Global gyrokinetic particle simulations of microturbulence in W7-X and LHD stellarators

Abstract

Global gyrokinetic particle simulations of electrostatic ion temperature gradient (ITG) instability show that the most unstable eigenmode is localized to some magnetic fieldlines or discrete locations on the poloidal plane in the Wendelstein 7-X (W7-X) stellarator due to its mirror-like magnetic fields, which vary strongly in the toroidal direction and induce coupling of more toroidal harmonics (n) to form the linear eigenmode than in the Large Helical Device (LHD) stellarator. Nonlinear electrostatic simulation results show that self-generated zonal flows are the dominant saturation mechanism for the ITG instabilities in both the LHD and W7-X. Furthermore, radial widths of the fluctuation intensity in both the LHD and W7-X are significantly broadened from the linear phase to the nonlinear phase due to turbulence spreading. Finally, nonlinear spectra in the W7-X are dominated by low-n harmonics, which can be generated both by nonlinear toroidal coupling of high-n harmonics and by linear toroidal coupling with large amplitude zonal flows due to the 3D equilibrium magnetic fields.

Global electromagnetic turbulence simulations of W7-X-like plasmas with GENE-3D

“…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. As such, studies like those of Navarro et al (2020), Cole et al (2020), Sánchez et al (2020) and Wang et al (2020) have paved the way in investigating ion temperature gradient (ITG) turbulence globally in stellarators.…”

Self-consistent, global, neoclassical radial-electric-field calculations of electron-ion-root transitions in the W7-X stellarator

“…An earlier attempt to simulate the electron-ion-root transition self-consistently was undertaken in [14] using the code GTC [15], wherein buffer zones were introduced in the field equation. Although the simulations are global within the scope of their computational domain, the presence of these buffer zones at the boundaries could potentially influence the solution.…”

Electrostatic gyrokinetic simulations in Wendelstein 7-X geometry: benchmark between the codes stella and GENE

“…2020; Wang et al. 2020). In the context of verification between stellarator gyrokinetic codes, comparisons have also been reported.…”

“…While existing tokamak gyrokinetic codes (Parker, Lee & Santoro 1993;Kotschenreuther, Rewoldt & Tang 1995;Lin 1998;Dorland et al 2000;Jenko 2000;Candy & Waltz 2003;Jolliet et al 2007;Peeters et al 2009) have been extensively exploited and tested, less work has been carried out in the validation and verification of stellarator gyrokinetic codes (Kornilov et al 2004;Baumgaertel et al 2011;Barnes, Parra & Landreman 2019;Cole et al 2019;Maurer et al 2020;Wang et al 2020). In the context of verification between stellarator gyrokinetic codes, comparisons have also been reported.…”