Instabilities in a current sheet with plasma jet

TL;DR

This study investigates the stability of magnetohydrodynamic current sheets with plasma jets, analyzing how different flow orientations affect instabilities and identifying conditions that stabilize or transition various modes.

Contribution

It provides a generalized stability analysis for current sheets with plasma jets, revealing how flow direction and resistivity influence mode stabilization and transition.

Findings

Streaming kink mode stabilized at V0/B0 ≲ 2

Streaming sausage mode stabilized at V0/B0 ≲ 1

Streaming tearing mode has higher growth rate with finite resistivity

Abstract

We study the stability problem of a magnetohydrodynamic current sheet with the presence of a plasma jet. The flow direction is perpendicular to the normal of the current sheet and we analyze two cases: (1) The flow is along the anti-parallel component of the magnetic field; (2) The flow is perpendicular to the anti-parallel component of the magnetic field. A generalized equation set with the condition of incompressibility is derived and solved as a boundary-value-problem. For the first case, we show that, the streaming kink mode is stabilized by the magnetic field at $V_0/B_0 \lesssim 2$, where $V_0$ and $B_0$ are the jet speed and upstream Alfv\'en speed, and it is not affected by resistivity significantly. The streaming sausage mode is stabilized at $V_0/B_0 \lesssim 1$, and it can transit to the streaming tearing mode with a finite resistivity. The streaming tearing mode has larger growth rate than the pure tearing mode, though the scaling relation between the maximum growth rate and the Lundquist number remains unchanged. When the jet is perpendicular to the anti-parallel component of the magnetic field, the most unstable sausage mode is usually perpendicular (wave vector along the jet) without a guide field. But with a finite guide field, the most unstable sausage mode can be oblique, depending on the jet speed and guide field strength.