Instabilities and vortex dynamics in shear flow of magnetized plasmas

Abstract

Gradient-driven instabilities and the subsequent nonlinear evolution of generated vortices in sheared E X B flows are investigated for magnetized plasmas with and without gravity (magnetic curvature) and magnetic shear by using theory and implicit particle simulations. In the linear eigenmode analysis, the instabilities considered are the Kelvin-Helmholtz (K-H) instability and the resistive interchange instability. The presence of the shear flow can stabilize these instabilities. The dynamics of the K-H instability and the vortex dynamics can be uniformly described by the initial flow pattern with a vorticity localization parameter E. The observed growth of the K-H modes is exponential in time for linearly wIsEable modes, secular for the marginal mode, and absent until driven nonlinearly for linearly stable modes. The distance between two vortex centers experiences rapid merging while the angle 6 between the axis of the vortices and the external shear flow increases. These vortices proceed toward their overall coalescence, while shedding small-scale vortices and waves. The main features of vortex dynamics, the nonlinear coalescence and the tilt or the rotational instabilities of vortices, are shown to be given by using a low-dimension Hamiltonian representation for interacting vortex cores in the shear flow.938

Nonideal magnetohydrodynamic Kelvin–Helmholtz instability driven by the shear in the ion diamagnetic drift velocity in a high-β plasma

“…There have been many studies investigating nonideal MHD effects on the KH instability, e.g., Hall MHD studies, 5-7 hybrid MHD studies [8][9][10][11] and kinetic studies. [12][13][14] However, those studies concentrated on the EϫB driven KH instability and could not find a nonideal MHD instability. Although there is a study of a KH instability, 15 which is not driven by the E ϫB drift shear, their Hall MHD analysis is applicable only to thin current sheets, where ions are unmagnetized, and therefore their model is applicable to a parameter regime different from the present study.…”

Two-dimensional electron-magnetohydrodynamic nonlinear structures

“…Among numerous numerical experiments indicating the role of plasma vortices in the strong plasma turbulence and for the related anomalous particle and energy transport, we mention here only the classical works of the group from the University of Texas in Austin on the vortices in resistively driven driftwave, 11 ion tempera-ture gradient 12 and velocity shear driven turbulence. 13 Vortices in plasmas have been studied analytically both in the form of electrostatic disturbances corresponding to drift waves, [14][15][16][17][18] electromagnetic shear-Alfvèn-type perturbations [19][20][21] and also including microscopic effects beyond the single fluid MHD formulation, [22][23][24][25] Helicon ͑EMHD͒ vortex solutions of the type investigated in detail in the present paper were introduced in Ref. 5.…”

Multipoint observations of plasma phenomena made in space by Cluster

“…On the other hand, the slopes at the electron break in the two regions were generally steeper in the magnetosheath where the distribution peaks near −5.5 and slopes can be as steep as −7. A possible explanation of this discrepancy was suggested by Huang et al (2014) based on the differences in the (Kintner and Seyler 1985;Sundkvist et al 2005), shear flows (Tajima et al 1991;Rankin et al 1997), magnetic bubbles (Birn et al 2004), and reconnection (Matthaeus 1982;Matthaeus and Lamkin 1985;Hwang et al 2013). It was only with the launch of Cluster that the ability to measure directly local vorticity became possible (albeit only by using moments of the electron distribution function) by computing the spatial variation in the velocity within the volume defined by the Cluster spacecraft (see Sec.…”