2-FLUID THEORY OF DRIFT-KINK INSTABILITY IN A ONE-DIMENSIONAL NEUTRALSHEET

A thin current sheet with thickness comparable to the thermal ion gyro radius possesses free energy capable of driving a number of plasma ins tabilities for its destabilization. Among these instabilities is the d rift-kink instability (DKI) unveiled through previous numerical simula tions. To advance our theoretical understanding of DKI, we formulate a two-fluid theory with finite ion and electron temperatures in a one-d imensional (Harris) current sheet to examine the linear properties of DKI. We reduce the stability analysis to solving a nonlocal eigenvalue equation. We find that the eigenvalue equation gives a number of grow ing modes with both symmetric and antisymmetric magnetic perturbations with respect to the neutral sheet. These solutions have high growth r ates, generally of the same order as their real frequencies, which are sizable fractions of the ion gyrofrequencies evaluated outside the cu rrent sheet. Near the center of the current sheet, the eigenfunction e xhibits fine spatial structures with dimensions much smaller than the ion inertial length. These structures become progressively broadened a s the ion to electron mass ratio is arbitrarily reduced. This theoreti cal result is potentially useful in assessing the impact of adopting u nrealistic ion to electron mass ratio in numerical simulations of DKI or thin current sheet stability.