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High-energy electron beam can be generated during the breakdown process in a gas diode at elevated pressures. The design of electrodes in the gas diode affects the parameters of these electron beams. In this paper, investigation on parameters of the runaway electron beam (REB) in air and nitrogen excited by nanosecond pulsed generators are presented. Experiments were carried out with gas diodes by using cathode and anode made of different materials, including stainless steel, aluminum, copper and titanium. Experimental results show that, in the case of nanosecond-pulse breakdown, the cathode material significantly affects the amplitude of the REB current pulse when either pressure or gap spacing are small. When the pressure is low, the REB current is highest for the stainless steel cathode due to its small electron work function. However, the REB current for the aluminum, copper and titanium cathodes is higher than that of stainless steel cathode at atmospheric pressure because of the Malter effect on their surfaces. The dependence of the amplitude of the REB current on the anode foils is investigated by using aluminum, titanium, copper and tantalum. The experimental results show that the atomic number of the metal, as well as mass mean free path of the electron in it contribute to the amplitude of the REB current pulse. Based on the REB currents of different anode foils, energy distribution of runaway electrons is estimated. Electron distribution with an average energy of ~55 keV is obtained when the amplitude of the applied voltage pulse across the discharge gap is 110 kV. The results may contribute to the design of the gas diode for the generation of high-energy electron beams in nanosecond-pulse breakdown. [ABSTRACT FROM AUTHOR]

A double layer DBD plasma jet driven by a pulsed generator is used for SiOx thin film deposition. The effects of dielectric and conductive targets on discharge behavior and film properties are analyzed. Different fraction of N2 is added to the working gas (argon) to modulate film growth rate. The electrical property and optical emission of the plasma jet at different positions are characterized. Film surface morphology, composition and thickness are measured for different targets. The excitation temperature (Texc), vibrational temperature (Tvib) and rotational temperature (Trot) are calculated. The relationship between the discharge behavior and the film properties is studied. Results show that the relative optical emission intensities of Si, O, Ar and N2, as well as Texc, Tvib and Trot are higher for the PMMA target between the high voltage electrode and the grounded electrode (referred to as the H–G region). However, Tvib and Trot appear to be higher on the surface of the copper (conductive) target. The morphology of SiOx film is different: nanoparticles are formed on the PMMA (dielectric) target while dense amorphous film is formed on the copper target. With the same depositing parameters, the thickness of the SiOx film is higher on the copper target. The presence of PMMA at the downstream of the plasma can be considered as a small capacitor with a large resistance, which inhibits the current into the primary circuit passing through the H–G region. Although the presence of a dielectric target enhances the discharge in the H–G region, the charge accumulation on the PMMA surface limits the film growth. These results may contribute to the development of next-generation plasma surface modification technologies for diverse applications in electronics, material synthesis and other related areas. [ABSTRACT FROM AUTHOR]

Repetitively pulsed discharge is an emerging non-thermal plasma technology in the chemistry field given its advantages of high electron energy and moderate gas temperature. The focus of this paper is on the temporal evolution of physical and chemical processes in the plasma-assisted non-oxidative conversion of methane (CH4). Positive and negative streamer discharge plasmas were generated by a microsecond-pulse power source (pulse rising time ~500 ns and full width at half maximum ~8 μs) in a well-designed dielectric barrier discharge reactor. The performance of CH4 conversion (conversion rate, product yield, energy conversion efficiency, etc) was investigated in the first instance. A CH4 conversion rate of 6.2%–9.6% was acquired in the negative streamer discharges, which is on average 6% higher than that in the positive streamer discharges. To explain this phenomenon, the temporal evolution of voltage–current waveforms and ultrafast ICCD photographs and optical emission spectra were recorded. As expected, significant differences between the two different forms of discharges were found. Compared with those of the positive streamer discharges, characteristics of only one, big breakdown, higher initial voltage and current peak, a more stable and nearly uniform luminescent process, and higher CH (A2Δ  −  X2Π) emission intensity and rotational temperature were observed in the negative streamer discharges, which coincide with the promotion of CH4 conversion performance. A simplified chemical kinetics analysis of CH4 discharge was also implemented to demonstrate the influence of characteristic differences on CH4 conversion performance. [ABSTRACT FROM AUTHOR]

In this paper, deposition by non-thermal plasma is used as a surface modification technique to change the surface characteristics of epoxy resin exposed to DC and nanosecond-pulse voltages. The corresponding surface characteristics in both cases of DC and nanosecond-pulse voltages before and after the modification are compared and investigated. The measurement of the surface potential provides the surface charge distribution, which is used to show the accumulation and dissipation process of the surface charges. Morphology observations, chemical composition and electrical parameters measurements are used to evaluate the treatment effects. The experimental results show that, before the plasma treatment, the accumulated surface charges in the case of the DC voltage are more than that in the case of the nanosecond-pulse voltage. Moreover, the decay rate of the surface charges for the DC voltage is higher than that for the nanosecond-pulse voltage. However, the decay rate is no more than 41% after 1800 s for both types of voltages. After the plasma treatment, the maximum surface potentials decrease to 57.33% and 32.57% of their values before treatment for the DC and nanosecond-pulse voltages, respectively, indicating a decrease in the accumulated surface charges. The decay rate exceeds 90% for both types of voltages. These changes are mainly attributed to a change in the surface nanostructure, an increase in conductivity, and a decrease in the depth of energy level. [ABSTRACT FROM AUTHOR]