Simulation of electrostatic turbulence due to sheared flows parallel and transverse to the magnetic field

Abstract

Using a spatially two‐dimensional electrostatic particle simulation code, we examine the stability of a plasma equilibrium characterized by a localized transverse dc electric field and a magnetic‐field‐aligned electron drift for L ≪ Lx, where Lx is the simulation length in the x direction and L is the scale length associated with the dc electric field. It is found that the dc electric field and the field‐aligned current can together play a synergistic role to enable the excitation of electrostatic waves even when the threshold values of the field‐aligned drift and the E×B drift are individually subcritical. The simulation results indicate that a broadband turbulence is associated with such an equilibrium. This is in contrast to the current‐driven ion cyclotron instability, which is characterized by a coherent spectrum around the ion cyclotron harmonic. Further, the growing ion waves are associated with small vortices in the linear stage, which evolves to a nonlinear state dominated by larger vortices with lower frequencies.

Equilibrium structure of the plasma sheet boundary layer‐lobe interface

“…The assumed distribution functions, however, do not satisfy the Vlasov equation since the variable z is not a constant of the motion. We point out here that since the frequency of these instabilities is dependent on the Doppler shifts arising from the sheared flows, their spectrum is not sharply peaked around any one frequency but has a significant spread as illustrated by Nishikawa et al [1990] for the case of ion cyclotron-like instabilities. The guiding center variable can be readily recognized as the canonical angular momentum in the y-direction normalized by the particle mass and cyclotron frequency.…”

“…The guiding center variable can be readily recognized as the canonical angular momentum in the y-direction normalized by the particle mass and cyclotron frequency. In particular, the nonlinear stage of the ion cyclotronlike instabihties [Nishikawa et al, 1990] is known to resuit in a low-frequency y-directed (dawn-dusk) electric field. 2(b) indicates that the maximum •ue .of the electrostatic potential energy is • 2.4 • T,.…”

Velocity shear-related ion upflow in the low-altitude ionosphere

“…These waves are potential sources for ion heating (Walker et al, 1997;Amatucci et al, 1998). Another possibility is that the velocity shear can lower the threshold for fieldaligned current-driven instabilities to excite ion cyclotron waves, thereby heating the ions at low altitudes (Nishikawa et al, 1990). According to Ganguli et al (1994), the power density transferred by the instabilities to the O + ions from the convection flow is P ≈2.7×10 −4 βω J m −2 s −1 .…”

“…Simulation of electrostatic turbulence due to sheared flows transverse to the magnetic field shows that velocity shears can lower the threshold values for the field-aligned current-driven instabilities to excite electrostatic waves, thus energizing ions at lower altitudes (Ganguli et al, 1988;Nishikawa et al, 1990). Romero et al (1992) reported the occurrence of a coherent structure (vortex-like) of the electric field potential and significant resonant ion acceleration in the nonlinear evolution of lower hybrid instabilities.…”

Parallel Flow Velocity Shear Kelvin Helmholtz Instability With Ac Electric Field

“…Ganguli et al [2][3][4] show that such a situation also gives rise to instabilities. Electrostatic particle simulation has also been employed to reveal more fully the character of the instability in the ion cyclotron regime [5,6]. Pritchett and Coroniti [7,8] have carried out similar simulation for the longer wavelength electrostatic Kelvin Helmholtz instability, showing reduction of growth when the ion gyroradius becomes comparable to the shear layer thickness.…”