Image-Based Turbulence Measurements in the PHAse Space MApping (PHASMA) Experiment

The PHAse Space MApping (PHASMA) experiment employs non-perturbative, optical diagnostics for ion velocity distribution, electron velocity distribution, magnetic field, and turbulence measurements. Here we review the design and implementation of an imaging system optimized for measurements of plasma turbulence. A Photron NOVA S9 camera provides measurements of spontaneously plasma emission at acquisition rates up to 900,000 frames per second. We describe the optical configuration used to acquire the images and the image analysis routines used to extract high contrast images that emphasize large mode number spatial structures (small scale) in the helicon source region of PHASMA. The high-contrast images are then spatially Fourier analyzed to determine the azimuthal and radial mode structure of the plasma when viewed along the background magnetic field. We report on the structure of high order azimuthal modes as a function of radial location in the plasma and as a function of background magnetic field strength. We also report on application of the same methods to reconnecting flux rope plasmas.