Dust charging and charge fluctuations in a weakly collisional radio-frequency sheath at low pressure

Abstract

Models for the charging of dust particles in the bulk plasma and in the sheath region are discussed. A new model is proposed that describes collision-enhanced ion currents in the sheath. The collisions result in a substantial reduction of the negative charge of the dust. Experimental data for the dust charge in the sheath can be described by this model when a Bi-Maxwellian electron distribution is taken into account. Expressions for the dust charging rate for all considered models are presented and their influence on the rise of the kinetic dust temperature is discussed. V C 2015 AIP Publishing LLC. [http://dx.

Effects of collision-enhanced charging on dust crystal

“…The second charging method examined here is the collision enhanced ion current model proposed by Piel and Schmidt 31 . In this model, the ion current includes the effect of collisions which can cause a flowing ion to become a thermal ion.…”

“…However, the OML model neglects charge exchange collisions which can thermalize ions that can become trapped by a negatively charged dust grain and reduce the dust grain charge. Since the collision enhanced current depends on the ion motion, there are two models that incorporate it, one for the bulk 30 where the ion velocity is low and one for the sheath 31 where the ion velocity is significant. The work by Piel and Schmidt 31 showed the effects of the collision enhanced current on the surface potential of a single dust grain, the current work examines the effects on a dust crystal.…”

“…Since the collision enhanced current depends on the ion motion, there are two models that incorporate it, one for the bulk 30 where the ion velocity is low and one for the sheath 31 where the ion velocity is significant. The work by Piel and Schmidt 31 showed the effects of the collision enhanced current on the surface potential of a single dust grain, the current work examines the effects on a dust crystal. Modeling efforts through a particle description of dust have been more interested in waves or voids 12,32 than in the structure of the plasma crystal.…”

“…The present study models a GEC cell dust experiment performed by Douglass et al 41 to gain further understanding of the dust crystal in this experiment. Further, the dust charging was separately represented by the OML approach and the collision enhanced charging (CEC) approach 31 to quantify the effect of the collision enhanced charge on the crystal. The plasma is modeled using a continuum approach illustrated in §II.…”

Nanoparticle growth by collection of ions: orbital motion limited theory and collision-enhanced collection

“…However, it was shown that even few collisions can lead to an increase of the ion current [4,5,6,7,8,9]. We here operate with a typical gas pressure of the order of 100 Pa, where the mean free path length for ions at the gas temperature is about 100 -200 µm.…”