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A homogeneous discharge with a large volume is a desirable plasma source for many applications. Nanosecond-pulsed high-voltage (HV) excitation is believed to be a promising strategy for obtaining homogeneous or diffuse discharges at atmospheric pressure. In this paper, using a knife–plate geometry driven by a nanosecond-pulsed generator, a diffuse plasma sheet with a gap distance of 1 cm and a length of 12 cm is generated in atmospheric air, maintaining a low gas temperature of ∼330 K. However, time-resolved images reveal that the discharge, which appears diffuse to the naked eye, actually consists of multiple individual streamers that propagate from knife (HV) to plate (ground). The appearance of two processes, namely primary and secondary streamers, is consistently verified by discharge images, electric field evolution and fluid simulation. This further proves that the entire discharge belongs to an intermediate state between corona and spark. This work aids a deeper understanding of the intrinsic characters of similar diffuse discharges and optimizing parameters in practical applications.

Measurement of runaway electron beam (REB) is essential to investigate behavior of runaway electrons produced in nanosecond-pulse gas discharge. A Faraday cup is designed to measure the REB current in nanosecond-pulse discharge when the applied dV/dtis 75 kV/ns. The Faraday cup considers the impendence match with the oscilloscope and the design of the receiving part. The experimental results show that the measured REB current has a rise time of 348 ps and a full width at half maximum of 510 ps. The comparison of the measurement results by the Faraday cup and a REB collector confirm that the Faraday cup is able to measure REB current in nanosecond-pulse discharge. Furthermore, consecutive waveforms of the REB currents show stable results by using the designed Faraday cup. In addition, effects of the interelectrode gap, gas pressure, and cathode material on the REB current are investigated by the designed Faraday cup, and the measurement results provide characteristics of REB current under different conditions. The REB current decreases when the gap spacing or gas pressure increases. REB current increases with the cathode diameter. It indicates that the high-energy electrons are generated not only at the edge of the cathode but also on the side surface of the cathode.

This paper presents an experimental investigation of ionization waves’ (IWs’) propagation in a nanosecond-pulse dielectric barrier discharge at atmospheric pressure in air. The effect of the rise time and pulse duration on IW propagation is studied by an intensified charge-coupled device, and the mechanism of the discharge propagation is analyzed. The experimental results show that the discharge produced in the rise time of the applied voltage develops in a structure of discontinuous sphere, while the discharge produced in the falling time exhibits a continuous form due to the effect of space charge. Furthermore, the rise time of the applied voltage has a significant influence on the velocity of IWs, and the maximal velocity of IWs rapidly decreases from 0.08 to 0.008 mm/ns when the rise time of the applied voltage increases from 50 to 300 ns. However, the pulse width has almost no influence on the velocity of IWs. The electric field distortion caused by both the propagation of IWs and the accumulation of surface charges is responsible for the formation and propagation of IWs.

Plasma synthetic jet (PSJ) has a wide application prospect in flow separation suppression and boundary layer control. Comparing with traditional control methods, synchronous discharges of PSJ with high repetition frequency and high energy could achieve a better flow control effect because it can meet multi-angle, wide-range and long-time flow control requirements. In this paper, a microsecond-pulse power supply for synchronous discharges of three plasma synthetic jet actuators (PSJA) is developed. Parameters of output pulses are as follows: the maximum voltage pulse is 10 kV, the pulse repetition rate is 1000 Hz and the full width is 15 μs. The generator can withstand a discharge current with an amplitude of 320 A and a discharge energy of 150 mJ. The electrical characteristics of the synchronous discharges of PSJAs including the voltage-current waveforms, discharge images and Schlieren images are investigated. The experimental result shows that the microsecond-pulse generator could sustain three discharge channels in PSJAs when the output voltage is 10 kV. These discharge channels have preferable performance in synchronicity when the repetition frequency is 1000 Hz. Furthermore, the Schlieren images show that the power supply can sustain three PSJAs with a maximum jet velocity of up to 150 m/s.

This paper presents an experimental investigation into the runaway electron spectrum with a gas diode composed of a rough spherical cathode and plane anode under the excitation of a nanosecond-pulse generator in atmospheric air. The runaway electron beams are measured by a collector covered with aluminum foil with a thickness from 0 μm (mesh grid) to 50 μm. The energy spectrum is calculated by an improved Tikhonov regularization called the maximum entropy method. The experimental results show that the transition state of the discharge consisted of multiple streamer channels stretched from the cathode with glow-like plasma uniformly distributed over the anode. The number of runaway electrons measured by the collector is in the order of 1010 in atmospheric pressure air with a gap spacing of 5 mm and applied voltages of 70–130 kV. The cathode with a rough surface creates a more inhomogeneous electric field and larger emission site for the runaway electrons around the cathode, providing conditions for the coexistence of filamentary streamer and diffuse discharge. The reconstructed spectra show that the energy distribution of the runaway electrons presents a single-peak profile with energies from eU m/2–2eU m/3 (U m is maximal voltage across the gap).

Based on 112.5 km2 of 3-D seismic data and data of 8 prospecting wells drilled volcanic rocks in the 3rd member of the Paleogene Shahejie Formation in Hongxing area of the Eastern Sag of the Liaohe Depression, Bohai Bay Basin, three levels of volcanic interfaces (stage→edifice→lithofacies) of the intermediate-mafic volcanic formation are identified to reveal favorable prospecting facies through comprehensive studies on geology, well logging and seismic data in single well and multiple wells following the seismic volcano stratigraphy principle. According to stage interfaces, three volcanic stages were identified in the 3rd member of Shahejie Formation. One or more volcanic edifice-seismic facies were identified in each volcanic stage and volcanic facies-seismic facies were identified in each volcanic edifice-seismic facies. Based on single well points, we described volcanic edifices on well-tie seismic sections; identified volcanic bodies by extracting coherent seismic attribute (superimposed volcanic edifices) taking the volcanic stages as the units; then identified volcanic edifices and volcanic lithofacies by extracting waveform classification properties. Volcanic facies mapping were completed by constituting the relationship between the volcanic facies and the seismic facies in drilling wells, seismic cross sections and mappings. There are two types of plane volcanic facies sequences in the intermediate-mafic volcanic facies of this study area: volcanic conduit facies→extrusive facies (→explosive facies)→effusive facies→volcanic sedimentary facies, volcanic conduit facies (→explosive facies)→effusive facies→volcanic sedimentary facies. Among them, the near crater assemblage (volcanic conduit, extrusive and explosive facies) has better hydrocarbon shows and is the most favorable target of hydrocarbon exploration. Key words: intermediate-mafic volcanic rock, volcanic facies, seismic facies, volcanic stratigraphy, volcanic stage, Liaohe Depression

Propagation of ionization waves (IW s) in long glass tube has been investigated in the last decade as an efficient method for understanding gas breakdown progress. However, the interaction between IWs itself still not fully understood and therefore this paper presents the experimental investigation of IW s propagation and its interaction in a long glass tube under two nanosecond pulse sources with opposite polarity. The interaction between the positive and negative IWs is studied by an intensified charge coupled device (ICCD), and the mechanism of the discharge propagation is analyzed. The experimental results show that the discharge can be divided into three stages: 1. generation of positive polar ionizing waves with velocity of 0.33 cm/ns; 2. generation of negative IW and its interaction with positive ones; 3. the decay of the discharge with the luminance attenuation. Furthermore, the luminance of the discharge channel and the speed of the IW s are enhanced because of the conducted channel behind the positive IW and the encounter of negative and positive IWs. Besides, With the change of the direction of the air flow, the initial time, the speed or the luminance intensity of IW s almost remain unchanged, which indicates the main drive of the IW s is the electric filed rather than air flow.

The parameters of X-ray radiation and runaway electron beams (RAEBs) generated at long-pulse discharges in atmospheric-pressure air were investigated. In the experiments, high-voltage pulses with the rise times of 500 and 50 ns were applied to an interelectrode gap. The gap geometry provided non-uniform distribution of the electric field strength. It was founded that at the voltage pulse rise time of 500 ns and the maximum breakdown voltage Um for 1 cm-length gap, a duration [full width at half maximum (FWHM)] of a RAEB current pulse shrinks to 0.1 ns. A decrease in the breakdown voltage under conditions of a diffuse discharge leads to an increase in the FWHM duration of the electron beam current pulse up to several nanoseconds. It was shown that when the rise time of the voltage pulse is of 500 ns and the diffuse discharge occurs in the gap, the FWHM duration of the X-ray radiation pulse can reach ≈100 ns. It was established that at a pulse-periodic diffuse discharge fed by high-voltage pulses with the rise time of 50 ns, an energy of X-ray quanta and their number increase with increasing breakdown voltage. Wherein the parameter Um/pd is saved.

Nanosecond-pulse generator can sustain homogeneous DBD in a small gap at atmospheric pressure1. Time evolution of discharge of nanosecond-pulse DBD is essential for fundamental understanding of pulsed breakdown kinetics2. In this paper, a homogenous DBD is excited by a nanosecond-pulse generator, which has a rise time of 25 ns and a full width at half maximum of 50 ns. Time evolution of the homogenous is captured by ICCD images with a camera gate of 2 ns. In order to shows propagation of streamers in nanosecond-pulse DBD, ICCD images are taken from the front view, the side view and the top view, respectively. The results show that the breakdown appears first near the centre of the high-voltage electrode, followed by breakdown along the entire electrode within several nanoseconds. Note that the plasma emission in the centre of the gap starts decaying earlier than that in the rest of the gap. By the decay of the plasma emission, a luminous layer occurs near the dielectric surface, because electric field reduction in the gap to below breakdown level. The luminous layer lasts approximately 100 ns. After that, a weak emission in the gap is detected again, indicating the secondary breakdown. Furthermore, the side view images exhibit discharge dynamics during the nanosecond-pulse DBD in detail. The discharge develops as a surface ionization wave, originating near the edge of the high-voltage electrode, first extending down towards the dielectric plate, and subsequently propagating symmetrically on both side of the high-voltage electrode along the dielectric surface, with a nearly straight ionization front. The average speed of the surface ionization wave is approximately 0.05 mm/ns. In addition, the top-view images confirm the above propagation process, and the propagation distance of the ionization wave on the dielectric surface is about 3 mm.

Characteristics of plasma synthetic jet (PSJ) actuators driven by repetitive pulsed discharge have drawn much attention. In this paper, the PSJ actuator is composed of a pair of tungsten electrodes and a boron nitride cavity without a cap. The cavity has a diameter of 8 mm and volume of 400 mm'. The distance between two electrodes ranges from 1 mm to 4 mm. The PSJ actuator is excited by a homemade generator CMPC-40D, output pulse parameters of which are as follows: the maximum voltage of 30 kV, the rise time of 0.5 μs, the pulse width of 8 μs, the repetition rate ranges from 0to5 kHz. Effects of pulse repetitive frequency (PRF) and air gap spacing on the discharge characteristics of a single actuator are investigated. Experimental results show that the discharge voltage increases with the increase of the gap spacing but decreases with the increase of the PRF. During the ignition time, the discharge voltage falls to zero in a few nanoseconds and the current discharge is damped sinusoidal oscillation. We observe that the energy dissipation oscillates in time, for a total discharge energy of 2 to 9.9 mJ. The energy decreases with the increase of the PRF, but it increases with the increase of the gap spacing. Furthermore, three actuators in series connection are studied. Experimental results show that synchronous discharge could be achieved for three PSJ actuators.

In this paper, we report on results from a computational investigation of nanosecond pulsed discharges in air of negative polarity using a two-dimensional fluid and fluid-Monte Carlo simulations. The computational parameters and conditions are taken from an experiment. The discharge is initiated near the cathode having a small radius of curvature and propagates towards the flat anode. The simulations are done in atmospheric pressure air with a nanosecond pulse of 120 kV amplitude in a 12 mm gap with a sharp cathode. The essential difference between discharges initiated by low- and high-energy beams of electrons originating in the vicinity of the cathode was observed. The beam of electrons with the initial energy of 20 keV was shown to result in a diffuse discharge, while the 20 eV beam had a negligible influence on the discharge evolution. By analyzing the experimental and computational results, we conclude that a diffuse discharge is formed due to fast electrons without any assumptions on the critical role of the runaway electrons. More study is required to explore the intermediate range of energies and investigate the transition to the diffuse mode of the discharge.