Comparison of local and global gyrokinetic calculations of collisionless zonal flow damping in quasi-symmetric stellarators

Abstract

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Gyrokinetic simulations in stellarators using different computational domains

“…1) for FT, FFS and RG domains for LHD and W7-X configurations are compared in Figure 4. The residual level increases with the radial wavenumber of the perturbation in both LHD and W7-X configurations, in agreement with previous calculations [15,6,19]. However, the residual level for a given radial scale is significantly larger in the case of W7-X as compared with LHD.…”

“…The good agreement between different FTs, of any length, found in LHD for both the linear ITG instability, and for the linear ZF evolution, cannot be considered a situation valid for other devices, in general. The results for the W7-X configuration, as well as previous results in quasisymmetric devices [19], show that the convergence between results from different flux tubes is configuration-dependent. Furthermore, the sampling of the flux surface by flux tubes of increasing lengths is largely conditioned by the rotational transform.…”

“…the comparison of results in different computational domains, because it depends on quantities averaged over the full flux surface and exhibits distinct features in stellarators as compared to tokamaks [17,4,5,18]. This problem has been studied numerically in different stellarator configurations in [14,15,16,27,5,18,28,19] and the low frequency oscillation of ZFs, specific of stellarators, was identified experimentally in TJ-II [30,32]. The relaxation of ZFs has already been studied for the quasisymmetric devices HSX and NCSX in the FT, FFS and RG domains in [19] and in W7-X configurations in FFS and RG computational domains in [6,18].…”

“…This problem has been studied numerically in different stellarator configurations in [14,15,16,27,5,18,28,19] and the low frequency oscillation of ZFs, specific of stellarators, was identified experimentally in TJ-II [30,32]. The relaxation of ZFs has already been studied for the quasisymmetric devices HSX and NCSX in the FT, FFS and RG domains in [19] and in W7-X configurations in FFS and RG computational domains in [6,18]. Here we use the standard configuration of LHD, with R ax = 3.74 m and B 0 = 2.53 T and a high mirror (KJM) configuration of W7-X, with beta 3%.…”

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

“…(2017) and Smoniewski et al. (2021). In non-axisymmetric devices, the relaxation of a zonal potential perturbation typically shows a damped oscillation, reaching a stationary residual level at .…”