Observation of Ω mode electron heating in dusty argon radio frequency discharges

Abstract

The time-resolved emission of argon atoms in a dusty plasma has been measured with phase-resolved optical emission spectroscopy using an intensified charge-coupled device camera. For that purpose, three-dimensional dust clouds have been confined in a capacitively coupled rf argon discharge with the help of thermophoretic levitation. While electrons are exclusively heated by the expanding sheath (α mode) in the dust-free case, electron heating takes place in the entire plasma bulk when the discharge volume is filled with dust particles. Such a behavior is known as Ω mode, first observed in electronegative plasmas. Furthermore, particle-in-cell simulations have been carried out, which reproduce the trends of the experimental findings. These simulations support previous numerical models showing that the enhanced atomic emission in the plasma can be attributed to a bulk electric field, which is mainly caused by the reduced electrical conductivity due to electron depletion.

Capacitively coupled rf discharge with a large amount of microparticles: Spatiotemporal emission pattern and microparticle arrangement

“…Following previous studies [18,19], the emission pattern was analyzed for the argon lines 750.4 nm and 751.5 nm. These lines correspond to the transitions 2p 1 → 1s 2 and 2p 5 → 1s 4 (in Paschen notation) with lifetimes 22.5 ns and 24.9 ns, respectively [25].…”

“…In recent years, this interaction has been studied both experimentally and using numerical simulations in several works [16][17][18][19]. Experimentally, the deepest insight into the plasma kinetics can be achieved by rf-periodresolved emission measurements.…”

“…Both rf-period-resolved measurements and PIC simulations were combined in Refs. [18,19] for the conditions of complex plasmas.…”

“…In fact, the simulations of Ref. [19] were performed for a prescribed fixed distribution of the microparticle number density. The presence of the void in the center of the discharge was not taken into account, whereas (as already mentioned above) lack of the fundamental understanding of the void constitutes a major obstacle in the improvement of microgravity plasma experiments.…”

“…[19], large microparticle clouds occupying the most part of the discharge volume were considered. It has been shown that the increase in the microparticle number density causes the transition in the electron heating mode.…”