# The nonmodal kinetic theory for the electrostatic instabilities of a plasma with a sheared Hall current

## TL;DR

This paper develops a kinetic non-modal theory for electrostatic instabilities in Hall plasmas with sheared currents, revealing how shear influences the growth and evolution of instabilities over time.

## Contribution

It introduces a non-modal kinetic framework for analyzing plasma instabilities driven by sheared Hall currents, incorporating Doppler effects and time-dependent wave number evolution.

## Key findings

- Sheared current velocity causes nonmodal instability growth.
- Doppler-shifted modes are key in plasma component interactions.
- Instability growth rate increases as (t - t0)^3 over time.

## Abstract

The kinetic theory for the instabilities driven by the Hall current with a sheared current velocity, which has the method of the shearing modes or the so-called non-modal approach as its foundation, is developed. The developed theory predicts that in the Hall plasma with the inhomogeneous electric field, the separate spatial Fourier mode of the perturbations is determined in the frame convected with one of the plasma components. Because of the different shearing of the ion and electron flows in the Hall plasma, this mode is perceived by the second component as the Doppler-shifted continuously sheared mode with time-dependent wave numbers. Due to this effect, the interaction of the plasma components forms the nonmodal time-dependent process, which should be investigated as the initial value problem. The developed approach is applied to the solutions of the linear initial value problems for the hydrodynamic modified two-stream instability and the kinetic ion-sound instability of the plasma with a sheared Hall current with a uniform velocity shear. These solutions reveal that the uniform part of the current velocity is responsible for the modal evolution of the instability, whereas the current velocity shear is the source of the development of the nonmodal instability with exponent growing with time as $\sim\left(t-t_0\right)^3$.