Dependence of Peeling-Ballooning Stability on Plasma Shape in the TCV Tokamak : Plasma Shape Effects on TCV Edge Stability

Sammanfattning

Nuclear fusion offers the promise of clean, sustainable and abundant energy to meet the long-term growth in global energy demand. Achieving fusion conditions requires extremely high temperatures on the order of millions of ◦C. The high-confinement mode (H-mode) facilitates these conditions but introduces challenges, particularly through an instability called edge-localised modes (ELMs), which can severely damage internal components of future fusion power plants. ITER, currently under construction in France, aims to demonstrate net energy gain and inform the design of commercial fusion reactors. To support ITER-relevant research, it is essential to reproduce ITER-like operational regimes in existing devices. This thesis investigates whether a peeling- limited ELM stability regime (expected in ITER) can be achieved in the TCV tokamak by modifying the plasma shape. A boundary parametrization was implemented to generate realistic plasma geometries, and the effects of squareness, triangularity and elongation were systematically studied using the Europed and ESSIVE simulation codes. The results show that variations in squareness and triangularity did not facilitate access to a peeling-limited regime; instead, they shifted the stability further from it. In contrast, increasing elongation to approximately κ = 2.0, combined with a higher plasma current of Ip ≈ 230 kA, significantly shifted the stability towards a peeling-limited regime. This effect was most pronounced at low densities (npede = 2.0 · 1019 m−3), which appear favourable, and potentially essential, for achieving the desired peeling-limited stability. These findings provide valuable guidance for future experimental validation in TCV, enabling the study of ITER-like stability regimes. Such investigations may offer insights that contribute to the optimization of ITER’s performance and advancing the prospects of future fusion power generation.