# Dust cluster spin in complex (dusty) plasmas

## TL;DR

This paper investigates the spontaneous rotation of dust clusters in complex plasmas, attributing it to ion wake forces and using simulations to match experimental observations, thereby diagnosing ion flow characteristics.

## Contribution

It introduces a combined experimental and simulation approach to understand dust cluster rotation driven by ion wake forces in complex plasmas.

## Key findings

- Cluster rotation depends on configuration and symmetry.
- Ion wake force induces net torque causing rotation.
- Simulation results agree with experimental rotation rates.

## Abstract

The spontaneous rotation of small dust clusters confined inside a cubical glass box in the sheath of a complex plasma was observed in experiment. Due to strong coupling between the dust particles, these clusters behave like a rigid-body where cluster rotation is contingent upon their configuration and symmetry. By evaluating the effects of distinct contributing forces, it is postulated that the rotation observed is driven by the net torque exerted on the cluster by the ion wake force. The configuration and symmetry of a cluster determines whether the net torque induced by the ion wake force is nonzero, in turn leading to cluster rotation. A COPTIC (Cartesian mesh, oblique boundary, particles and thermals in cell) simulation is employed to obtain the ion wake potential providing a theoretical model of cluster rotation which includes both the ion wake force and neutral drag and predicts rotation rates and direction in agreement with experimental results. These results are then used to diagnose the ion flow within the box.