Mainz 2022 – scientific programme
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P: Fachverband Plasmaphysik
P 19: Poster II
P 19.7: Poster
Thursday, March 31, 2022, 16:00–17:30, P
Investigation of spontaneous transitions to high core-electron temperatures in W7-X low-iota plasmas — •Juan Fernando Guerrero Arnaiz1,2, Andreas Dinklage1,2, Axel Könies2, Carolin Nührenberg2, Bernd Pompe1, Alessandro Zocco2, Matthias Hirsch2, Udo Höfel2, Christian Brandt2, Joachim Geiger2, Kian Rahbarnia2, Jonathan Schilling2, John Schmitt3, Henning Thomsen2, and the W7-X Team2 — 1Universität Greifswald, Greifswald Germany — 2Max-Planck-Institut für Plasmaphysik, Greifswald Germany — 3Auburn University
Spontaneous transitions to higher core-electron temperatures preserving the electron pressure were detected in the so-called low-iota configuration of W7-X. Data mining employing a large data set at different heating powers and densities was conducted. Permutation Entropy as a fast and robust novelty detection method was used to characterize the conditions for the occurrence of a core-localized spatio-temporal bifurcation. To investigate the transition mechanism in more detail, highly sampled electron cyclotron emission and soft-X ray data reveal low-coherent fluctuations which disappeared when higher electron temperatures were attained. First analysis of the effects due to the evolving bootstrap current indicates a change of the rotational transform (iota) profile temporarily crossing low-order rational values. The same neoclassical analysis indicates that a transition into the stellarator-specific core electron-root confinement regime would be consistent with the observed increase of the central electron temperature. The role of rational iota values is being assessed in MHD stability studies.