Non-axisymmetric boundary plasma modeling

This work presents two three-dimensional boundary plasma transport models employing two different approaches. The first model incorporates resonant magnetic perturbations (RMPs) effects in tokamak boundary simulations. Calculated by the non-axisymmetric equilibrium code (e.g., GPEC), the plasma response field is often four orders of magnitude smaller than the axisymmetric equilibrium field. Thus, it is treated as a higher-order correction to the equilibrium magnetic field in the plasma transport equations. Despite its small amplitude, this non-axisymmetric field alters the magnetic topology, forming homoclinic or heteroclinic tangles near the separatrix and directly connecting divertor targets to the core plasma. Consequentially, the divertor heat load exhibits a distinct striation pattern, which was observed in both experiments and our KSTAR simulations. The second model is BSTING, a flux-coordinate independent (FCI) extension of the BOUT++ framework. The versatile FCI method considers plasma as locally field-line aligned when evaluating the parallel derivatives. Simulations of the W7-X stellarator boundary with a pre-mapped magnetic field, including the stochastic layer, will be presented as an example of BSTING applications. These two codes provide alternative modeling tools to study and simulate non-axisymmetric effects in many open topics (e.g., edge instability, turbulence, core-edge integration) at the tokamak and stellarator boundary regions.