A dust vortex is a common phenomenon in the chip etching process and microgravity-and ground-based dusty plasma experiments.Therefore,it is of great significance to study the dust-vortex formation mechanism,which remains unclear due to difficulties in determining plasma parameters in the sheath where the charged dust particles reside.In this work,we observed the motion of a single dust vortex in a new experiment on dusty plasma ratchets and studied its motion patterns under various discharge conditions.By establishing a three-dimensional dusty plasma ratchet model,we numerically investigated the distribution characteristics of the plasma parameters in the saw channel and reproduced the observed experimental phenomenon in a Langevin simulation.The experimental and simulation results revealed asymmetry in the potential distribution within the saw channel wherein dust particles are suspended,resulting in a nonzero ion flow vorticity in the sawtooth.This nonequilibrium ion drag is the fundamental force driving the dust particles to generate the vortex motion.
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