Spatially Resolved Spectral Measurements of EIH Waves Generated by Plasma Shear Flow Layer

Waves and instabilities generated by flows in plasmas due to the presence of mutually perpendicular electric and magnetic fields are of general relevance to the study of multiscale plasma dynamics and space physics. In particular, the waves generated by the shear in such flow profiles can have both stabilizing and destabilizing effects on the plasma depending on the shear's magnitude and scale length and may be the trigger of energy cascades. Over the years, laboratory experiments have been performed to simulate the broadband emissions from dipolarization fronts (highly compressed, Earth-ward propagating plasma sheets resulting from reconnection events) that energize the near-earth plasma environment, resulting in magnetospheric substorms. In this experiment, spatially scanned 3-axis Bdot and floating potential probes are used to conduct temporal cross-correlation measurements of fluctuations generated by the shear at the boundary of a cylindrical flow layer in a magnetized plasma column. This 3-dimensional data set is decomposed into cylindrical harmonics and analyzed using discrete Fourier transforms to isolate the 2-dimensional spatial structure of each mode and to reconstruct the dispersion relation of the excited waves. Since the shear layer length scale is sub-Larmor radius and the plasma skin depth to wavelength ratio transitions from less than to greater than unity, these results are compared to the non-local electrostatic and electromagnetic theory for Electron-Ion Hybrid (EIH) waves. It is shown that, in accordance with theory, the modes excited are broadly distributed around m=3 and that the waves primarily propagate in the direction of the cross-field flow.