History of generating and controlling a radially inhomogeneous ExB velocity profile from a radially localized radial electric field in a solenoidally magnetized plasma column

Ion-cyclotron range of frequencies (ICRF) heating is highly effective in heating lab plasmas to high temperatures in toroidal devices. High-latitude ionospheric observations of thermal ion outflows (mainly O+) can be explained as resulting from ICRF-resonant heating, thus contributing to atmospheric loss from the planet. Our objective is to advance the understanding of EM waves driven by a combination of B-field-aligned current (FAC) and ExB-drift inhomogeneity (shear) that are destabilized in the ICRF. We contrast various configurations utilized in previous experiments for generating either FAC or radially inhomogeneous perpendicular-velocity shear in a magnetized plasma column, specifically, Segmented-Electrode + Single-Source (SESS), Single-Mask + Single-Source (SMSS), Single-Mask + Double-Source (SMDS), and Double-Mask + Double-Source (DMDS), and explain the cause and effect of many design features. We document the performance of these designs in terms of the radial profiles for floating potential, plasma potential, and E_r x B drift, as well as the inhomogeneity length scale, L_E, and its ratio with the ion gyroradius, ρ_i /L_E. Past experiments operated at ?? < 1e-6, whereas LAPD experiments now can operate at higher plasma beta (?? ~ 0.1) that is needed to explore EM signatures of ICRF waves.