Ion temperature dynamics for the edge and scrape-off layer plasma turbulence: role of gyro-viscosity and vorticity

In the presence of magnetic curvature and density/pressure inhomogeneity, the edge and scrape-off layer (SOL) regions of a tokamak plasma are highly turbulent mainly because of the drift/interchange instability mechanisms. The divergence of ion polarization drift contains the ion diamagnetic drift and (E) over right arrow x (B) over right arrow drift velocity to define the plasma vorticity and convection of fluid, which can be approximated in several ways using various combinations of these two drifts. Here, in this work, three different approximations are used to represent three different models and are solved numerically. The numerical results indicate that the basic results of turbulence like radial profiles, radial electric field gradients, fluctuation labels, and Reynolds stress are widely different from the three different models. As these models provide different results, therefore, one must be careful to use these approximations for the description of turbulence. This work may be useful in choosing appropriate approximations to include ion temperature gradients for the turbulence studies on tokamaks/stellarators. The role of gyro-viscosity for plasma turbulence has been identified in this work.