Stability Analysis of Low Frequency Electrostatic Modes in a Large Scale Helicon Plasma in the Presence of Sheared Flows

Experiments in the linear HelCat device, which investigate the nonlinear dynamics of edge fluctuations in the presence of varying flows affected by plasma biasing, show increasingly chaotic behavior as the bias is increased. These experiments have been conducted in a weakly turbulent regime near marginal stability. It is found that as bias is increased, flow shear penetrates into the plasma core from the edge, drift waves (DW's) suppress, and Kelvin-Helmholtz (KH) modes are excited. It is postulated that a 3-dynamical variables-type interaction between the DW, KH and the \textit{local} flow leads to chaotic behavior. Building on a linear theory by Light, \textit{et al} [Phys Plasmas \textbf{8}(10), 4675, 2001], a resonant interaction between the mode and the local flow, where mode conversion can occur, is investigated. We report on the linear stability, as well as progress on modelling the plasma with a 2D nonlinear fluid code.