Turbulent impurity transport simulations in Wendelstein 7-X plasmas

Abstract

A study of turbulent impurity transport by means of quasilinear and nonlinear gyrokinetic simulations is presented for Wendelstein 7-X (W7-X). The calculations have been carried out with the recently developed gyrokinetic code stella. Different impurity species are considered in the presence of various types of background instabilities: ITG, TEM and ETG modes for the quasilinear part of the work; ITG and TEM for the nonlinear results. While the quasilinear approach allows one to draw qualitative conclusions about the sign or relative importance of the various contributions to the flux, the nonlinear simulations quantitatively determine the size of the turbulent flux and check the extent to which the quasilinear conclusions hold. Although the bulk of the nonlinear simulations are performed at trace impurity concentration, nonlinear simulations are also carried out at realistic effective charge values, in order to know to what degree the conclusions based on the simulations performed for trace impurities can be extrapolated to realistic impurity concentrations. The presented results conclude that the turbulent radial impurity transport in W7-X is mainly dominated by ordinary diffusion, which is close to that measured during the recent W7-X experimental campaigns. It is also confirmed that thermo-diffusion adds a weak inward flux contribution and that, in the absence of impurity temperature and density gradients, ITG- and TEM-driven turbulence push the impurities inwards and outwards, respectively.

arXiv comment19 pages, 10 figures, 2 tables

References in corpus (15)

• Critically balanced ion temperature gradient turbulence in fusion plasmas
• The effect of tangential drifts on neoclassical transport in stellarators close to omnigeneity
• Impurity transport in a mixed-collisionality stellarator plasma
• $\text{stella}$: a mixed implicit-explicit, delta-f gyrokinetic code for general magnetic field configurations
• Collisionless microinstabilities in stellarators II - numerical simulations
• On neoclassical impurity transport in stellarator geometry
• KNOSOS: a fast orbit-averaging neoclassical code for stellarator geometry
• Stellarator impurity flux driven by electric fields tangent to magnetic surfaces
• Electrostatic potential variations on stellarator magnetic surfaces in low collisionality regimes
• Collisional transport of impurities with flux-surface varying density in stellarators
• Large tangential electric fields in plasmas close to temperature screening
• Quasilinear particle transport from gyrokinetic instabilities in general magnetic geometry
• Turbulent transport and heating of trace heavy ions in hot, magnetized plasmas
• The importance of the classical channel in the impurity transport of optimized stellarators
• Effects of collisions on impurity transport driven by electrostatic modes

Cited by in corpus (8)

• An experimental characterization of core turbulence regimes in Wendelstein 7-X
• Prevention of core particle depletion in stellarators by turbulence
• Robust stellarator optimization via flat mirror magnetic fields
• Turbulent transport of impurities in 3D devices
• Electrostatic gyrokinetic simulations in Wendelstein 7-X geometry: benchmark between the codes stella and GENE
• Instabilities and turbulence in stellarators from the perspective of global codes
• Calculating the linear critical gradient for the ion-temperature-gradient mode in magnetically confined plasmas
• Critical gradient optimization for quasi-isodynamic stellarators