Reactive Species Production In Argon And Helium Plasma Jets: Reactivity Transfer From Plasma To Liquid Layers

Atmospheric pressure plasma jets are often used in plasma medicine as sources of reactive species in biomedical applications including the treatment of wounds and cancerous tumors. A rare gas or a mixture of a rare gas with a small percentage of oxygen are often used as a plasma-forming gases [1]. The biological responses are attributed to the production of reactive oxygen and nitrogen species. The reactive species generated by the plasma diffuse through a thin layer of a biological liquid which usually covers the treated sample.

In this work, we discuss results from computational investigations of properties of a single jet and jets array operated in He and Ar. We quantify densities and fluxes of reactive species produced by jets in the bulk plasma (Figure 1). We then investigate the reactivity transfer from the plasma into the liquid. As this process typically occurs on a large dynamic ranges of timescales, the plasma–liquid interactions and liquid phase chemistry are considered on a short (ns) and long (ms) time scales.

This investigation is conducted using the 2D modeling platform nonPDPSIM, which solves transport equations for charged and neutral species, Poisson’s equation for the electric potential, the electron energy conservation equation for the electron temperature and Navier–Stokes equations for the neutral gas flow. The model is essentially the same as used in [2]. The reaction mechanism includes plasma and neutral chemistry for He/humid air and Ar/humid air as well as liquid phase chemistry.

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Figure 1. (a) and (c): Flow patterns for helium and argon jet into ambient air. Numbers at the lines show helium and argon mole fraction. (b) and (d): OH radicals production during a short plasma time scale for helium and argon jet, respectively.