In this paper, dielectric barrier discharge (DBD) in ambient air is applied to modify linen surface and improve the grafting efficiency and dyeability. Scanning electron microscope (SEM) shows that DBD treatment can effectively change the surface morphology of the treated linen. Raman spectrum, SEM and Fourier transform infrared spectroscopy conform that graft reaction certainly takes place on the DBD-treated linen surface. The dyeability improves with the increase of grafting efficiency, which shows that graft has a great effect on dyeability. For the grafting efficiency and dyeability, the optimal DBD treatment time is 30 s in this experiment. The possible reason may be that, with the increase of the treatment time, the surface degradation will become strong, which will lead to the invalidation of some already modified results.

Conical dc discharge is generated between a copper cathode with a hemispherical head (2-7 mm in diameter) and a static water anode in ambient air. The discharge is hollow and is just like an umbrella if the electrical conductivity of the water electrode is higher than 17.31 musldrcm-1. The profile is composed of three zones with different luminosities. The effects of the discharge current, air gap length, cathode dimension, and electrical conductivity of the water electrode on the discharge are studied. Volt-ampere characteristics and images of the discharge under different experimental conditions are shown to characterize the discharge. A mechanism for stabilizing the discharge is discussed.

Linen fabric is an excellent material due to its wettability, permeability to air and electrostatic resistance. However, the difficulty of dyeability is a main disadvantage for its practical applications. Graft co-polymerization of acrylic acid (AAc) onto the linen surface induced by dielectric barrier discharge (DBD) in air can effectively improve the dyeability. The paper mainly studied the ability of graft co-polymerization AAc onto linen surface by DBD treatment in air. The AAc grafted on linen surface was characterized by differential thermal analysis, scanning electron microscopy and Fourier transform infrared attenuated total reflection spectroscopy. The grafting degree was measured by visible absorption spectroscopy. The effects of plasma treatment time, grafting time, grafting temperature and grafting solution concentration on the grafting degree were studied and discussed.

Optical emission spectroscopy has been performed for unbalanced DC magnetron sputtering of Cu in Ar atmosphere with the enhanced ionization of inductively coupled plasma. The intensities of Cu, Cu + , Ar and Ar + lines were measured at various discharge parameters such as pressure and rf power. Both Cu and Cu + lines intensities initially increase and then decrease with increasing pressure. At the same time, Ar line intensity increases and the Ar + line intensity decreases with increasing pressure. With increasing rf power, all the lines intensities increase at different rates and become saturated when the rf power is greater than 700 W. The rf discharge exhibits mode jumping (E-mode to H-mode) and hysteresis phenomena. When the rf power increases to 400 W, the rf discharge mode jumps from E-mode to H-mode. When the rf power input decreases from 800 to 300 W, the rf discharge mode jumps back from H-mode to E-mode. However, during the mode change, the intensities of all lines are higher when switching from H-mode to E-mode than those when switching from E-mode to H-mode at the same rf power. In the rf power region, the ionization of Cu is significantly enhanced. The reasons of these phenomena are discussed.

In a multi-pin-to-multi-cupped-plane DC negative corona discharge configuration, a stable and diffuse glow discharge controlled by a fast airflow was obtained. This paper investigates the effect of the air gas flow velocity and the electrode structure on the discharge mode transition and the stabilization of the glow discharge by means of electric measurements and emission records. The stabilization mechanism of the glow discharge is discussed. The maximum glow discharge current reached 3.9 mA and the average current density was about 0.7 mA/cm2.

To reveal the inactivation mechanism of microorganism in plasmas, a baker's yeast (Saccharomyces cerevisiae) sample is exposed in dielectric barrier discharge plasma in helium at atmospheric pressure. The mitochondrial activity charactering the survival probability of the yeast cell is measured by the 3-(4, 5-dimethylthiazol-2-yl) 2, 5-diphenyl-tetrazolium bromide method. The results show that the survival probability of yeast cells sharply decreases within the exposure time of 1.0-2.5 min and almost remains constant as exposure time is longer than 2.5min. The increase of the protein concentration in the supernatant solution of yeast suspension indicates that the intracellular proteins leak to the extracellular environment when the cells undergo plasma exposure, and gross structural damage is observed by a scanning electron microscope. The possible cause of the rupture is the electrostatic tension produced by the charges accumulated on the cell surface in the plasma. In addition, the extracellular medium whose pH is changed may also contribute to the rupture of the treated yeast cells.

In this paper, a time-resolved study on the evolution process of the plasma channels in an atmospheric pressure plasma jet is performed by using a high-speed camera system and synchronous current-voltage measurement. We have succeeded in observing the plasma channels turn up at the same time, and propagate at the speed of about 4×103 m/s in the air. Once pattern formation is done, discharge channels are fixed at the same locations, even when the polarity of the applied voltage changes.

TiN films have many features, such as high wear resistance, high corrosion resistance and good oxidization resistance. With the technology of vacuum arc deposition and high current density nitrogen ion beam dynamic mixing implantation (DMI), the TiN film with a thickness of 33 μm and adhesion 58 N is synthesized on hard alloy and high-speed steel substrates. X-ray diffraction has been used to examine the crystal structure of the films. The results showed that the main phases presented in DMI films are TiN and Ti 2 N and that the films revealed random growth. Cross-sectional scanning electron microscopy revealed the dense morphology and the thickness of the films. Micro-hardness tests showed that the average hardness of the films was about 2500 HK. Electrochemical experimental results indicated that DMI-TiN film had excellent corrosion resistance both in 3% NaCl solution and in 0.5 Mol H 2 SO 4 solution.

In this study, we explored the surface roughness, scratch resistance and tribological properties of hydrogenated amorphous carbon (a-C:H) coatings deposited on silicon substrates from low-pressure dielectric barrier discharge (DBD) plasmas of CH 4 by using an atomic force microscope (AFM), AFM-based scratch testing technique and lateral force microscope. The AFM and scratch measurements show that the surface roughness and scratch resistance of these a-C:H coatings strongly depend on the Pd value (the product of CH 4 pressure P , and discharge gas spacing d ) and the a-C:H coatings deposited at suitable Pd value (typically 350 Pa mm) exhibit lower surface roughness and better scratch resistance. The a-C:H coatings deposited at the Pd value of 350–1750 Pa mm have the typical friction coefficient of approximately 0.13. The lower friction coefficient (0.11) of the a-C:H coating deposited at the smaller Pd value of 245 Pa mm can be associated with its graphite-like surface structure. The results indicate the coating structure changes from the one of graphite-like to diamond-like to polymer-like with the Pd value increasing from 245 to 1750 Pa mm. The relationship between the measured coating properties and the DBD deposition processes was presented.

The effects of a parallel magnetic field on the unipolar positive nanosecond pulsed dielectric barrier discharge are experimentally investigated through electrical and spectral measurements. The discharge is produced between two parallel-plate electrodes in the ambient air with a parallel magnetic field of 1.4 T. Experimental results show that both the discharge intensity and uniformity are improved in the discharge with the parallel magnetic field. The intensity ratio of the spectrum at 371.1 nm and 380.5 nm, which describes the average electron density, is increased by the parallel magnetic field. Meanwhile, the intensity ratio of the spectrum at 391.4 nm and 337.1 nm, which describes the electron temperature, is also increased. It is speculated that both the average electron density and the electron temperature are increased by the parallel magnetic field. The aforementioned phenomena have been explained by the confinement effect of the parallel magnetic field on the electrons.