Electrostatic microturbulence in W7-X: comparison of local gyrokinetic simulations with Doppler reflectometry measurements
Nuclear Fusion(2023)
Abstract
The first experimental campaigns of Wendelstein 7-X (W7-X) have shown that
turbulence plays a decisive role in the performance of neoclassically optimized
stellarators. This stresses the importance of understanding microturbulence
from the theoretical and experimental points of view. To this end, this paper
addresses a comprehensive characterization of the turbulent fluctuations by
means of nonlinear gyrokinetic simulations performed with the code stella in
two W7-X scenarios. In the first part of the paper, the amplitude of the
density fluctuations is calculated and compared with measurements obtained by
Doppler reflectometry (DR) in the OP1 experimental campaigns. It is found that
the trend of the fluctuations along the radius is explained by the access of
the DR system to different regions of the turbulence wavenumber spectrum. In
the second part of the article, frequency spectra of the density fluctuations
and the zonal component of the turbulent flow are numerically characterized for
comparisons against future experimental analyses. Both quantities feature broad
frequency spectra with dominant frequencies of O(1)-O(10) kHz.
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