Magnetized plasma experiment on layering and inhomogeneous mixing in a fluctuating vortex array

In this work we investigate layering using a fluctuating cellular (or vortex) array which intrinsically drives inhomogeneous mixing. This is a model system for staircase dynamics and the vortex array is created in a magnetized plasma as a system of tangent eddies. This physical system has been realized in experiments carried out at the Large Plasma Device (LAPD), UCLA. To create the vortex lattice in the experiment, a smaller LaB₆ cathode source is placed at the opposite end of the device relative to the main discharge large area LaB₆ cathode. A carbon mask containing a patterned array of holes is placed in front of this smaller cathode. Two patterns have been explored; a square lattice (3x3) and concentric circular pattern. Biasing the smaller cathode to a mesh anode in front of the main discharge cathode establishes a dynamical vortex filament lattice. In the near field region of the lattice, a local plasma potential well forms which induces ExB differential rotation of the lattice resulting in azimuthally symmetric inhomogeneous boundary layers with a scale set by the initial lattice structure. A series of mixing layers is interspersed with the boundary layers and at least two transport time scales have been identified; the first is associated with fast cell (azimuthal) turnover and the second a slower cross-field diffusión in the mixing zone between the layers. The analysis is support by numerical simulations using the vorticity and continuity equations as well as more complete model BOUT++.