A Simple Method to Measure the Interaction Potential of Dielectric Grains in a Dusty Plasma

TL;DR

This paper introduces a minimally perturbative experimental method to measure the interaction and confining potentials between dust particles in a plasma sheath, revealing pressure-dependent charge and screening effects.

Contribution

A novel technique for non-perturbative measurement of dust particle interaction and confinement potentials in RF plasma sheaths, validated across various pressures.

Findings

Confinement potential is parabolic over a wide pressure range.

Interaction potential fits a screened Coulomb model and decreases with pressure.

Particle charge decreases with increasing pressure, matching theoretical predictions.

Abstract

A simple minimally perturbative method is introduced which provides the ability to experimentally measure both the radial confining potential and the interaction potential between two individual dust particles, levitated in the sheath of a radio-frequency (RF) argon discharge. In this technique, a single dust particle is dropped into the plasma sheath to interact with a second individual dust particle already situated at the system's equilibrium point, without introducing any external perturbation. The resulting data is analyzed using a method employing a polynomial fit to the particle displacement(s), X(t), to reduce uncertainty in calculation. Employing this technique, the horizontal confinement is shown to be parabolic over a wide range of pressures and displacements from the equilibrium point. The interaction potential is also measured and shown to be well-described by a screened Coulomb potential and to decrease with increasing pressure. Finally, the charge on the particle and the effective dust screening distance are calculated. It is shown for the first time experimentally that the charge on a particle in the sheath of an RF plasma decreases with increasing pressure, in agreement with theoretical predictions. The screening distance also decreases with increasing pressure as expected. This technique can be used for rapid determination of particle parameters in dusty plasma.