München 2019 – scientific programme

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P: Fachverband Plasmaphysik

P 15: Helmholtz Graduate School V - Magnetic Confinement II

P 15.1: Invited Talk

Wednesday, March 20, 2019, 11:00–11:30, HS 21

Turbulence in the Wendelstein 7-X Stellarator — •Adrian von Stechow for the The Wendelstein 7-X Team collaboration — Institut für Plasmaphysik, Greifswald, Germany

A central design goal of magnetic confinement fusion devices is the minimization of heat and particle losses to their walls. The Wendelstein 7-X superconducting stellarator has a neoclassically optimized (and variable) 3D magnetic field geometry, such that turbulent transport can be a major loss channel. These losses are expected from analytical and numerical models to be highly geometry-dependent, both in terms of density and temperature profiles as well as geometrical properties of the field itself, e.g. local flux compression and symmetries such as quasi-isodynamicity. Turbulence in W7-X has therefore been experimentally investigated in the recently completed campaign that demonstrated long pulse operation at high density and triple product using a range of dedicated diagnostics which provide coverage from the plasma core to the scrape-off layer. Comparison of neoclassical transport simulations of plasma profiles with measured ones, as well as radial diffusion coefficient measurements based on particle transport studies suggest that a significant fraction of transport is indeed turbulent. Ion-scale turbulence is generally observed in the confied region, and is shown to be significantly reduced by profile shaping during pellet-fueled discharges while confinement is improved. Gyrokinetic simulations support these findings by showing that ITG and TEM growth rates are minimized when the ion temperature and density gradients are of similar magnitude and spatially overlap.