Intra-cavity dynamics in a microplasma channel by side-on imaging

Abstract

Abstract Here, a microplasma channel was investigated. The design was developed from a recently presented modular microplasma array. The setup consists of three stacked layers: a magnet, a dielectric foil and two nickel foils that are separated by a 120 μm wide gap. The magnet is grounded while the two nickel foils are powered. The channel is in two dimensions identical (50 μm high and 120 μm wide) to a single cavity of the microplasma arrays while it is two orders of magnitude longer. Unlike the microplasma arrays, the channel provides an additional optical access to the inside of the cavity from the side. The setup was operated with a triangular voltage with a frequency of 10 kHz and an amplitude of up to 700 V at atmospheric pressure. Phase resolved emission images were used to investigate the microplasma channel dynamics with line of sight from the top and from the side to the inside of the cavity. The top view images revealed that the discharge in the microplasma channel and the microplasma arrays behave similar. The already known asymmetric discharge behavior, the self-pulsing and the wavelike ignition was also observed in the microplasma channel. For the wavelike ignition in the channel a simple one dimensional model was proposed. With the additional side view images the asymmetric discharge behavior was examined more thoroughly. Unlike in the microplasma arrays, the discharge expands here in both half periods of the applied voltage above the upper edge of the powered electrodes. The discharge extends over a larger width in the half period, in which the potential of the upper electrodes is increasing, while it extends over a larger height in the other half period. Phase resolved images were also used to investigate the ignition phase of the discharge. The discharge ignites in the two half periods on a different height. This was explained by modeling the drift and diffusion of the charged particles between two discharge pulses. The new insights into the discharge dynamics in the microplasma channel will help to understand the behavior of the discharge in the microplasma arrays.