Rotational motion of spherical dust in plasmas with magnetic fields

The rotational dynamics of spherical, conducting dust grains in collisionless plasmas due to asymmetric momentum and current collection in the presence of a uniform magnetic field was modeled using the Monte Carlo code DiMPl. The dependence of the torque, equilibrium rotation rate, and equilibration timescale on the strength of the magnetic field and the surface potential was determined. The direction and magnitude of the rotational velocity were found to depend on the sign and magnitude of the surface potential. At a fixed positive charge, dust rotated anti-parallel to the magnetic field due to accumulation of angular momentum from electron impact while at the floating potential, dust rotated parallel to the magnetic field. This model was used to explain existing experimental observations of isolated dust grain rotation in low temperature discharges. In isothermal tokamak plasmas, equilibrium rotation rates of the order 10 5 Hz are anticipated to occur over time-scales of 20 ms which will have important consequences for dust dynamics. Published under an exclusive license by AIP Publishing.

Automated summary

The study modeled the rotational dynamics of spherical, conducting dust grains in collisionless plasmas due to asymmetric momentum and current collection in the presence of a uniform magnetic field. It found the dependence of torque, equilibrium rotation rate, and equilibration timescale on the strength of the magnetic field and the surface potential, as well as explained observed rotations of isolated dust grains in low temperature discharges.