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Abstract Typical ionization waves (IWs) are observed during the propagation of nanosecond pulsed atmospheric pressure plasma jets (APPJs) with argon flow, combining both the measurement of the axial electric field (Ez) and the temporal resolved optical imaging. The movement of the luminous APPJ head is recognized as the development of the IW front, accompanied with the propagation of the peak electric field. Especially, the radial distribution of Ez transits from a central peak profile before the IW front arrives to a hollow profile after the pass of the IW front. As for the temporal Ez trend, there is a mode transition from the single‐peak feature under a low peak voltage to the double‐peak feature under a higher peak voltage, indicating the existence of both primary and secondary IWs. The effect of target conditions on the IWs in APPJs is also explored. With a metal target, no residual electric field is observed before imposing the high‐voltage pulses. However, with a dielectric target, the residual surface charges generate a background electric field in the opposite direction to that during IW propagation. In the free APPJ (with no target), on the voltage falling edge, a negative electric field drives the electron flow to compensate the positive ions left over during the forward IW propagation on the voltage rising edge.

Pulsed discharge plasma and its application is one of the promising directions in civilian areas of pulsed power technology. In order to promote the research and development of the theory and application technology for pulsed discharge plasma, in this paper, recent progress on the mechanism of nanosecond-pulse gas discharge and the characteristics and applications of typical pulsed plasma at the Institute of Electrical Engineering, Chinese Academy of Sciences is reviewed. Firstly, progress on mechanism of nanosecond-pulse discharge based on runaway electrons and measurement technology of runaway electrons is introduced. Then, the characteristics of three typical discharges, including direct-driven pulsed discharge, pulsed dielectric barrier discharge and pulsed plasma jet, are reviewed. Furthermore, typical plasma applications of pulsed plasma on surface modification and methane conversion are presented.

A needle-circular electrode structure helium plasma jet driven by microsecond pulsed power is studied. Spatially resolved emission results show that the emission intensity of He(33S1) line decreases monotonically along the axial direction, while those of N2(C3Πu), N2 + (B2 Σ+ u), and O (3p5P) reach their maxima at 3 cm, 2.6 cm, and 1.4 cm, respectively. The plasma plume of the four species shows different characteristics: The N2 emission plume; the He emission plume travels at a slower speed for only a very short distance; propagation of the O emission plume is not observed. Results of calculation of radiation fluxes emitted by positive streamers propagating along helium plasma jets are presented. It is shown, in agreement with the results of the present experiment and with other available experimental data, that the intensities of radiation of N2 + emission plume is composed of a bright head and relatively weak tail and travels a shorter distance than the N2 emission plume; the He emission plume travels at a slower speed for only a very short distance; propagation of the O emission plume is not observed. Results of calculation of radiation fluxes emitted by positive streamers propagating along helium plasma jets are presented. It is shown, in agreement with the results of the present experiment and with other available experimental data, that the intensities of radiation of N2(C3Πu) molecules and He(33S1) atoms vary with time (along the plasma jet) quite differently. The factors resulting in this difference are discussed. [ABSTRACT FROM AUTHOR]

In this paper, the uniformity of a microsecond pulse driven argon plasma jet array is studied by optimizing experimental parameters, such as the ground electrode position d, gas flow rate, and pulse frequency. The results show that when d is less than 10 mm, there are always two plasma jets that cannot be ignited; while all jets are ignited with equal length at d=12.5 mm. The plasma jet transition from laminar to turbulent at 6 l/min, presenting a "bead-like" structure. The jet length increases with the pulse repetition frequency and reaches a plateau at around 1.5 kHz. The ICCD images show that the plasma jets emerged preferably from the two quartz tubings located at the two ends of the linear array. The spatial-temporal resolved spectra show that the Ar emission (763.5 nm) and N2 emission (337.1 nm) at the end of the array (e.g., Jet #1) appeared earlier than that of the jet in the middle (e.g., Jet #2). On the contrary, the emission intensities of Ar in Jet #2 are higher than in Jet #1. This is due to the higher electric field and air diffusion at the plasma array boundary. [ABSTRACT FROM AUTHOR]

Power source is an important parameter that can affect the characteristics of atmospheric-pressure plasma jets (APPJs), because it can play a key role on the discharge characteristics and ionization process of APPJs. In this paper, the characteristics of helium APPJs sustained by both nanosecondpulse and microsecond-pulse generators are compared from the aspects of plume length, discharge current, consumption power, energy, and optical emission spectrum. Experimental results showed that the pulsed APPJ was initiated near the high-voltage electrode with a small curvature radius, and then the stable helium APPJ could be observed when the applied voltage increased. Moreover, the discharge current of the nanosecond-pulse APPJ was larger than that of the microsecond-pulse APPJ. Furthermore, although the nanosecond-pulse generator consumed less energy than the microsecond-pulse generator, longer plume length, larger instantaneous power per pulse and stronger spectral line intensity could be obtained in the nanosecond-pulse excitation case. In addition, some discussion indicated that the rise time of the applied voltage could play a prominent role on the generation of APPJs. [ABSTRACT FROM AUTHOR]

Plasma jet array is a promising device for producing low-temperature plasma at atmospheric pressure. In our letter, the effect of O2 additive on spatial uniformity of one-dimensional helium plasma jet array is described. The length of the plasma jet in the middle of the array before the injection of O2 additive is less than that on the edges of the array. However, when a small amount of O2 additive is injected into the plasma jet array, the length increases and becomes approximately the same as the length of the plasma jets on the edges of the array. The improvement of spatial uniformity of the plasma jet array is due to the enhancement of the Penning ionization in the plasma jets caused by O2 additive. Too much quantity of O2 additive, however, may lead to discharge quenching in the plasma jet array. [ABSTRACT FROM AUTHOR]

A single needle-electrode plasma jet driven by a home-made microsecond pulse power supply is studied. The electrical characteristics and optical emissions of the plasma jets driven by positive- and negative-polarity pulses are compared. With the same magnitude of applied voltage, the plasma jet driven by positive pulses shows a higher discharge current, a higher optical emission intensity and travels to a longer distance. The temporal-spatially resolved He (706.5 nm), N2 (337.1 nm) and (391.4 nm) emissions behave differently in the plasma jets driven by different polarity pulses: They appear to be discrete emission packets in the positive plasma jet, but continuous emission in the negative plasma jet (under the time resolution in this study). The emission front propagates at a faster speed in the positive plasma jet than in the negative plasma jet. The different behavior of the plasma jets is attributed to the electric field distribution under different polarity pulses. [ABSTRACT FROM AUTHOR]

In this paper, the generation and discharge modes of 2D atmospheric pressure plasma jet arrays in economic argon feeding gas with a honeycomb configuration is first reported. Two coupling and collimated discharge modes are achieved with the same array structure. The discharge modes are shown to depend on the gas flow rate and center-to-center distances of jets in the array. Stronger plasmas with higher plasma density than single jet can be obtained in coupling mode array at close proximity of jets in the array and small gas flow rate, while plasmas with moderate plasma density and relative large area can be obtained in the collimated mode array at far proximity of jets in the array. The power density and emission spectra from the centered plasma jet for the coupling mode array are both larger than those of the collimated mode. The appearance of the two discharge modes may be due to the hydrodynamic interactions between the seven individual Ar channels emerging from individual tubes with the air surrounding them. [ABSTRACT FROM AUTHOR]