This work investigates the kinetics of the N2(A3Σu +, v) state in the atmospheric pressure Townsend discharge (APTD) operated in a barrier discharge setup in pure nitrogen. To understand the complex nature of the N2(A3Σu +, v) state we have developed a detailed state-to-state vibrational kinetic model of N2 applicable mainly at low reduced electric fields (< 200 Td). The kinetic model benefits from the determination of the electric field and the electron density profile using the equivalent electric circuit analysis. The knowledge of both parameters significantly reduces the number of free parameters of the model and thus improves the accuracy of kinetic predictions. The results of the kinetic model are compared with the measured emission spectra of the second positive system and the Herman infrared system of N2. The use of the sensitivity analysis method leads to a better understanding of the role of specific elementary processes in the APTD mechanism and also to the determination of the density of the two lowest vibrational levels of N2(A3Σu +), which varies between 1012 and 1014 cm-3 depending on the applied voltage. The determination is important, because the two lowest vibrational levels of N2(A3Σu +) are considered to play an important role in the secondary emission of electrons from dielectric surfaces. This work shows that the complex state-to-state kinetic modeling in combination with the phase-resolved emission spectroscopy is the key to a better understanding of the processes responsible for establishing and sustaining the APTD mechanism in nitrogen.

We investigate the electric field development in weak microseconds-lasting atmospheric pressure Townsend discharge (APTD) operated in barrier discharge arrangement in pure nitrogen. The electric field is determined using four different methods: laser-aided EFISH (electric field induced second harmonics), optical emission- based FNS/SPS (first negative/second positive systems of molecular nitrogen) intensity ratio, electrical equivalent circuit approach and via determination of the Townsend first coefficient α(E/N) from the optical emission profile. The resulting values of the electric field obtained by the respective methods, regardless of the differences in absolute values, lie within a reasonable range. Limitations and advantages of all methods are discussed in detail for investigated discharge. The EFISH measurements are supported by re- computation of the effective interaction-path of the laser using an electrostatic model. The FNS/SPS method provides systematically higher values compared to other methods. We discuss in detail the potential origins of this discrepancy as this method is at the limit of its applicability due to the impossibility of fully verifying the underlying assumptions. The focused discussion addresses best-practice issues and identifies possible future steps to improve each of the four methods under given conditions.

Barrier discharges are known for strong memory effects which shape their stochastic properties. We study memory propagation in a surface barrier discharge operated at the water interface using electrical measurements and synchronized intensified CCD imaging. Comprehensive electrical data sets of seemingly chaotic behaviour are evaluated from thousands of subsequent periods recorded with high temporal resolution and large dynamic range. We confirm known memory effects and identify new ones both in between the half-periods as well as between subsequent pulses within one half-period. We find two memoryless states for the first discharges in the positive polarity which are defined by the presence/absence of photoemission-induced collective behaviour. Given the determined probability for entering one of these two suspected Markov states, the system bifurcates and follows one of the two subsequent non-Markovian pathways. The identification of the collective behaviour in these pathways enables us to recognize the spatially resolved property of the system and to determine its probability of occurrence solely from the zero-dimensional electrical characterisation.

We study the interaction of microplasma with viscous liquid in a narrow gap. The reduced surface tension and viscosity of the liquid droplet from local plasma-heating induce a radial fingering. The introduced methodology enables spatially and temporally resolved quantification of dissipated power density and of resulting velocity of the advancing plasma–liquid interface. For two plasma power scenarios, we demonstrate how the irregular distribution of the two parameters leads to microflow, interface stretching, and to primary droplet fragmentation via capillary instability and end pinching.