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'.

This work investigates the hydrodynamic characteristics of a coaxial double-ring electrode helium plasma jet by means of a “Z-type” Schlieren imaging system. The Schlieren images and visual optical photographs made show that a transition point from a laminar region to a turbulent region exists for gas flow without plasma when the helium flow rate exceeds a certain value. After plasma ignition, the laminar region shrinks with voltage increases, and the maximum length of the plasma plume is confined to the laminar region. The heat transfer equation and the spectral broadening of the He I 667.8 nm were used to estimate the increased gas temperature in the plasma jet, and the change in gas velocity by ionic momentum transfer was found by application of a double sphere collision model. As a result, gas heating is considered to be the dominant factor for the earlier onset of turbulence after plasma ignition, whereas the role of ion momentum transfer to neutral gas molecules is comparatively weak. The hydrodynamic behaviors of the plasma jet at the impact region for organic glass and silicon substrates are also researched. The ionization front propagates along the organic glass surface and contracts at the impact point on the silicon surface. More visible vortices are observed from Schlieren images with silicon substrates than with organic glass substrates. Possible mechanisms related to the different treatment effects are discussed.

A numerical study on the ignition properties of helium discharge confined in a dielectric tube is conducted with a fluid model. As the tube radius R increasing from 50 µm to 3 mm, the ignition voltage firstly reduces, then increases after R exceeding 1 mm. An ion sheath is formed between the discharge channel and the tube wall. The width of sheath decide whether a ring‐shape or a solid‐shape discharge morphology can be formed. Moreover, the dynamic contraction of the discharge channel is observed. Under conditions of low applied voltage and low seed electron density, the cross‐section of the discharge front is adjusted to contract to enhance the self‐built electric field, and therefore to sustain the propagation.