Electromagnetic phenomena in granular flows in the laboratory and dusty plasmas in geophysics and astrophysics

In clouds of suspended particles (grains, droplets, ash, ice crystals, etc.), collisions electrify particles and the clouds produce significant electric potential differences over large scales. This is seen most spectacularly in the atmosphere as lightning in thunderstorms, thundersnow, dust storms, and volcanic ash plumes where multi-million-volt potential differences are produced, but it is a general phenomena in granular systems as a whole. To investigate the relative importance of particle properties (material, size, etc.) and collective phenomena (behaviors of systems at large scales not easily predicted from local dynamics) in granular and atmospheric electrification, we used several tabletop experiments that excite particle-laden flows. Various electromagnetic phenomena ensue. Measured electric fields are a result of capacitive coupling and direct charge transfer between the particles and the measurement plates. These results suggest that while particle properties do matter (as previous investigations have shown), macroscopic electrification of granular flows is relatively material agnostic and large-scale collective phenomena play a major role.