Investigation of an atmospheric pressure radio frequency helium planar plasma source in humid ambient air

Abstract

Atmospheric pressure radio frequency (RF) helium plasma jets operating in open air are capable of producing abundant reactive species and are widely used in biomedical applications. A planar atmospheric pressure RF plasma is studied by diagnostics and numerical modelling in this work. A novel methodology with reduced computational time and complexity is developed by converting a two-dimensional plasma fluid model into a series of one dimensional models. The numerical model reproduced the electrical characteristics and the emission spectroscopy dynamics of the discharge in good agreement with experimental measurements. Furthermore, the air influence on the kinetics of short-lived species and long-lived species is investigated numerically. It is shown that electrons are the most abundant negative species in the discharge and their density decreases with air impurities. The increasing air impurities along the discharge channel can weaken the electric field resulting in lower ionization near the outlet, and even possibly destabilizing the discharge. Reactive oxygen species are mainly present as atomic oxygen. H2O2 is produced in the gas phase through the recombination of OH radicals and destructed by collisions with He m . It is revealed that the important for biomedical applications singlet oxygen O2(a) is primarily generated by direct excitation of O2 and destructed through recombination with O(1S). The presented model can be used to study the kinetics of reactive species in atmospheric pressure RF plasma jets working in humid ambient air typical of biomedical applications.