Spatial Structure of Limit-Cycle Oscillations

Bachelor Thesis , 2016 , 129 Pages , Grade: 1,3

Physics - Nuclear Physics

In magnetically confined fusion plasmas it is possible to distinguish between low confinement (L-mode) and high confinement (H-mode). At the transition from L-mode to H-mode and vice versa a phase with intermediate confinement exists, which is also called I-phase. During this intermediate state limit-cycle oscillations (LCO) with a frequency in the low kilohertz range occur, corresponding to fluctuations in the plasma temperature, density and other key parameters.

This work investigates the spatial distribution of these LCOs within the plasma by diode bolometry. The 2D spatial structure of the Iphase as it appears in the diode bolometers is resolved using correlation and coherence techniques between bolometer channels. It is found that limit-cycle oscillations are localized in the region of the magnetic X-point and it is indicated that they are not stationary but poloidal moving along the separatrix during the I-phase.

Inhaltsverzeichnis (Table of Contents)

• Preface
• Abstract
• Nomenclature
• 1 Introduction
• 2 Experimental setup
• 2.1 ASDEX Upgrade
• 2.1.1 Setup
• 2.1.2 Magnetic field
• 2.1.3 Divertors
• 2.2 Diagnostics
• 2.2.1 Mirnov coils
• 2.2.2.1 Functionality
• 2.2.2 Bolometry
• 2.2.2.2 Setup and spatial resolution
• 3 Theoretical background
• 3.1 Plasma confinement
• 3.1.1 Energy confinement time and Lawson criterion
• 3.1.2 L-mode
• 3.1.3 H-mode
• 3.1.4 I-phase and limit-cycle oscillations.
• 3.2 Data analysis
• 3.2.1 Fourier-based analysis
• 3.2.1.1 Fast Fourier transform
• 3.2.1.2 Power Spectral Density
• 3.2.1.3 Spectrogram
• 3.2.1.4 Example

• College: Technical University of Munich (Max-Planck-Institut für Plasmaphysik)
• Grade: 1,3
• Author: Bernd Kohler (Author)
• Publication Year: 2016
• Pages: 129
• Catalog Number: V342545
• ISBN (eBook): 9783668330504
• ISBN (Book): 9783668330511
• Language: English
• Tags: Plasmaphysik, Kernfusion, Fusion, ITER, ASDEX, ASDEX Upgrade, IPP, Max-Planck-Institut, Fusionsplasma, I-phase, Limit-cycle oscillation, Bolometer, Korrelation, Kohärenz, Räumliche Struktur, Lawson Kriterium, Deuterium, Tritium, Spektrogramm, Abtastfrequenz, Nyquist-Shannon Theorem, Plasmaheizung, DEMO, Fourier Analysis, L-mode, H-mode, Photodiode, Bachelorarbeit, TUM, Technische Universität München, Ulrich Stroth