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The synthesis of the nanopowders of magnesium oxide and magnesium fluoride during the operation of a repetitive diffuse nanosecond discharge in argon at various pressures was performed. Nanosecond voltage pulses with an amplitude of −70 kV, a rise time of 0.7 ns, and a duration of 0.7 ns were applied across a point-to-plane gap of 2 mm in length. The pulse repetition rate was 60 Hz. The high-voltage pointed electrode was made of magnesium. A diffuse discharge cold plasma was formed under these conditions. Nanoparticles were produced as a result of an explosion of microprotrusions on the surface of the magnesium electrode duo to a high current density. Lines of magnesium atoms and ions were observed in the emission optical spectrum. Under the actions of the gas dynamics processes caused by the plasma channel expansion during the interpulse period, nanoparticles were deposited onto the surface of the grounded plane electrode and the side wall of the gas discharge chamber. The morphology, elemental, and phase composition of the powders were studied using transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). [ABSTRACT FROM AUTHOR]

Features of the nanosecond discharge development in a non-uniform electric field are studied experimentally. High spatial resolution imaging showed that thin luminous tracks of great length with a cross-section of a few microns are observed against the background of discharge glow in air and argon. It has been established that the detected tracks are adjacent to brightly luminous white spots on the electrodes or in the vicinity of these spots, and are associated with the flight of small particles. It is shown that the tracks have various shapes and change from pulse to pulse. The particle tracks may look like curvy or straight lines. In some photos, they can change their direction of movement to the opposite. It was found that the particle's track abruptly breaks and a bright flash is visible at the break point. The color of the tracks differs from that of the spark leaders, while the bands of the second positive nitrogen system dominate in the plasma emission spectra during the existence of a diffuse discharge. Areas of blue light are visible near the electrodes as well. The development of glow and thin luminous tracks in the gap during its breakdown is revealed using an ICCD camera. Physical reasons for the observed phenomena are discussed. [ABSTRACT FROM AUTHOR]

The streamer formation in a point-to-plane gap filled with atmospheric-pressure air has been experimentally studied using a streak camera and a four-channel intensified charge-coupled device camera with simultaneously recording waveforms of voltage and discharge current pulses. A large diameter streamer was observed at various amplitudes of nanosecond voltage pulses. The instantaneous streamer velocity was measured using the streak camera. It was found that the streamer has a high velocity at the initial stage of development, but it rapidly decreases. The minimum streamer velocity corresponds to the maximum diameter. The streamer velocity increases again by an order of magnitude when it approaches the opposite electrode. It was found that the streamer velocity correlates with the value of a displacement current induced by its propagation. At the initial stage of the streamer development during subnanosecond breakdown, the displacement current can reach several kiloamperes; this is comparable to the conduction current after the breakdown. [ABSTRACT FROM AUTHOR]

The results of a study of the processes involved in the production of indium oxide In2O3 powder, which is widely used to create transparent and electrically conducting ceramics, are described. The powder was produced in a flow of rare gas (argon or helium) at atmospheric pressure under conditions for the formation of metal-containing plasma in a non-arc discharge mode. The discharge operated in pulsed mode with a pulse repetition rate of 70 kHz and pulse duration of 12 μs. The discharge current was 670 mA and discharge voltages were 180 V and 250 V when the working gases were argon and helium, respectively. These parameters ensure a mode in which the indium cap of a molybdenum cathode suffers thermal erosion. The morphology and elemental and phase composition of the erosion products were studied using transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) analysis. It was shown that the structure of the synthesized powder particles corresponded to a phase of indium oxide (III) with a body-centered cubic (bcc) lattice with lattice parameter a = 1.013 nm. The powder particles, regardless of the working gas (Ar or He), consisted of non-stoichiometric indium oxide In2O3 with a nanocrystalline structure. The average particle diameter was = 13–16 nm. [ABSTRACT FROM AUTHOR]