Cycloid motions of grains in unmagnetized dust plasma

TL;DR

This study reports the first observation of hypocycloid and epicycloid motions of irregular grains in unmagnetized dust plasma, highlighting the role of the Magnus force and initial conditions in complex grain dynamics.

Contribution

It introduces the first experimental observation of cycloid motions of irregular grains in plasma and confirms the influence of the Magnus force through comparison experiments.

Findings

Hypocycloid and epicycloid motions observed for the first time in plasma.

Magnus force from grain spin significantly affects grain motion.

Complex motions explained by force analysis and numerical simulations.

Abstract

Hypocycloid and epicycloid motions of irregular grain (pine pollen) are observed for the first time in unmagnetized dust plasma in 2D horizontal plane. Hypocycloid motions occur both inside and outside the glass ring which confines the grain. Epicycloid motion only appears outside the glass ring. Cuspate cycloid motions, circle motion, and stationary grain are also observed. All these motions are related with both the initial conditions of dropped grain and the discharge parameters. The Magnus force originated from the spin of the irregular grain is confirmed by comparison experiments with regular microspheres, and it plays important role on these (cuspate) cycloid motions. The observed complex motions are explained in term of force analysis and numerical simulations. Periodical change of the cyclotron radius as the grain travelling results in the (cuspate) cycloid motions. Our results show that the (cuspate) cycloid motions are distinctive features of irregular grain immersed in plasma.