Probing the sheat electric field using thermophoresis in dusty plasma. Part II: Experimental measurements

TL;DR

This study experimentally measures the vertical electric field in a dusty plasma sheath by analyzing dust crystal levitation and thermophoresis effects, revealing ion drag's significant role in force balance.

Contribution

It introduces an experimental method to reconstruct the sheath electric field using thermophoresis and dust charge measurements, highlighting ion drag effects.

Findings

Dust crystal levitates on the plasma side of the Bohm point.

Ion drag significantly influences vertical force balance.

Vertical electric field profile can be reconstructed from force measurements.

Abstract

A two-dimensional dust crystal levitated in the sheath of a modified Gaseous Electronics Conference (GEC) reference cell is manipulated by heating or cooling the lower electrode. The dust charge is obtained from top-view pictures of the crystal using a previously developed analytical model. By assuming a simple force balance, and measuring the radial confining force, the vertical electric field profile in the sheath is reconstructed. The dust crystal is shown to levitate on the plasma side of the Bohm point. Finally, it is shown that the ion drag plays an important role in the vertical force balance, even for large dust grains.