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Confinement improvement during detached phase with RMP application in deuterium plasmas of LHD

M. Kobayashi, R. Seki, Y. Hayashi, T. Oishi, K. Tanaka, Y. Takemura, K. Ida, T. Kinoshita, K. Mukai, S. Morita2022年被引用 3Nuclear FusionIF 3出版社

In order to explore the compatibility of good core plasma performance with divertor heat load mitigation, the interaction between cold edge plasma and core plasma transport, including the edge transport barrier (ETB), has been analysed in the divertor detachment discharges of deuterium plasmas in LHD with resonant magnetic perturbation (RMP) field application. The RMP application introduces a widened edge stochastic layer and sharp boundary in the magnetic field structure between the confinement region and the edge stochastic layer. The widened edge stochastic layer enhances impurity radiation and provides stable detachment operation as compared with the case without RMP. It is found that ETB is formed at the confinement boundary at the onset of detachment transition. However, as the detachment deepens, the resistive pressure gradient-driven MHD mode is excited, which degrades the ETB. At the same time, however, the core transport decreases to keep global plasma stored energy (Wp) unchanged, showing clear core-edge coupling. After a gradual increase of density fluctuation during the MHD activity, a spontaneous increase of Wp and the recovery of ETB are observed while the detachment is maintained. Then, the coherent MHD mode ceases and ELM-like bursts appear. In the improved mode, impurity decontamination occurs, and the divertor heat load increases slightly. Key controlling physical processes in the interplay between core and cold edge plasma are discussed. A comparison between deuterium and hydrogen plasmas shows that hydrogen plasmas exhibit similar features to the deuterium ones in terms of density and magnetic fluctuations, impurity decontamination towards higher confinement, etc. But most of the features are modest in the hydrogen plasmas and thus no clear confinement mode transition with clear ETB formation is defined. Better global confinement is obtained in the deuterium plasmas than the hydrogen ones at a higher radiation level.

日本語訳

良好なコアプラズマ性能とダイバータ熱負荷低減の両立可能性を探求するため、LHDにおける共鳴磁場摂動(RMP)印加下のダイバータ非接触状態の重水素プラズマにおいて、周辺輸送障壁(ETB)を含む冷たい周辺プラズマとコアプラズマ輸送の相互作用を解析した。RMP印加は、閉じ込め領域と周辺領域の間の磁場構造における鋭い境界とともに、拡大された周辺ストカスティック層を導入する。拡大されたストカスティック層は不純物放射を増強し、RMP非印加の場合と比較して安定した非接触運転を実現する。非接触状態への遷移開始時に閉じ込め境界でETBが形成されることが見出された。しかしながら、非接触状態が深化するにつれて、抵抗性圧力勾配駆動MHDモードが励起され、ETBを劣化させる。同時に、コア輸送は減少して全プラズマ蓄積エネルギー(Wp)を維持し、コア・周辺結合の明確な証拠を示す。MHD活動中の密度変動が徐々に増加した後、非接触状態を維持したままWpの自発的な増加とETBの回復が観測される。その後、コヒーレントなMHDモードは消滅し、ELM様バーストが出現する。改善モードにおいては、不純物除去が達成される一方、ダイバータ熱負荷はわずかに増加する。コアと冷たい周辺プラズマの相互作用における鍵となる物理過程について議論する。重水素プラズマと水素プラズマの比較から、水素プラズマは密度・磁場変動、高閉じ込め状態への不純物除去などの点で重水素プラズマと類似した特徴を示すが、その大部分は穏やかであり、明確なETBを伴う明確な閉じ込めモード遷移は定義されない。より高い放射レベルにおいて、重水素プラズマは水素プラズマよりも優れた全体閉じ込めを達成する。

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lhd高精度(タイトル一致)

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DeuteriumResonant magnetic perturbationLHDDeuterium plasma
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