OH in the effluent of the COST-Jet in humid environment by laser-induced fluorescence

The surrounding atmosphere of atmospheric pressure plasma jets has crucial impact on the reactive species in the effluent region. In particular, the diffusion of humid ambient air into the effluent may significantly change its plasma chemical properties. Moreover, humidity is also added by water impurities in the feed gas of the jet. By measuring the distribution of the tracer molecule OH in the jet effluent under controlled atmosphere, conclusions about the production channels of OH can be drawn. This was done by laser-induced fluorescence (LIF) in the exit region of a COST-Jet. To ensure a controlled humid environment, the COST-Jet was installed in a closed vessel, which allows to control the composition of the surrounding atmosphere. To investigate the influence of humid environment on the OH density, the humidity inside the vessel was systematically varied. In addition to the spatial distribution of OH, the measured lifetimes also provide valuable information about the ongoing processes in the jet effluent.