Absolute ozone densities in a radio-frequency driven atmospheric pressure plasma using two-beam UV-LED absorption spectroscopy and numerical simulations

T Gans,K Niemi,D Schröder,A Greb,D O’Connell,S Schröter,A Wijaikhum,J Friderich,A R Gibson,V Schulz-Von Der Gathen

doi:10.1088/1361-6595/aa8ebb

Abstract

The efficient generation of reactive oxygen species (ROS) in cold atmospheric pressure plasma jets (APPJs) is an increasingly important topic, e.g. for the treatment of temperature sensitive biological samples in the field of plasma medicine. A 13.56 MHz radio-frequency (rf) driven APPJ device operated with helium feed gas and small admixtures of oxygen (up to 1%), generating a homogeneous glow-mode plasma at low gas temperatures, was investigated. Absolute densities of ozone, one of the most prominent ROS, were measured across the 11 mm wide discharge channel by means of broadband absorption spectroscopy using the Hartley band centred at λ = 255 nm. A two-beam setup with a reference beam in Mach–Zehnder configuration is employed for improved signal-to-noise ratio allowing high-sensitivity measurements in the investigated single-pass weak-absorbance regime. The results are correlated to gas temperature measurements, deduced from the rotational temperature of the N2 (C 3 B 3, υ = 0 2) optical emission from introduced air impurities. The observed opposing trends of both quantities as a function of rf power input and oxygen admixture are analysed and explained in terms of a zero-dimensional plasma-chemical kinetics simulation. It is found that the gas temperature as well as the densities of O and O2(b) influence the absolute O3 densities when the rf power is varied.

Highlights

Introduction ce an us cri ptCold atmospheric pressure plasmas are efficient sources for the generation and controlled delivery of short- and long-lived reactive species at ambient pressure and close to roomtemperature [1,2]
The absorption setup developed in this work for ozone density measurements provides an overall fluctuation level for the unabsorbed baseline signal of about 4×10−4
This limit is mainly determined by changes in the absolute intensity of the UV-light emitting diode (LED) light source due to the instability of the corresponding current/power supply unit, rather than signal-to-noise limitations of the charge coupled device (CCD) camera used

Summary

Introduction ce an us cri pt

Cold atmospheric pressure plasmas are efficient sources for the generation and controlled delivery of short- and long-lived reactive species at ambient pressure and close to roomtemperature [1,2]. Ozone is a long-lived reactive species whose production and destruction depends on a variety of plasma-chemical reactions involving ground-state and excited oxygen atoms and molecules in the active plasma region. 2. Experimental setup us cri pt beam setup with a reference beam in Mach-Zehnder configuration for improved signalto-noise ratio allowing high-sensitivity measurements in the investigated single-pass small-absorbance regime with the capability of spatially resolved measurements. Experimental setup us cri pt beam setup with a reference beam in Mach-Zehnder configuration for improved signalto-noise ratio allowing high-sensitivity measurements in the investigated single-pass small-absorbance regime with the capability of spatially resolved measurements This technique is used to measure absolute O3 densities in the plasma core of a homogeneous. A zero-dimensional plasmachemical kinetics simulation, GlobalKin [55,56], based on the reaction mechanism given in [48], has been used to analyse the main pathways of O3 production and destruction in order to explain the trends observed experimentally

The atmospheric pressure plasma source ce

UV-broadband absorption setup and procedures ce

Global model ce

Results and Discussion ce

Conclusions pte

Acknowledgements ce