Transient behavior of drift and ionization in atmospheric pressure nitrogen discharge

The fluid models are frequently used to describe a non-thermal plasma such as a streamer discharge. The required electron transport data and rate coefficients for the fluid model are parametrized using the local field approximation (LFA) in first order models and the local-mean-energy approximation (LMEA) in second order models. We performed Monte Carlo simulations in Nitrogen gas with step changes in the E/N (reduced electric field) to study the behavior of the transport properties in the transient phase. During the transient phase of the simulation, we extract the instantaneous electron mean energy, which is different from the steady state mean electron energy, and the corresponding transport parameters and rate coefficients. Our results indicate that the mean electron energy is not a suitable parameter for mobility/drift of electrons due to big difference in momentum relaxation and energy relaxation. However, the high energy threshold rates such as ionization show a strong correlation to mean electron energy. In second order models where the energy-balance equation is solved, we suggest that it would rather be appropriate to use the local electric field to find electron drift velocity in gases such as Nitrogen and the local mean electron energy to determine the ionization and excitation rates.

GAS TEMPERATURE MEASUREMENT IN THE ACTIVE ZONE OF STREAMER DISCHARGE UNDER DIFFERENT APPLIED VOLTAGES

The experimental results on the gas temperature measurement in the active zone of streamer discharge in air at the atmospheric pressure are presented. The gas temperature value was obtained by the optical method for measur-ing the relative intensity of the rotational lines for the radiation of the second positive (II+) system of molecular ni-trogen, transition bands (С3Пu(0)→B3Пg(0)). It was found that in discharge gap d = 8 mm, depending on the ap-plied voltage (in the range of 6.1…7.8 kV with a step of 0.2 kV), the gas temperature varied from 609 to739 K. The unevenness of the gas temperature change in the active zone of discharge with the increase in the applied voltage is shown. This may be related to the possible changes in the rotational state of nitrogen molecules upon excitation of their electronic state by electrons.

Characteristics of pulsed nanosecond discharge excited by compact solid-state pulse forming line at atmospheric pressure air

Non-equilibrium plasma is a promising technology for the generation of ozone and removal of exhausted fuel gases. However, applications of non-equilibrium plasma are restricted by energy utilization efficiency in many industry fields. Discharge excited by nanosecond pulsed power is regarded as one of the most efficient methods. In this study, a compact 5 stages stacked blumlein pulse forming line and photoconductive semiconductor switches-based power source was introduced to generate pulsed plasma. This compact source could achieve over 50 kV with 10.1 ns pulse width and 4.8 ns pulse rising time. Coaxial cylindrical reactor was employed to generate a pulsed streamer discharge driven by the nanosecond pulsed source in atmospheric pressure air. Electrical parameters of the streamer discharge have been obtained in this study, the instantaneous power dissipation exceeds 8 MW and the average energy consumption of each pulse exceeds 56 mJ. Experiments of high speed photography have been conducted to observe the evolution process. It can be found that streamer heads start from the central wire electrode and then head to the grounded cylinder electrode in all radial direction of the coaxial electrode. Triple wire-to-cylinder electrodes discharge shows that all the three coaxial discharges develop synchronously and symmetrically, which shows that is capable of generating large volume non-equilibrium diffusive streamer discharge plasma.

Nanosecond breakdown in a pulsed open discharge

The paper presents the results of studies of open discharge breakdown characteristics at nanosecond supply pulse in helium, neon, argon working medium in a wide pressure range. It is shown that the open discharge exists in the range of p He = 20–100 Torr, pNe = 1.5–25 Torr, p Ar = 0.5–3.7 Torr with used experimental conditions. With increasing pressure, the role of separate elementary processes increases which can lead to a change of the discharge form to a presumably avalanche or streamer discharge. However, in this case, due to the photoemissive nature of the open discharge initiation, the similarity law Ep = f(pι) does not coincide with that for a nanosecond avalanche discharge.

Influence of Silicone Rubber Coating on the Characteristics of Surface Streamer Discharge

A pollution flashover along an insulation surface—a catastrophic accident in electrical power system—threatens the safe and reliable operation of a power grid. Silicone rubber coatings are applied to the surfaces of other insulation materials in order to improve the pollution flashover voltage of the insulation structure. It is generally believed that the hydrophobicity of the silicone rubber coating is key to blocking the physical process of pollution flashover, which prevents the formation of continuously wet pollution areas. However, it is unclear whether silicone rubber coating can suppress the generation of pre-discharges such as corona discharge and streamer discharge. In this research, the influence of silicone rubber coating on the characteristics of surface streamer discharge was researched in-depth. The streamer ‘stability’ propagation fields of the polymer are lower than that of the polymer with silicone rubber coating. The velocities of the streamer propagation along the polymer are higher than those along the polymer with silicone rubber coating. This indicates that the surface properties of the polymer with the silicone rubber coating are less favorable for streamer propagation than those of the polymer.

Oscillation of Gas Density in the Gas Filament Remained by a Streamer Discharge in Water

When a streamer discharge occurs in water, several luminous plasma filaments will be created in the water during the discharge. After the discharge, these plasma filaments turn into neutral gas phase and remain in water. The gas filament remained in water is a good object for studying the basic processes involved in the streamer propagation. We investigated the evolution of the gas filaments remained in water after a streamer discharge at different experimental conditions. We recorded eight successive images during one discharge pulse. The density of gas in the gas filament and the radius of the gas filament were measured from the obtained images. We found that the radius of the gas filament and the density of gas in the gas filament are almost not influenced by the impulse voltage within the range studied. While the conductivity of water has strong effect on the radius of the gas filament and the density of gas in the gas filament. The radius of the gas filament becomes thicker and expands faster as the conductivity of water becomes larger. The density of gas in the gas filament remained in water oscillates between 400 to 800 kg/m3 with an duration of ~10 μs during the expansion period of 4–39 μs after the HV pulse starts. Both the impulse voltage and the conductivity of water do not affect the oscillation duration of the density of gas in the gas filament.