The spatial density distribution of H<sub>2</sub>O<sub>2</sub> in the effluent of the COST-Jet and the kINPen-sci operated with a humidified helium feed gas
B. Harris, L. Krös, A S C Nave, E. Wagenaars, J. H. van Helden
Abstract
Abstract Cold atmospheric plasma jets operated with a helium feed gas containing small admixtures of water vapour are excellent sources of H 2 O 2 for direct biomedical applications. However, H 2 O 2 is typically distributed non-uniformly throughout the effluent region, meaning the dosage received by a patient or substrate is dependent on their positioning relative to the plasma source. This study presents the spatial distribution of absolute H 2 O 2 number densities in the effluent of two popular plasma jets, the COST-Jet and the kINPen-sci plasma jet, when operated with a humidified helium feed gas. The measurements were performed using continuous wave cavity ring-down spectroscopy with a tunable, mid-infrared laser. The H 2 O 2 number density measured close to the jet nozzle is 2.3 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>×</mml:mo> <mml:mrow/> </mml:math> 10 14 cm −3 for the kINPen-sci plasma jet and 1.4 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>×</mml:mo> <mml:mrow/> </mml:math> 10 14 cm −3 for the COST-Jet. The average number density of H 2 O 2 in the effluent of the kINPen-sci plasma jet is a factor of two higher than in the effluent of the COST-Jet. The distribution of H 2 O 2 in the COST-Jet effluent is initially highly uniform and suggests negligible mixing of H 2 O 2 with the ambient air up to 15 mm from the jet nozzle, although it is rapidly diluted at further distances. In the case of the kINPen-sci plasma jet, the number density of H 2 O 2 has a more pronounced radial distribution close to the nozzle, while the mixing with the ambient air is more gradual at further distances from the nozzle. It is evident that a detailed understanding of the H 2 O 2 production in the plasma source, as well as of the transport of H 2 O 2 to the substrate through the effluent, is required in order to optimise the intended effects. This work serves to highlight the difference of the distinct spatial distribution of H 2 O 2 in the effluent of both types of plasma jets when considering their direct application in biomedicine.