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

International audienceThe 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 lambda = 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 {{{\Pi }}}u \to B 3 {{{\Pi }}}g , upsilo = 0 \to 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{}1{{{Sigma }}}g ) influence the absolute O3 densities when the rf power is varied

Plasma–liquid interactions: a review and roadmap

Plasma–liquid interactions represent a growing interdisciplinary area of research involving plasma science, fluid dynamics, heat and mass transfer, photolysis, multiphase chemistry and aerosol science. This review provides an assessment of the state-of-the-art of this multidisciplinary area and identifies the key research challenges. The developments in diagnostics, modeling and further extensions of cross section and reaction rate databases that are necessary to address these challenges are discussed. The review focusses on non-equilibrium plasmas

Time Resolved Diagnostics for Kinetic Studies in N2_{2}/O2_{2} Pulsed rf Discharges

Time resolved optical diagnostics have been applied to the study of energy transfers in N$_{2}$/O$_{2}$ pulsed radio-frequency discharge. N$_{2}$(A$^{3}\Sigma^{+}_{\rm u}$ and NO(X$^{2}\Pi$) have been measured by Laser Induced Fluorescence, and NO-$\gamma$ band by Emission Spectroscopy. The analysis in discharge and post discharge as a function of O$_{2}$ percentage allows to guess the main mechanisms correlating the relaxation of these species in the post-discharge. NO-$\gamma$ bands in N$_{2}$/O$_{2}$ discharge are mainly excited by N$_{2}$(A) + NO(X) collisions. The decay rates of N$_{2}$(A) can be accounted for by O, NO and O$_{2}$ quenching. NO ground state density, measured by LIF, varies with O$_{2}$ percentages showing a bell shape profile with a broad maximum. Some EEDF measured by Langmuir probe under continuous discharge conditions show that O$_{2}$ addition, even in few percents, strongly reduces the density of low energy electrons