Laboratory Investigation of the Dynamics of Shear Flows in a Plasma Boundary Layer*

For a wide variety of laboratory and space plasma environments, theoretical predictions state that plasmas are unstable to transverse and parallel inhomogeneous flows over a very broad frequency range. Specifically, for a velocity shear oriented perpendicular to a uniform background magnetic field, the shear scale length ($L_{E})$ compared to the ion gyro-radius ($\rho_{i})$ determines the character of the shear driven instability that may prevail. An interpenetrating plasma configuration is used to create a transverse velocity shear profile in a magnetized plasma column. For the first time, the continuous variation of $\rho_{i}$/$L_{E}$, and the associated transition of the instability regimes driven by the shear flow mechanism, is demonstrated in a single laboratory experiment under identical plasma conditions. This work characterizes the compression/relaxation of boundary layers often generated in a variety of space plasma processes.