SMuK 2021 – scientific programme
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P: Fachverband Plasmaphysik
P 6: Magnetic Confinement III & Helmholtz Graduate School II
P 6.3: Talk
Tuesday, August 31, 2021, 17:25–17:50, H5
Core plasma density fluctuations in Wendelstein 7-X ECRH plasmas — •Jan-Peter Bähner1, Jorge A. Alcusón1, Søren K. Hansen2, Håkan M. Smith1, Adrian von Stechow1, Zhouji Huang2, Eric M. Edlund3, Miklos Porkolab2, Olaf Grulke1,4, and The W7-X Team1 — 1Max-Planck-Institute for Plasma Physics, Greifswald, Germany — 2MIT Plasma Science and Fusion Center, Cambridge, MA, USA — 3SUNY Cortland, Cortland, NY, USA — 4Technical University of Denmark, Kongens Lyngby, Denmark
Ion-scale turbulence is thought to be the main driver for anomalous transport in the optimised stellarator Wendelstein 7-X (W7-X). The most important instabilities on this scale are the ion-temperature-gradient (ITG) mode and the trapped-electron mode (TEM). The Phase Contrast Imaging (PCI) diagnostic measures line-integrated density fluctuations throughout the plasma core with temporal and wavenumber resolution spanning the ITG and TEM scales. In edge-fuelled, electron cyclotron heated discharges, a localisation of density fluctuations to approximately 75% of the plasma minor radius is shown experimentally via a match of the dominant measured phase velocity of fluctuations to the profile of the E× B rotation velocity and via gyrokinetic simulations with GENE. The localisation and characteristics of the measured fluctuations and gyrokinetic simulations match the expectation of ITG dominated turbulence in W7-X. The dynamic evolution of multiple phase velocities connected to a qualitative change of turbulence during improved confinement after pellet injection as well as low frequency oscillations reminiscent of ZFOs are presented.