Mode Structure in Cylindrical Helicon Plasma Measurements Using a Fast Camera in the WVU PHASMA Experiment

We report the experimentally determined dispersion relations for drift waves in a helicon plasma source. The measurements are obtained optically with a Photron fast camera on the West Virginia University PHAse Space Mapping (PHASMA) experiment. Axial measurements of the cylindrical argon plasma allow for radial, angular, and temporal resolution. Assuming cylindrical symmetry we extract mode structures both inside and out of the blue core helicon plasma. Variations in mode structures as a function of forward RF power (550 – 750 W), magnetic field strength (1k – 1.5k G) and direction, fill pressure (3-3.7 mTorr), and emission wavelength (to separate ion and neutral emission contributions) are presented. Higher m mode structures are more prevalent in larger guide fields with larger forward input power within the blue core region. The helicon plasma becomes increasingly unstable at higher magnetic fields.