The transition from small edge-localized modes (ELMs) to large ELMs has been repetitively observed in minute-scale long-pulse high-confinement mode (H-mode) discharges during the 2017 EAST campaign. The appearance of large ELMs is found to be strongly correlated with the decrease in separatrix density due to the gradual decrease in fuel recycling during long-pulse H-mode operations (LPHOs). By the numerical scanning of separatrix density with a fixed temperature profile, it has been found that the dependence of ELM instability on separatrix density is related to the competition between the ion diamagnetic stabilizing effect and destabilizing effect of pressure gradient and current density in the pedestal region. This sheds light on a comprehensive understanding of the different roles of separatrix density in ELM instability observed during EAST experiments. With a high separatrix density, the ideal ballooning mode can be destabilized near the separatrix, which is thought to help achieve small ELMs in EAST LPHOs. During the 2021 EAST campaign, an experiment of large ELM control was performed through actively changing fuel recycling by moving the strike point location on the lower tungsten divertor target plate. It has been demonstrated that the mitigation of large ELMs is strongly correlated with the significant increase in separatrix density, which is thought to be attributed to a higher ionization source in the scrape-off layer (SOL) region by SOLPS-ITER simulation. The high ionization source in the SOL region is believed to provide a strong fueling effect near the separatrix and thus raise the local density, which is considered an important reason for triggering ballooning instabilities near the separatrix and achieving small ELMs.
小規模な周辺局在モード(ELM)から大規模ELMへの遷移は、2017年のEASTキャンペーン期間中に、分スケールの長時間パルス高閉じ込めモード(Hモード)放電において繰り返し観測された。大規模ELMの出現は、長時間パルスHモード運転(LPHO)中に燃料リサイクリングが漸減することによるセパラトリクス密度の低下と強く相関していることが見出された。温度分布を固定したセパラトリクス密度の数値スキャンにより、ELM不安定性のセパラトリクス密度依存性が、ペデスタル領域におけるイオン反磁性安定化効果と、圧力勾配および電流密度の不安定化効果との間の競合に関連することが見出された。これは、EAST実験で観測されたELM不安定性におけるセパラトリクス密度の異なる役割の包括的理解に光を当てるものである。高いセパラトリクス密度