3-dimensional density distributions of NO in the effluent of a micro atmospheric pressure plasma jet operated in He/N2/O2 mixture *

Plasma jets are known to generate a huge number of different reactive species. In that context Nitric Oxide (NO) is one of the key players, as it triggers many biological processes and it is also considered the only radical that is stable enough to act as an extracellular messenger.  In this study absolute ground state densities of NO are measured in the effluent of an RF-driven micro atmospheric pressure plasma jet (µAPPJ), that is operated in a He/N2/O2 mixture,  by means of Laser Induced Fluorescence (LIF), with three-dimensional spatial resolution. The densities are measured in two distinct atmospheres. In the first one, the jet is expanding into open air, whereas in the second configuration the jet is expanding into a controlled He/ synthetic air mixture. From the time resolved LIF signals the quenching coefficients for He, air, N2 and O2 are determined, as well as the intrusion of the ambient air into the He gas flow expanding from the jet. It was found that the distribution as well as the absolute densities strongly depend on the surrounding atmosphere, due to quenching and collisions. Furthermore, the NO particles are strongly coupled to the He flow of the feed gas. Parameter studies, varying different parameters such as plasma power, gas flow and gas mixture have been performed and the influence on the absolute NO densities as well as its distributions are investigated.