Three-dimensional dusty plasma in a strong magnetic field: Observation of rotating dust tori

Abstract

This paper reports on the dynamics of a 3-dimensional dusty plasma in a strong magnetic field. An electrostatic potential well created by a conducting or non-conducting ring in the rf discharge confines the charged dust particles. In the absence of the magnetic field, dust grains exhibit a thermal motion about their equilibrium position. As the magnetic field crosses a threshold value (B > 0.02 T), the edge particles start to rotate and form a vortex in the vertical plane. At the same time, the central region particles either exhibit thermal motion or E→×B→ motion in the horizontal plane. At B > 0.15 T, the central region dust grains start to rotate in the opposite direction resulting in a pair of counter-rotating vortices in the vertical plane. The characteristics of the vortex pair change with increasing the strength of the magnetic field (B ∼ 0.8 T). At B > 0.8 T, the dust grains exhibit very complex motion in the rotating torus. The angular frequency variation of rotating particles indicates a differential or sheared dust rotation in a vortex. The angular frequency increases with increasing the magnetic field from 0.05 T to 0.8 T. The ion drag force and dust charge gradient along with the E-field are considered as possible energy sources for driving the edge vortex flow and central region vortex motion, respectively. The directions of rotation also confirm the different energy sources responsible for the vortex motion.

Rotational properties of annulus dusty plasma in a strong magnetic field

“…[ 38 ] In the present experiments, T e variation across the radial distance ( r ∼ 6–16 mm) is expected to be negligible. [ 25 ] Therefore, the radial variation of V f is assumed to be the V p variation at a given magnetic field strength. A cylindrical probe of length ∼2 mm and radius 0.125 mm is used to measure radial variation of V f [ 12 ] from disk edge region ( r ∼ 4 mm) to ring edge region ( r ∼ 18 mm).…”

“…It has been reported experimentally that 3D dusty plasma exhibits the vortex motion instead of azimuthal rotation in the presence of a strong magnetic field. [25] However, a 2D dust cluster always rotates in the direction of the magnetic field-induced ion flow. [19,26] To investigate the dynamics of a nearly 2D annulus dusty plasma (confined between the co-centric disk and ring) in the presence of a strong magnetic field, two types of combinations of a disk and ring are used.…”

“…One of our previous studies reports the influence of ring materials (conducting and non‐conducting) on the depth of the confining potential well in the presence of a magnetic field. [ 25 ] This is probably due to the difference of surface potentials of the materials in an rf discharge. A dip potential well is expected between the conducting co‐centric disk and ring.…”

“…They observed the inversion of rotation at lower magnetic field strength and a slow increase of the angular frequency after B > 0.1 T. Karasev et al [23] reported a rotating dust cluster and shell structure in the presence of a strong magnetic field. Apart from DC discharges, some interesting features of 3D dusty plasmas, as damping of dust-acoustic waves [24] and counter-rotating dust torus [25] have been reported in recent experiments by Choudhary et al in rf discharge. Melzer et al [26] investigated the effect of a strong magnetic field (B > 5 T) to a dust cluster confined by a ring shaped electrode in an rf discharge.…”

Comparative study of the surface potential of magnetic and non-magnetic spherical objects in a magnetized radio-frequency discharge

“…2004; Saitou & Ishihara 2013; Choudhary, Mukherjee & Bandyopadhyay 2017, 2018; Choudhary et al. 2020). In a dusty plasma, a dust particles are assumed to be spherical capacitors, which allows us to determine the surface potential and the net charge on it.…”