Abstract
In the wall-stabilized high-β plasmas in JT-60U and DIII-D, interactions between energetic particle (EP) driven modes (EPdMs) and edge localized modes (ELMs) have been observed. The interaction between the EPdM and ELM are reproducibly observed. Many EP diagnostics indicate a strong correlation between the distorted waveform of the EPdM and the EP transport to the edge. The waveform distortion is composed of higher harmonics (n ⩾ 2) and looks like a density snake near the plasma edge. According to statistical analyses, ELM triggering by the EPdMs requires a finite level of waveform distortion and pedestal recovery. ELM pacing by the EPdMs occurs when the repetition frequency of the EPdMs is higher than the natural ELM frequency. EPs transported by EPdMs are thought to contribute to change the edge stability.
Highlights
For a fusion reactor, high-β operation is advantageous to achieve higher fusion output power, because the fusion output is proportional to the square of β [1]
We have observed that the edge localized modes (ELMs) can be triggered by the EPdriven modes in JT-60U and DIII-D
Many energetic particle (EP) diagnostics indicate a strong correlation between the distorted waveform of the energetic-particle-driven modes (EPdMs) required to trigger an ELM and the EP transport to edge
Summary
High-β operation is advantageous to achieve higher fusion output power, because the fusion output is proportional to the square of β [1]. The high-β regime between the no-wall and ideal-wall MHD limits is achievable with a conducting wall close to the plasma to stabilize ideal kink-ballooning modes that limit the β-value [2]. This regime can be called the ‘wall-stabilized high-β regime’. ELM triggering by the EPdM has been observed on DIII-D These observations in both devices imply a new common MHD physics in high-β plasmas suggesting that the EP contribution is important even for edge stability in high-β burning plasmas.
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