Void dynamics in low pressure acetylene plasmas

We studied a capacitively coupled RF plasma with constant flow of argon and acetylene. These plasmas are able to spontaneously form dust particles under certain conditions, resulting in a cloud of particulates up to micrometer sizes levitated in the plasma. After the dust cloud has been formed, a region without dust develops. This dust-free zone is roughly shaped as an ellipsoid and is referred to as void. Concurrently, the dust particles grow in size. During its expansion the void suddenly stops growing and even shrinks, to shortly thereafter resume its expansion. We dubbed this the ‘hiccup’. The processes are periodical and reproducible. Several techniques that are time resolved (microwave cavity resonance spectroscopy, plasma impedance monitoring) and in addition spatially resolved (laser scattering, emission analysis) are used to shed light on the intriguing phenomenon. We infer the hiccup is induced by coagulation of a new batch of dust particles inside the void.