Analyzing the effects of magnetic shear and the safety factor on sheared boundary conditions in a gyrokinetic code*

Plasma simulations are vital for producing fusion energy due to their insight into plasma behavior that may not be obtainable by diagnostics and their ability to predict behavior in future reactors. A common coordinate system in simulations follows the magnetic field lines, resulting in flux tube simulations. Consequently, only part of the total plasma volume is simulated, emphasizing the importance of accuracy in determining the boundary conditions in the direction parallel to the magnetic field. An important geometric description used by many tokamaks is the safety factor profile, which contains information on the ratio of toroidal to poloidal magnetic flux at a given minor radius of the plasma. Magnetic shear is related to the change in safety factor with respect to minor radius, and it can affect the stability of the plasma. Gkeyll is an edge gyrokinetic code with flux tube geometry that applies a sheared boundary condition in the parallel direction of closed flux surfaces [1]. To probe the accuracy and stability of these boundary conditions, different combinations of safety factor profiles and magnetic shear values are compared in the code.

 

[1] Francisquez, M., et al. Comput. Phys. Commun. 298 (2024): 109109.