From information flow to transport investigations in fusion: revealing the nature of transitions to core-electron-root-confinement in Wendelstein 7-X

Medientyp: E-Book; Hochschulschrift

Titel: From information flow to transport investigations in fusion : revealing the nature of transitions to core-electron-root-confinement in Wendelstein 7-X

Beteiligte: Guerrero Arnaiz, Juan Fernando [Verfasser:in]; Dinklage, Andreas [Akademische:r Betreuer:in]; Albert, Christopher [Akademische:r Betreuer:in]; Suzuki, Yasuhiro [Akademische:r Betreuer:in]

Körperschaft: Universität Greifswald

Erschienen: Greifswald, 31.07.2023

Umfang: 1 Online-Ressource (PDF-Datei: 108 Seiten, 22444 Kilobyte); Illustrationen (farbig), Diagramme (farbig)

Sprache: Englisch

Identifikator:

RVK-Notation: UR 9000 : Kontrollierte Kernfusion

Schlagwörter: Wendelstein 7-X > Fusion > Stellarator > Informationstheorie > Entropie

Entstehung:

Hochschulschrift: Dissertation, Mathematisch-Naturwissenschaftliche Fakultät der Universität Greifswald, 2023

Anmerkungen: Literaturverzeichnis: Seite 30-36. - Literaturangaben

Beschreibung: Magnetic Confinement, Wendelstein 7-X

In course of the recent results from Wendelstein 7-X, stellarators are on the brink for assessing their maturity as a fusion reactor. To this end, stellarator speciﬁc transport regimes need detailed exploration both with appropriate systematic experimental investigations and models. A way to enhance the efﬁciency of this process is seen in an systematic evaluation of existing experimental data. We propose appropriate tools developed in information theory for examining large datasets. Information entropy calculations, that have proven to assist the systematic assessment of datasets in many other scientiﬁc ﬁelds, are used for novelty detection. Potentially, as a ﬁrst use-case of this holistic process, this thesis attempts to link and to develop approaches to examine the stellarator speciﬁc core-electron-root-conﬁnement (CERC) regime. The speciﬁc interest for CERC emerges from the behavior of the radial electric ﬁeld. While ion-root conditions exhibit negative radial electric ﬁelds, CERC’s positive ﬁeld in the very core of fusion grade plasmas adds an outward thermodynamic force to high-Z impurities and could add to potential actuators to control impurity inﬂux as to be examined for full-metal wall operation in large stellarators. Recently, this feature received revived intent for reactor scale stellarators. Also, in this work, parameter regions close to the transition from ion-root to CERC are examined. At lower rotational transform (a characteristic feature of the magnetic ﬁeld conﬁning fusion grade plasmas), transitions were detected when the plasma current evolved. As in smaller stellarators, it is concluded that low-order rationals and magnetic islands are related to the transitions. This is widely supported by extensive MHD simulations which ﬁnally provide indications for the role of zonal ﬂow oscillations. As one of the outcomes, gyrokinetic instabilities are seen interacting for the ﬁrst time with the neoclassical mechanisms in experiments. In order to cope with the vast number of highly sampled spatio-temporal plasma data, new techniques for novelty detection are required. Fundamental prerequisites for the detailed physics investigations were the feasibility study of entropy-based data analysis techniques, and their adaptation to detect previously unrevealed transition mechanisms. These tools were applied to multivariate bulk plasma emissivity data, which allowed the exploration of large parameter spaces and provided insights in the spatio-temporal dynamics of CERC transitions. In this manner, this research highlights the feasibility of information ﬂow measure analysis in fusion studies. Applications of different entropy-based complexity measures are explored and this work sheds light on the capabilities, added value and limitations of these techniques. This investigation presents the integration of information ﬂow measures to gain deeper understanding of plasma transport phenomena, by providing an approach to fast systematic data mining suited for real-time analysis. This work paves the way for further development and implementation of information-theoretic methods for plasma data analysis. In summary, this research highlights the gained insight on CERC transitions, while showcasing the feasibility, added values and limitations of information ﬂow measure analysis for fusion studies, to induce theory based analysis revealing new insights in fundamental, stellarator-speciﬁc transport mechanisms.

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