Effects of superimposed parallel and perpendicular flow velocity shears on drift-wave instabilities in magnetized plasmas

Plasma flow velocity shears parallel and perpendicular to magnetic field lines are independently controlled and superimposed 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 is found to change 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. Based on these results, the superposition of the parallel and perpendicular shears can affect the characteristics of the drift wave through the variation of the azimuthal mode number. (author)