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Interaction of plasma rotation and resonant magnetic perturbation fields in tokamaks

A. Nicolai, U. Daybelge, M. Lehnen, M. Z. Tokar, B. Unterberg, C. Yarim, JET contributors2008年被引用 5Nuclear FusionIF 3出版社

The interaction between plasma rotation and perturbation fields is described by the ambipolarity constraint and the parallel momentum balance, both emanating from the revisited neoclassical theory, and the electrodynamical screening of the resonant perturbation field at the singular surfaces. This screening depends mainly on the slip between the rotating plasma and the resonant field. The neoclassical theory, valid in the collision dominated regime and accounting for gyro-viscosity, includes arbitrary plasma cross-sections, anomalous viscosity, ponderomotive forces, neutral beam injection (NBI), pressure anisotropization and a momentum source due to ergodicity which has a considerable impact on the plasma rotation as demonstrated in TEXTOR.To estimate the influence of the perturbation coils on the plasma rotation, the radial magnetic field (proportional to the helical flux function) is Fourier analysed (using 'intrinsic' coordinates) and the total field is used for field line tracing thus obtaining the ponderomotive momentum input and the extension Δe of the ergodic layer at the edge. Both procedures account for the full plasma geometry. Δe is assumed to be independent of the rotational state because of the boundary condition Vt = 0. In a second step the obtained velocity profiles are used to compute the screening at the singular layers and thus the reduction of the island width due to plasma rotation.The main results can be summarized as follows.Using in the case of TEXTOR shot #94092 the diffusion coefficient DM = 2 × 10−6 m (typical for the 12/4 configuration) the observed increase in vt by Δvt ≈ 5 km s−1 can be reproduced. Inside the plasma the slip prevents any influence of the ponderomotive forces, thus yielding a constant increase in the vt(r)-profile by Δvt.Assuming in the case of the error field correction coils (n = 1) of JET the current Ihel = 30 kA and using for the plasma background the data of shot #67951 in the static case, an ergodized layer (Δe(n = 1) ≈ 20 cm in the vicinity of the unperturbed x-point) and large m = 2, m = 3 (n = 1) islands (Wm=2,n=1 = 10 cm) are obtained. In the n = 2 configuration the analogous parameters are Δe(n = 2) ≈ 18 cm and Wm = 2,n = 2 = 4 cm i.e. Δe stays roughly the same and the island width is strongly reduced thus indicating the superiority of this configuration. Plasma rotation reduces the width Wm=2,n=1 to a small value. (However, tearing mode physics which may lead to mode locking is not included in this consideration.)

日本語訳

プラズマ回転と摂動場の間の相互作用は、再検討された新古典理論から導出される両極性拘束条件と平行運動量バランス、および特異面における共鳴摂動場の電気力学的遮蔽によって記述される。この遮蔽は主に、回転するプラズマと共鳴場の間のすべりに依存する。衝突支配領域で有効であり、ジャイロ粘性を考慮した新古典理論は、任意のプラズマ断面、異常粘性、ポンデロモーティブ力、中性粒子ビーム入射(NBI)、圧力異方性化、およびTEXTORで実証されたようにプラズマ回転にかなりの影響を与えるエルゴード性による運動量源を含む。摂動コイルがプラズマ回転に及ぼす影響を評価するために、動径磁場(ヘリカル磁束関数に比例)を(「固有」座標を用いて)フーリエ解析し、その全磁場を磁力線追跡に用いることにより、ポンデロモーティブ運動量入力と周辺部におけるエルゴード層の広がりΔeを得る。両手順は完全なプラズマ形状を考慮する。Δeは、境界条件Vt = 0のため、回転状態に依存しないと仮定される。第二段階として、得られた速度分布を用いて特異層における遮蔽を計算し、それによるプラズマ回転に起因する島幅の減少を求める。主な結果は以下のように要約される。TEXTORショット#94092の場合、拡散係数DM = 2 × 10⁻⁶ m(12/4配位に典型的)を用いると、観測されたvtの増加Δvt ≈ 5 km s⁻¹を再現できる。プラズマ内部では、すべりによりポンデロモーティブ力の影響が妨げられ、vt(r)分布の一定の増加Δvtが得られる。JETの誤差場補正コイル(n = 1)の場合、電流Ihel = 30 kAを仮定し、静的場合のショット#67951のデータをプラズマ背景として用いると、エルゴード化層(非摂動x点近傍でΔe(n = 1) ≈ 20 cm)と大きなm = 2、m = 3(n = 1)島(Wm=2,n=1 = 10 cm)が得られる。n = 2配位では、対応するパラメータはΔe(n = 2) ≈ 18 cmおよびWm = 2,n = 2 = 4 cmであり、すなわちΔeはほぼ同じままである一方、島幅は大幅に減少し、この配位の優位性を示している。プラズマ回転はWm=2,n=1を小さな値に減少させる。(ただし、モードロッキングを引き起こす可能性のあるテアリングモード物理はこの考察には含まれていない。)

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jet中精度(概要文一致)textor中精度(概要文一致)

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Magnetic perturbationResonant magnetic perturbationPlasma rotation
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