Particle image velocimetry, laser‐induced fluorescence, and computational modeling are used to quantify the impact of plasma generation on air entrainment into a helium plasma jet. It is demonstrated that discharge generation yields a minor increase in the exit velocity of the gas. In contrast, the laminar to turbulent transition point is strongly affected, attributed to an increase in plasma‐induced perturbations within the jet shear layer. The temporal decay of laser‐induced fluorescence from OH is used as an indicator of humid air within the plasma. The results show that plasma‐induced perturbations increase the quenching rate of the OH‐fluorescent state; indicating that shear‐layer instabilities play a major role in determining the physicochemical characteristics of the plasma.

The reactive chemical species generated by non-equilibrium plasma under atmospheric pressure conditions are key enablers for many emerging applications spanning the fields of biomedicine, manufacturing and agriculture. Despite showing great application potential, insight in to the underpinning reactive species generation and transport mechanisms remains scarce. This contribution focuses on the spatiotemporal behaviour of reactive nitrogen species (RNS) created and transported by an atmospheric pressure air surface barrier discharge (SBD) using both laser induced fluorescence and particle imaging velocimetry measurements combined with experimentally validated numerical modelling. It was observed that highly reactive species such as N are confined to the discharge region while less reactive species such as NO, NO₂ and N₂O closely followed the induced flow. The concentration of key RNS was found to be in the 10–100 ppm range at a position of 25 mm downstream of the discharge region. A close agreement between the experimental and computational results was achieved and the findings provide a valuable insight in to the role of electrohydrodynamic forces in dictating the spatiotemporal distribution of reactive chemical species beyond the plasma generation region, which is ultimately a key contributor towards downstream treatment uniformity and application efficacy.

This paper reports on a numerical study of the transport of reactive chemical species generated in an atmospheric-pressure air plasma discharge under the influence of a high velocity flowing gas. Using a 1D air plasma model, it is shown that the reactive species transported downstream of the discharge region can be categorized into three distinct groups based on their spatial distribution: (i) decaying downstream species, (ii) increasing downstream species and (iii) variable density species, where the density is a function of both spatial position and gas flow velocity. It is demonstrated that the gas flow velocity influences the dominant chemical reactions downstream of the discharge region, noticeably altering the composition of several key reactive chemical species transported to a given downstream location. As many emerging applications of atmospheric pressure plasma are driven by the flux of reactive chemical species, this study highlights the importance of gas flow velocity, not only as a means to enhance mass transport but also as a means to manipulate the very nature of the reactive plasma chemistry arriving at a given location.

Using a time-dependent two-dimensional axisymmetric fluid model the interaction of a plasma jet with a dielectric surface has been studied. The model is solved for two consecutive periods of a positive unipolar pulsed waveform. The study concentrates on determining the fluxes of the main oxygen ion species, , and the total accumulated charge on the surface. Approaching the dielectric surface, the streamer head is seen to divert its direction of propagation, spreading out radially approximately 0.2 mm above the dielectric surface. For generated near the streamer head, this leads to a maximum in their flux to the surface which moves radially outwards with the streamer propagation, driven by the applied electric field in pulse on-time. In the off-time, the flux of drops by at least two orders of magnitude. As a result, the total number of ions arriving at the surface over one entire pulse period (fluence) has an annular shape limited by the effective contact area of the streamer on the surface. In contrast ions generated in the pulse on-time do not reach the surface due to the direction of the applied electric field. In the off-time, ions generated at the edges of the deformed streamer are pushed by the accumulated surface charge outwards. As a result, the fluence has an annular structure with its maximum being outside the area of the dielectric surface covered by the plasma channel. Solving for the second pulse period shows small changes in the predicted fluences, with largest difference seen with . We see that increasing the flow rate (by a factor of three) shifts the position of the maximum fluence of outwards, and decreasing the fluence in the second pulse period.

Plasma-based nanoparticle synthesis techniques are attractive in many respects but suffer from a major drawback—low productivity. We demonstrate a technique by which the growth rate of copper nanoparticles has been substantially increased by collection of copper ions. A growth rate as high as 470 nm/s was obtained as compared to a growth rate of less than 3 nm/s in the case of growth by neutrals. The increased trapping of copper is explained as orbital motion limited (OML) collection of ions. Experimentally obtained nanoparticle growth rates are in good agreement with theoretical estimates of the OML ion collection rates.