Abstract
We present initial results in the development of a gyrokinetic particle-in-cell code for the whole-volume modeling of stellarators. This is achieved through two modifications to the X-point Gyrokinetic Code (XGC), originally developed for tokamaks. One is an extension to three-dimensional geometries with an interface to Variational Moments Equilibrium Code (VMEC) data. The other is a connection between core and edge regions that have quite different field-line structures. The VMEC equilibrium is smoothly extended to the edge region by using a virtual casing method. Non-axisymmetric triangular meshes in which triangle nodes follow magnetic field lines in the toroidal direction are generated for field calculation using a finite-element method in the entire region of the extended VMEC equilibrium. These schemes are validated by basic benchmark tests relevant to each part of the calculation cycle, that is, particle push, particle-mesh interpolation, and field solver in a magnetic field equilibrium of Large Helical Device including the edge region. The developed code also demonstrates collisionless damping of geodesic acoustic modes and steady states with residual zonal flow in the core region.
Highlights
Gyrokinetic simulation is a powerful tool to explore kinetic plasma dynamics with a scale comparable to magnetic fusion devices, and it is widely used to investigate anomalous and neoclassical transport phenomena in the core region, where centrally heated plasmas and energetic particles are primarily confined
We extend the Variational Moments Equilibrium Code (VMEC) equilibrium defined for the core region by using a virtual casing method to include the stellarator edge region in the simulation
A gyrokinetic particle-in-cell simulation code for whole-volume modeling of stellarators has been developed by extending X-point Gyrokinetic Code (XGC), which was originally developed for tokamaks
Summary
Gyrokinetic simulation is a powerful tool to explore kinetic plasma dynamics with a scale comparable to magnetic fusion devices, and it is widely used to investigate anomalous and neoclassical transport phenomena in the core region, where centrally heated plasmas and energetic particles are primarily confined. Phenomenological fluid models are mainly employed for the edge region where the hot plasma makes contact with material walls along open magnetic field lines. Total-f scheme is employed in XGC to address this difficulty This scheme combines the fine-grained delta-f particle-in-cell scheme with a Eulerian description of background plasma dynamics in coarse-grained five-dimensional phase space [7,8,9]. The field-aligned mesh can minimize numerical diffusion in particle-mesh interpolation and enables accurate interpolation of mode structures that vary slowly along magnetic field lines. Another complexity is the stochastic magnetic field structures in the edge region. The “scatter” and “gather” processes are particle-mesh interpolation to evaluate the charge density on the mesh from the marker particles and the electrostatic force acting on a marker particle, respectively
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