Stability of an inhomogeneous transverse plasma flow

The stability of a magnetized plasma that includes a sheared transverse flow is analyzed by using both fluid and kinetic formalisms. In addition to the well known Kelvin–Helmholtz modes it is found that another branch of oscillation exists which can dominate the collective effects in a plasma if the magnitude of shear in the transverse flow is sufficiently strong. The source of free energy for the new branch is an inhomogeneity in the energy density caused by the velocity shear. Kelvin–Helmholtz modes, when examined with a fluid theory, are found to be robust and therefore have dominated the analysis of plasma systems with velocity shear in both laboratory and space plasmas. However, when a kinetic formalism is applied to Kelvin–Helmholtz modes it is found that these modes are strongly Landau damped especially when the ion temperature is comparable to or larger than the electron temperature. In addition, since the Kelvin–Helmholtz mode is dependent explicitly on the second derivative of the flow it is sensitive to the profile of the flow. On the other hand, the new branch is dependent on the localized nature of the flow and hence it is less sensitive to the details of the flow profile. The two branches of oscillation are compared using both fluid and kinetic theories and their regimes of dominance discussed.