Abstract
The GENE-3D code, the global stellarator version of the established GENE framework, has been extended to an electromagnetic gyrokinetic code. This paper outlines the basic structure of the algorithm, highlighting the treatment of the electromagnetic terms. The numerical implementation is verified against the radially global GENE code in linear and nonlinear tokamak simulations, recovering excellent agreement between both codes. As a first application to stellarator plasmas, linear and nonlinear global simulations with kinetic electrons of ion temperature gradient (ITG) turbulence in Wendelstein 7-X were performed, showing a decrease of ITG activity through the introduction of electromagnetic effects via a finite plasma- $\beta$ . The upgrade makes it possible to study a large variety of new physical scenarios, including kinetic electron and electromagnetic effects, reducing the gap between gyrokinetic models and physically realistic systems.
Highlights
Wendelstein 7-X (W7-X) is the first stellarator that has been optimised for low neoclassical transport (Wolf 2008), besides other criteria
For values of β between 1.4 % and 1.75 % one can observe a transition of dominant modes from an ion temperature gradient (ITG) mode to a kinetic ballooning mode (KBM), which can be identified by the rapid increase in the mode frequency
Both linear and nonlinear simulations show a consistent reduction of ITG activity through electromagnetic effects for the given plasma-β
Summary
Wendelstein 7-X (W7-X) is the first stellarator that has been optimised for low neoclassical transport (Wolf 2008), besides other criteria. As such, it has been shown (Klinger et al 2019) that turbulence has become the limiting factor in the confinement for a broad range of its experiments. Using some of the world’s most powerful supercomputers, it is possible nowadays to simulate gyrokinetic turbulence in stellarators globally, making it possible to take into account the full variation of the magnetic field on a flux surface while simultaneously considering its radial variations as well as temperature and density profiles – all of which are inherently impossible in flux-tube simulations.
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