Power Spectral Density Measurements of Turbulent Plasma and Flux Rope Merger with Fast Camera

In this study, we investigate the wavenumber Power Spectral Density (PSD) of fluctuations in a linear cylindrical argon helicon plasma and flux rope mergers in the Phase Space Mapping (PHASMA) experiment at West Virginia University. Measurements are obtained with a Photron Nova-S9 fast camera. While the helicon plasma experiments exclusively used argon, flux rope merger experiments were conducted in both argon and helium. For the helicon plasma, 800 nm and 480 nm filters were applied to isolate Ar I and Ar II lines, enabling the extraction of neutral and ion dynamics, respectively. The PSD of the helicon plasma was analyzed by varying forward power (400-800 W), magnetic field strength (800-1500 G), antenna orientation (m = $\pm$1), and RF frequencies (9.5-10 MHz). Optical PSD analysis revealed strong dissipation regions with respect to wavenumber as steep as $k^{-5.7}$ in helicon plasmas and up to $k^{-7.7}$ in flux rope mergers, corresponding to ion sound scales.