Dispersive properties of a magnetized plasma with a field-aligned drift and inhomogeneous transverse flow

Abstract

Electrostatic fluctuations driven by the combination of a magnetic-field-aligned electron current and a localized transverse electric field are investigated. Characteristic parameters, such as scale length and magnitude of the sheared E×B velocity, magnitude of the magnetic-field-aligned current, and temperature ratio τ≡Ti/Te are varied to include conditions associated with electrostatic waves driven entirely by magnetic-field-aligned current, driven entirely by transverse electric field, and driven by a combination of magnetic-field-aligned current and transverse electric field. It is shown that, in contrast to the homogeneous case of current-driven modes, the modes in the presence of a transverse-velocity shear can be unstable in a wider range of temperature ratio τ and they are broadband in frequency. Using a simplified model, numerical solutions of the nonlocal dispersion relation, and physical arguments, cases of stabilization and destabilization due to the inhomogeneous energy-density driven instability mechanism are studied for the ion-cyclotron, ion-acoustic and drift modes. The response of the plasma to transverse-velocity shear can be categorized as reactive or dissipative and conditions corresponding to the predominance of either one are evaluated. Possible applications of these results to space and laboratory plasma are discussed.