Hydrodynamic and kinetic modelling of complex radio-frequency plasmas

Abstract

In this paper hydrodynamic and kinetic approaches to model low-pressure capacitively coupled complex radio-frequency discharges are discussed and applied to discharges under micro-gravity. Complex plasmas contain dust grains with a large negative charge and are characterized by a strong coupling between the properties of the plasma and those of the dust grains. After a discussion of the physics and methods involved, examples are presented from modelling of experiments under micro-gravity in the PKE-Nefedov reactor on board the International Space Station. These discharges are simulated with a 2D cylindrically symmetric hydrodynamic model.Kinetic effects are studied with a 1D particle-in-cell plus Monte Carlo model in which capture and scattering by dust grains is included. Since experiments are often performed at low pressures, the electron energy distribution function is no longer determined by the local plasma properties. This has consequences for the charging of the dust. Results of simulations with this model are compared with the hydrodynamic results. In addition, we address the behaviour of the dust charge in decaying plasmas.

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

“…[28]. The microparticles were treated as a fluid within the drift-diffusion model considered previously in a number of works [29][30][31][32][33]. The details of the model for each component are given below.…”

Threshold Phenomena in a Throbbing Complex Plasma

“…Interestingly, it can also give birth to a dust-free region near the plasma center. This void [10][11][12][13][14][15][16][17][18][19][20][21] is sustained by an equilibrium between an outward ion drag force and an inward electric force [11]. An accurate understanding of this region is of major interest as its existence is a serious issue for both theory and applications.…”

“…It is the opposite situation to what is observed when the ionization rate is enhanced by, for example, increasing the power. This usually leads to an increase in the void size [17,21,27]. But, by increasing the power (through the electrodes) we certainly change the plasma in a global way.…”

Physical aspects of dust–plasma interactions

“…The early works were examined by comparing the dimensions and onset of the void formation in the simulations and the experiments without validation of the obtained background plasma conditions. Even the development of PIC codes [ 63,277 ] with a more thorough treatment of the electron kinetics did not lead to an immediate breakthrough. The first attempt [ 65 ] to compare the outcome of the PIC simulations with the microparticle arrangement and the rf PROES‐measured spatiotemporal emission patterns in the experiment was unsuccessful in the sense of void problem, since in the simulations, “the sharp dust density gradients at the void edges resulted in unwanted boundary effects.” Another PIC model [ 66 ] was able to qualitatively reproduce the spatiotemporal emission pattern, but was unable to reproduce the formation of void.…”