Charging behavior of single and clustered microparticles in spatiotemporal afterglow plasmas

The charging dynamics of microparticles in plasma afterglows are critical in various scientific and technological contexts, including astrophysics, semiconductor processing, and fusion devices. While single-particle charging in steady-state plasmas is well understood, the transient behavior of aggregates in the spatiotemporal afterglow remains less explored. This work investigates the charging behavior of single and clustered microparticles (singlets, doublets, triplets, and quadruplets) within the afterglow of an inductively coupled argon plasma. High-speed imaging and trajectory analysis were used to derive particle charge through force balance considerations. To support the analyses of the charge measurements, the intensity of the 811 nm argon emission line was measured spatially resolved, providing a qualitative measure of the electron density and electron temperature. The results reveal a transition from strongly negative particle charge in the plasma bulk to near-neutral in the spatial afterglow, and to weakly positive values near the electrodes. The magnitude of the negative charge scales with cluster size, consistent with OML processes. These findings provide new experimental insight into the charging dynamics of particle aggregates under transient and non-quasi-neutral plasma conditions, relevant to dusty and complex plasma physics and plasma-assisted manufacturing.