Evolution of Ion Wake Characteristics with Experimental Conditions

TL;DR

This study uses molecular dynamics simulations to explore how ion wake characteristics in plasma crystals depend on experimental conditions, revealing a strong dependence on pressure but not on power.

Contribution

It provides the first detailed analysis of how discharge pressure influences ion wake properties in plasma crystals using self-consistent simulations.

Findings

Ion wake strength varies significantly with pressure.

Discharge power has minimal effect on ion wake characteristics.

Ion wake influences mode-coupling instability in plasma crystals.

Abstract

Two-dimensional microparticle crystals can be formed in the sheath of a gas discharge plasma. Ions from the bulk plasma are accelerated in the sheath electric field, flowing past the grains to create a positive ion wake downstream from the grains. Interaction between the ion wake and neighboring grains creates additional coupling between oscillation modes and can trigger mode-coupling instability (MCI). Recent experiments have shown that at a fixed discharge power there are threshold pressures above and below which the monolayer always crystallizes or melts, respectively. The melting is due to MCI being triggered in the crystal monolayer, while the crystallization is due to the suppression of MCI by neutral damping in the fluid monolayer. The relationship between the discharge parameters and ion wake characteristics is unknown. A molecular dynamics simulation of ion dynamics and dust charging is used to self-consistently determine the dust charge and ion wake characteristics for different experimental conditions. It is found that the ion wake is strongly dependent on discharge pressure but not affected much by the discharge power.