The effect of the electron κ-distribution on the dust particle charging in the radio-frequency thermal-sheaths

Abstract

In order to investigate collisionless radiofrequency plasma sheaths
containing dust particles, three models are utilized:
the novel kinetic scheme. Ensemble-in-Spacetime (EST) model for calculating sheath parameters, the Dust
Particle Charging model, and the Single Dust Particle model. The EST model has
been modified to account for κ-electron distributions.
This model is applicable to radiofrequency plasma sheaths found in tokamaks equipped with an ion cyclotron
radiofrequency (ICRF) wave heating system, such as JET, West(Tore Supra), EAST,
ASDEX-U, and KSTAR. The calculated sheath parameters are utilized to determine
the electron and ion currents of the dust particles. In the intermediate radio-frequency
regime, when the ion plasma frequency is comparable to the ICRF, the flux and energy
of the ions are modulated in time within the sheath. The ions are not inertialess, and
the value of κ affects the electron and ion densities.
As the value of κ increases, the time-averaged electron and ion densities, sheath edge position, and area of the
sheath voltage-sheath charge hysteresis loop also increase. However, the ion energy
distribution remains insensitive to the κ distribution. The dust particles are charged
with different negative charges based on their radius, position within the sheath, κ-
electron distribution, and sheath potential. These particles exhibit oscillatory motion
due to their interactions with the plasma and gravitational fields and are accelerated
toward the plasma core.