This thesis presents a comprehensive investigation into the observations and suppression of sawtooth instabilities on the High Beta Tokamak-Extended Pulse (HBT-EP) device. The principle and design of a new tangential multi-energy extreme ultraviolet and soft x-ray (ME-EUV/SXR) diagnostic system is presented. This system enables the clear detection of sawtooth events for the first time on HBT-EP. It is the first multi-energy tangential-view system designed to work in a temperature range below 200 eV in a tokamak, which enables measurements of the electron temperature and the examination of mode dynamics. By employing a combination of 0.1 um aluminum and 0.2 um titanium filters, the system allows measurements of electron temperature profiles through reconstruction of the emission profile using the standard ``double-foil'' technique.
Using the tangential ME-EUV/SXR diagnostic system, the thesis reports on the first detailed observations of sawtooth events on HBT-EP, analyzing their features and comparing the findings with results from other devices. It investigates the phenomenon of discharge scenario bifurcation, where plasma exhibits distinct behaviors under similar parameters. The study examines the correlation between the amplitude of the edge mode and the strength of sawtooth events, along with the role of the conducting wall system in this context. It was found that when the normalized wall radius 𝒃/𝒂 is within a critical value, the edge mode can be stabilized and strong sawtooth events occur. In-depth analysis is performed on the modes present during sawtooth-suppressed stages, with a particular focus on the coupling between the 1/1 helical core (HC), 2/1 tearing mode (TM) and the 3/1 external kink mode (𝐗𝐊). Evidence is provided to support the effectiveness of magnetic flux pumping in suppressing sawtooth instabilities when the 3/1 𝐗𝐊 exhibits a significant amplitude. Conversely, the suppression of the 3/1 𝐗𝐊 due to stabilization by the conducting wall leads to the weakening of magnetic flux pumping, resulting in the occurrence of strong sawtooth events.
In conclusion, this thesis contributes to the understanding of sawtooth instabilities on the HBT-EP tokamak and highlights the role of magnetic flux pumping as a mechanism for sawtooth suppression. It broadens the understanding of flux pumping across various tokamak operational regimes and demonstrates the potential of sawtooth suppression through external mode manipulation. This contributes to the future development of sawtooth control strategies, improving plasma stability and advancing fusion energy research.
| Identifer | oai:union.ndltd.org:columbia.edu/oai:academiccommons.columbia.edu:10.7916/snrs-3j72 |
| Date | January 2024 |
| Creators | Li, Boting |
| Source Sets | Columbia University |
| Language | English |
| Detected Language | English |
| Type | Theses |
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