Experiments and Modeling of Turbulence, Transport, and Flows in a Magnetized Linear Plasma Using a Global Two-Fluid Braginskii Solver

Experiments and numerical modeling of the dynamics of turbulence in the presence of flow shear are being conducted in helicon plasmas in the linear HelCat device. Modeling is being done using GBS, a 3D, global two-fluid Braginskii code that solves for plasma equilibrium as well as fluctuations. Past flow measurements have been difficult to reconcile with expectations, such as azimuthal flows being dominated by Er x Bz rotation. Therefore, recent measurements have focused on understanding plasma flows, and the role of neutral dynamics. In the model, a set of drift-reduced Braginskii equations are evolved using the GBS code. For low-field Ar plasmas a cross-field thermal collisional term must be added to shift the electric potential in the ion momentum and vorticity equations, as the ions are unmagnetized. Significant radially and axially dependent neutral profiles are also included in the simulations to try and match those observed in HelCat. Simulations show a dependence on the axial magnetic field and strong axial variations that suggest drift waves may be important in the low-field case. Recent LIF neutral profiles and off-axis plasma sourcing have been incorporated to the simulations, consistent with observations.