Equation of state of a granular gas homogeneously driven by particle rotations

TL;DR

This study experimentally investigates a homogeneously driven granular gas of magnetic particles, revealing an equation of state similar to ideal gases and exponential velocity distribution tails, driven solely by rotational forcing.

Contribution

It introduces a novel experimental setup with homogeneous rotational forcing, differing from boundary-driven systems, and provides insights into the equation of state and collision statistics of such systems.

Findings

Equation of state similar to ideal gas with a geometric factor

Velocity distribution exhibits exponential tails

Homogeneous rotational forcing prevents clustering

Abstract

We report an experimental study of a dilute "gas" of magnetic particles subjected to a vertical alternating magnetic field in a 3D container. Due to the torque exerted by the field on the magnetic moment of each particle, a spatially homogeneous and chaotic forcing is reached where only rotational motions are driven. This forcing differs significantly from boundary-driven systems used in most previous experimental studies on non equilibrium dissipative granular gases. Here, no cluster formation occurs, and the equation of state displays strong analogy with the usual gas one apart from a geometric factor. Collision statistics is also measured and shows an exponential tail for the particle velocity distribution. Most of these observations are well explained by a simple model which uncovers out-of-equilibrium systems undergoing uniform "heating".