Global three-dimensional Fluid SOL simulations with aspect ratio effects

Plasma edge turbulence plays a fundamental role in determining the performance of fusion devices. In the Scrape-Off-Layer (SOL), the plasma dynamics is the result of the interplay between the plasma outflow from the core, perpendicular transport and parallel losses at the limiter, with the high collisionality that makes possible the use of a fluid model. This work presents Scrape-Off-Layer 3D global fluid simulations using the GBS code [1], that evolves the drift-reduced Braginskii equations [2] for a collisional plasma with cold ions in open field-line geometry. Originally written using the s-α geometry, the code is now extended to a circular geometry model that retains aspect ratio effects. The basic electrostatic and electromagnetic instabilities, such as Ballooning Modes and Drift Waves, are investigated. By looking at the aspect ratio dependence of the various operators, the effects of the geometry are identified. Then, nonlinear simulations are carried out. First, some convergences studies are presented and the steady state is discussed. Second, basic characteristic of turbulence in the presence of finite aspect ratio effects are illustrated and compared with simulations where those terms are neglected. Finally, the various features of the model, such as electromagnetic perturbations, magnetic shear and self-consistent boundary conditions are discussed.