Numerical study of the influence of surface reaction probabilities on reactive species in an rf atmospheric pressure plasma containing humidity

Abstract

The quantification and control of reactive species (RS) in atmospheric pressure plasmas (APPs) is of great interest for their technological applications, in particular in biomedicine. Of key importance in simulating the densities of these species are fundamental data on their production and destruction. In particular, data concerning particle-surface reaction probabilities in APPs are scarce, with most of these probabilities measured in low-pressure systems. In this work, the role of surface reaction probabilities, γ, of reactive neutral species (H, O and OH) on neutral particle densities in a He-H 2 O radio-frequency micro APP jet (COST-mAPPJ) are investigated using a global model. It is found that the choice of γ, particularly for low-mass species having large diffusivities, such as H, can change computed species densities significantly. The importance of γ even at elevated pressures offers potential for tailoring the RS composition of atmospheric pressure microplasmas by choosing different wall materials or plasma geometries.

Chemical kinetics in an atmospheric pressure helium plasma containing humidity

“…Particularly at higher H 2 O content, this is a result of OH being primarily produced by direct electron impact dissociation of H 2 O in a one step process (eqn (14)) and is consumed in interactions with other OH molecules. Atomic hydrogen behaves similarly, being produced mainly by electron impact dissociation and consumed via interactions with surfaces, 71 both of which occur relatively quickly. However, other species do not reach a steady state within the length of the plasma channel, and instead continuously increase in density up to the outlet of the plasma source.…”

“…A detailed discussion of the role of surface interactions in a similar simulation system is given elsewhere. 71 …”

Molecular admixtures and impurities in atmospheric pressure plasma jets

“…Wall recombination of H was the dominant source of H 2 at 1 μs, though several electron impact and recombination processes also generate H 2 . The importance of wall recombination reactions in humid He plasma chemistry was investigated by Schröter et al 17 As the H 2 O admixture increased beyond 0.1%, the H was selectively generated outside of the tube by the more deeply penetrating IW, where it rapidly reacted with O 2 to form HO 2 .…”

“…Schröter et al used a global model to study a humid He radio-frequency APPJ, showing a decrease in the electron density and an increase in nearly all reactive oxygen species with an increase in the H 2 O admixture. 17 Admixtures have also been shown to change the biological outcomes in applications of APPJs. In experiments by Joh et al, an O 2 admixture in a helium APPJ increased plasma-induced apoptosis in cancer cells.…”

Numerical simulation of the effect of water admixtures on the evolution of a helium/dry air discharge

“…These models are computationally efficient, but have limitations, as they do not consider the spatial evolution (diffusion and convective transport) of the different species in the mixture. The effect of water admixtures on helium discharges through global models has been investigated by several researchers [35][36][37][38][39][40]. Particularly, Liu et al [38] investigated the plasma chemistry of a He/H2O mixture.…”