Stability of two-dimensional complex plasma monolayers in asymmetric capacitively-coupled radio-frequency discharges

Lénaïc Couëdel (1, 2) , V Nosenko (3)

1 PIIM - Physique des interactions ioniques et moléculaires
2 U of S - University of Saskatchewan [Saskatoon, Canada]
3 DLR - Deutsches Zentrum für Luft- und Raumfahrt [Oberpfaffenhofen-Wessling]

In this article, the stability of a complex plasma monolayer levitating in the sheath of the powered electrode of an asymmetric capacitively coupled radio-frequency argon discharge is studied. Com- pared to earlier studies, a better integration of the experimental results and theory is achieved by operating with actual experimental control parameters such as the gas pressure and the discharge power. It is shown that for a given microparticle monolayer at a fixed discharge power there exist two threshold pressures: (i) above a specific pressure p cryst , the monolayer always crystallises; (ii) below a specific pressure p MCI , the crystalline monolayer undergoes the mode-coupling instability and the two-dimensional complex plasma crystal melts. In-between p MCI and p cryst , the microparticle monolayer can be either in the fluid phase or the crystal phase: when increasing the pressure from below p MCI , the monolayer remains in the fluid phase until it reaches p cryst at which it recrystallises; when decreasing the pressure from above p cryst , the monolayer remains in the crystalline phase until it reaches p MCI at which the mode-coupling instability is triggered and the crystal melts. A simple self-consistent sheath model is used to calculate the rf sheath profile, the microparticle charges and the microparticle resonance frequency as a function of power and background argon pressure. Combined with calculation of the lattice modes the main trends of p MCI as a function of power and background argon pressure are recovered. The threshold of the mode-coupling instability in the crystalline phase is dominated by the crossing of the longitudinal in-plane lattice mode and the out-of plane lattice mode induced by the change of the sheath profile. Ion wakes are shown to have a significant effect too.

Domaines: Physique des plasmas [physics.plasm-ph]

Lénaïc Couëdel, V Nosenko. Stability of two-dimensional complex plasma monolayers in asymmetric capacitively-coupled radio-frequency discharges. 2021. ⟨hal-03381172⟩