Current density profiles in a compact dipole plasma

Abstract

This article presents current density profiles due to Lorentz and hydrodynamic forces in the presence of spatially varying plasma parameters, electrostatic field (E0→), and microwave electric field (E1→̃) obtained from experiments in a plasma confined by a dipole magnet driven at the steady state. The electric field E0→ (or E1→̃) and the pressure tensor P0¯ (or P1¯) were determined to obtain the total current density J0→ (or J1→̃) at various spatial locations employing the electrical conductivity tensor S¯DC (or S¯AC) as obtained in the previous work [Nanda et al., Phys. Plasmas 29, 062105 (2022)]. The results show that the DC density due to hydrodynamic force dominates over those due to the Lorentz force, and the converse is observed in the case of AC density. Furthermore, the DC flow due to the Lorentz force is regulated by bounce motion (along r̂ and θ̂) and grad-curvature drift (along ϕ̂), whereas E→×B→ drift controls the AC density along the three directions, where r̂, θ̂, and ϕ̂ represent unit vectors in spherical polar co-ordinates. The dominance of DC density due to Lorentz and hydrodynamic forces along r̂ and θ̂ directs the particles along the azimuthal direction by J→×B→ force. This prevents the loss of particles along the radial and polar directions, thus helping in overall plasma confinement. The work reveals interesting features of current density profiles, guided by bounce motion, magnetic drifts, and anisotropic pressure tensor, which would be beneficial for understanding current flow in laboratory and space dipole plasmas.