Abstract
Cold atmospheric pressure plasma jets make important contributions to a range of fields, such as materials processing and plasma medicine. In order to optimise the effect of those plasma sources, a detailed understanding of the chemical reaction networks is pivotal. However, the small diameter of plasma jets makes diagnostics challenging. A promising approach to obtain absolute number densities is the utilisation of cavity-enhanced absorption spectroscopy methods, by which line-of-sight averaged densities are determined. Here, we present first measurements on how the spatial distribution of HO2 in the effluent of a cold atmospheric pressure plasma jet can be obtained by cavity ring-down spectroscopy in an efficient way. Instead of recording fully wavelength resolved spectra, we will demonstrate that it is sufficient to measure the absorption coefficient at two wavelengths, corresponding to the laser being on and off the molecular resonance. By sampling the effluent from the 1.6 mm diameter nozzle in the radial direction at various axial positions, we determined that the distances over which the HO2 density was distributed were (3.9 ± 0.5) mm and (6.7 ± 0.1) mm at a distance of 2 mm and 10 mm below the nozzle of the plasma jet, respectively. We performed an Abel inversion in order to obtain the spatial distribution of HO2 that is presented along the symmetry axis of the effluent. Based on that localised density, which was (4.8 ± 0.6) ⋅ 1014 cm−3 at the maximum, we will discuss the importance of the plasma zone for the production of HO2.
Highlights
With the development of cold atmospheric pressure plasma jets (CAPJs) over the last decade, the localised and selective treatment of heat sensitive objects and biological tissue has gained high industrial and medical importance thereby widening established fields, such as materials processing, and opening new fields, such as plasma medicine and plasma agriculture [1,2,3,4,5]
We present first measurements on how the spatial distribution of HO2 in the effluent of a cold atmospheric pressure plasma jet can be obtained by cavity ring-down spectroscopy in an efficient way
It is essential to diagnose the fluxes of the plasma generated species and to identify the relevant reaction pathways which occur under different conditions, such as feed gas and surrounding gas compositions, in order to obtain a detailed understanding of the chemical reaction network and to be able to tailor the reactive species composition for a specific application
Summary
With the development of cold atmospheric pressure plasma jets (CAPJs) over the last decade, the localised and selective treatment of heat sensitive objects and biological tissue has gained high industrial and medical importance thereby widening established fields, such as materials processing, and opening new fields, such as plasma medicine and plasma agriculture [1,2,3,4,5]. It is essential to diagnose the fluxes of the plasma generated species and to identify the relevant reaction pathways which occur under different conditions, such as feed gas and surrounding gas compositions, in order to obtain a detailed understanding of the chemical reaction network and to be able to tailor the reactive species composition for a specific application. By changing the surrounding gas composition, a mixture of oxygen and nitrogen, the ozone density increased, whereas the number of reactive oxygen–nitrogen species (RONS) decreased with rising oxygen concentration in the surrounding atmosphere. These are important observations, as RONS seem to play an important role in the plasma-driven effects on biological tissue [15,16,17]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
