Experimental observations and simulation results regarding a pure He atmospheric pressure plasma jet (APPJ) and He + N 2 APPJs interacting with a downstream dielectric substrate are presented in this paper. Experiments utilizing spatialtemporal imaging show that, in the case of the pure He APPJ, an annular plasmasubstrate interaction pattern is formed. With the introduction of N 2 , the plasma is more uniformly distributed on the substrate surface, appearing a solid interaction pattern. The experimental measurements indicate 0.5% N 2 mixture is the optimal condition to achieve the most intense discharge, while the plasma substrate contact area is slightly reduced by 6.1% in comparison to that of the pure He APPJ. A 2D selfconsistent fluid model is constructed to provide insights into the role of the addition of trace of N 2 on the discharge dynamics. The discharge morphologies predicated by the model is in principle consistent with the experimental observations. The simulation reveals that the conversion from the annular plasmasubstrate interaction pattern to the solid one is attributed to the synthetic effect of the addition of N 2 and the presentence of the substrate acting as the cathode to enhance the local electric field. In the solid interaction pattern, the Penning ionization makes a significant contribution to the surface discharge, especially in the afterglow region. The dominant positive ions (N + 2 and N + 4 ) and the reactive oxygen and nitrogen species including O and N gain remarkable increment in the flux intensity to the central surface, which merits great application potential.

A systematic investigation on the dynamics and evolution mechanisms of multiple-current-pulse (MCP) behavior in homogeneous dielectric barrier discharge (HDBD) is carried out via fluid modelling. Inspecting the simulation results, two typical discharge regimes, namely the MCP-Townsend regime and MCP-glow regime, are found prevailing in MCP discharges, each with distinctive electrical and dynamic properties. Moreover, the evolution of MCP behavior with external parameters altering are illustrated and explicitly discussed. It is revealed that the discharge undergoes some different stages as external parameters vary, and the discharge in each stage follows a series of distinctive pattern in morphological characteristics and evolution trends. Among those stages, the pulse number per half cycle is perceived to observe non-monotonic variations with applied voltage amplitude (Vam) and gap width (dg) increasing, and a merging effect among pulses, mainly induced by the enhanced contribution of sinusoidal component to the total current, is considered responsible for such phenomenon. The variation of incipient discharge peak phase (Φpm) is dominated by the value of Vam as well as the proportion of total applied voltage that drops across the gas gap. Moreover, an abnormal, dramatic elevation in Jpm with dg increasing is observed, which could be evinced by the strengthened glow discharge structure and therefore enhanced space charge effect.

Detailed corrections are given as follows.1. On page 3, the term describing the power input from the electric field in equation ( 2) should read E•Γ e instead of E•Γ ε . The corrected equation is given below:2. On page 3, the sentence 'A non-linear solver PARDISO [52,53] is employed to…' should be corrected to 'A direct solver PARDISO [52,53] is employed to…'. 3. In figure 2, the correct unit of 'Time' should be 'μs' instead of 'ms'. 4. In figures 6, 8 and 9, the correct unit of 'Average reaction rate' should be 'mol 9 should be revised to: 'figure 9. The caption of figureTemporal variations of (a), (c) and (e) space-averaged electron production rates, (b), (d) and (f) space-averaged charged particle densities over one normalized applied voltage period under three different N 2 levels. The applied voltage amplitude (V am ), driving frequency (f ) and gap width (d g ) are fixed at 1.5 kV, 10 kHz and 1 mm, respectively'.

In this paper, a 2D fluid model is employed to investigate the radial evolution of the discharge structures in a helium dielectric barrier discharge with 100 ppm nitrogen impurity. By elevating the applied voltage amplitude (V am ), the discharge exhibits some distinctive radial evolution features that comprise three aspects: (1) the lateral migration of the peripheral filament, i.e. outward filament migration nearby the electrode edge; (2) the reduced intervals between two successive filaments; (3) the growth in the number of filaments. It is revealed that the radial position of the peripheral filament is basically consistent with that of the initial local intense discharge, whose location is closely related to the surface charge distribution during the initial breakdown. An increase in V am reduces the duration of the current pulse, and hence, the displacement of space charges is restrained. When more charges are restrained in the gap rather than being attached to the dielectric surfaces, the surface charge distribution becomes more uniform, which contributes to the lateral migration of the peripheral filament. Meanwhile, the lateral uniformity of Penning ionization rate is improved with V am increasing, and the seed electron level in the intervals becomes comparable to that in the filamentary channels, leading to a more uniform radial seed electron profile that attenuates the electric field distortion. As a result, the intervals between two adjacent filaments are shortened. With the lateral migration and reduced intervals as V am increases, we observe the growth in the number of filaments, and the improvement of the radial discharge uniformity.

In this paper, a two-dimensional axisymmetric fluid model was established to investigate the influence of nitrogen impurity content on the discharge pattern and the relevant discharge characteristics in an atmosphere pressure helium dielectric barrier discharge (DBD). The results indicated that when the nitrogen content was increased from 1 to 100 ppm, the discharge pattern evolved from a concentric-ring pattern into a uniform pattern, and then returned to the concentricring pattern. In this process, the discharge mode at the current peak moment transformed from glow mode into Townsend mode, and then returned to glow mode. Further analyses revealed that with the increase of impurity level, the rate of Penning ionization at the pre-ionization stage increased at first and decreased afterwards, resulting in a similar evolution pattern of seed electron level. This evolution trend was believed to be resulted from the competition between the N 2 partial pressure and the consumption rate of metastable species. Moreover, the discharge uniformity was found positively correlated with the spatial uniformity of seed electron density as well as the seed electron level. The reason for this correlation was explained by the reduction of radial electric field strength and the promotion of seed electron uniformity as pre-ionization level increases. The results obtained in this work may help better understand the pattern formation mechanism of atmospheric helium DBD under the variation of N 2 impurity level, thereby providing a possible means of regulating the discharge performance in practical application scenarios.