DIII-D experiments demonstrate that high pressure, broad current profile equilibria can be accessed in the high poloidal beta regime by optimizing the MHD mode control poloidal spectrum. A novel, variable spectrum (VS) magnetic feedback scheme implemented using the DIII-D internal non-axisymmetric coils (I-coils) facilitated access to reduced internal inductance operation above the no-wall beta limit compared with both no feedback and fixed spectrum feedback. In addition, the VS feedback helped avoid beta collapses caused by marginally unstable resistive wall mode activity. The lower and upper I-coil rows were configured in two independent feedback loops, allowing the feedback field's poloidal spectrum to vary and track changes in the plasma mode structure as the edge safety factor q95 varied from 11 to 6 during the discharges. The q95 dependence of the measured phase difference between the lower and upper I-coil rows during VS feedback is qualitatively compatible with ideal MHD simulations of the least-stable plasma kink mode and with plasma response simulations that included kinetic modifications to ideal MHD. The VS feedback approach is a straightforward way to improve resilience to variations in mode structure that occur as plasma parameters change. The demonstrated expansion of the operating space to lower is expected to improve the coupling of the plasma kink mode to external fields and beneficial wall eddy currents, and is compatible with high bootstrap fraction operation.
この論文では、DIII-Dの実験で、I-コイルを使った可変スペクトル(VS)磁気フィードバックにより、内部インダクタンスの低い高圧プラズマが得られ、壁安定化限界を超えられることが示された。VSフィードバックにより、抵抗壁モードの不安定性を回避でき、プラズマパラメータの変化に対するモード構造の変化にも対応できる。この手法は、高ブートストラップ割合の運転に適し、プラズマキンクモードと外部磁場やエッジ渦電流との結合を改善できる。