EFFECTS OF PERPENDICULAR SHEAR SUPERPOSITION AND HYBRID IONS INTRODUCTION ON PARALLEL SHEAR DRIVEN PLASMA INSTABILITIES

Abstract

Parallel and perpendicular plasma flow velocity shears are independently controlled and superimposed in fully-ionized collisionless magnetized plasmas using a modified plasma-synthesis method with concentrically three-segmented electron and ion emitters. The fluctuation amplitude of the drift wave which has an azimuthal mode number m = 3 is observed to increase with increasing the parallel shear strength in the absence of the perpendicular shear. When the perpendicular shear is superimposed on the parallel shear, the drift wave of m = 3 changes into that of m = 2. Furthermore, the parallel shear strength required for the excitation of the drift wave becomes large with a decrease in the azimuthal mode number. Introduction of hybrid ions, i.e., superposition of two kinds of positive ions, is found to cause unexpected stabilization of the drift wave.