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

Abstract

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. Compared 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.

Temporal dusty plasma afterglow: A review

“…In complex plasmas, the electric charge of the grains is obviously a key parameter. Indeed, it determines the interactions of the dust particles with the background ions and electrons and the grain-grain interactions [such as in complex plasma crystals [27,28]]. It is also fundamental in many processes, such as the ion drag force [29,30] and electric charge shielding [31].…”

Two-dimensional complex (dusty) plasma with active Janus particles

“…The experiments described in this paper were carried out in a modified Gaseous Electronics Conference (GEC) radio-frequency (rf) reference cell 32 . Plasma was pro-duced by a capacitively coupled rf discharge in argon at 13.56 MHz.…”

Dependence of ion wake characteristics on experimental conditions

“…While the additional heating can cause a crystallized monolayer to melt, it also makes it more difficult for particles initially in a fluid state to crystallize. Previous experiments have shown that for microparticle monolayers levitating in the sheath of a rf discharge at a fixed discharge power there are two threshold pressures [21][22][23]: an upper threshold, p crys , above which the monolayer always has a crystalline structure, and a lower threshold, p MCI , below which the monolayer always undergoes MCI causing the monolayer to melt. Between these two pressures, the monolayer can exist in either a crystalline or fluid state depending on the initial state when entering the intermediate pressure regime.…”

“…This point charge model for the ion wake adequately represents the system if grains remain far enough apart that the wake charge and location relative to the dust grain are constant [16]. While previous studies have used the point charge model to study MCIs [16,[20][21][22][23][24][25][26][27][28][29], the impact of changing discharge parameters, such as rf power and neutral gas pressure, on the ion wake characteristics remains largely unknown. The nonreciprocal interaction between the dust particles due to ion wakes are also related to other types of phenomena in complex plasma such the Schweigert instability in bi-layer complex plasma crystal [30][31][32][33] or the vertical pairing of dust particles [34].…”