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Resistive wall mode stabilization in slowly rotating high beta plasmas

机译：缓慢旋转的高β等离子体中的电阻壁模式稳定

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DIII-D experiments show that the resistive wall mode (RWM) can remain stable in high beta scenarios despite a low net torque from nearly balanced neutral beam injection heating. The minimization of magnetic field asymmetries is essential for operation at the resulting low plasma rotation of less than 20 krad s(-1) (measured with charge exchange recombination spectroscopy using C vi emission) corresponding to less than 1% of the Alfven velocity or less than 10% of the ion thermal velocity. In the presence of n=1 field asymmetries the rotation required for stability is significantly higher and depends on the torque input and momentum confinement, which suggests that a loss of torque-balance can lead to an effective rotation threshold above the linear RWM stability threshold. Without an externally applied field the measured rotation can be too low to neglect the diamagnetic rotation. A comparison of the instability onset in plasmas rotating with and against the direction of the plasma current indicates the importance of the toroidal flow driven by the radial electric field in the stabilization process. Observed rotation thresholds are compared with predictions for the semi-kinetic damping model, which generally underestimates the rotation required for stability. A more detailed modeling of kinetic damping including diamagnetic and precession drift frequencies can lead to stability without plasma rotation. However, even with corrected error fields and fast plasma rotation, plasma generated perturbations, such as edge localized modes, can nonlinearly destabilize the RWM. In these cases feedback control can increase the damping of the magnetic perturbation and is effective in extending the duration of high beta discharges.
机译：DIII-D实验表明，尽管由于接近平衡的中性束注入加热而产生的净转矩较低，但电阻壁模式（RWM）在高beta情况下仍可保持稳定。磁场不对称性的最小化对于在小于20 krad s（-1）的低等离子旋转（通过使用C vi发射的电荷交换复合光谱法测量）下产生的低等离子旋转（小于Alfven速度的1％或以下）进行操作时至关重要超过离子热速度的10％在存在n = 1个磁场不对称的情况下，稳定性所需的旋转明显更高，并且取决于扭矩输入和动量限制，这表明扭矩平衡的损失会导致有效旋转阈值超过线性RWM稳定性阈值。在没有外部施加磁场的情况下，测得的旋转可能太低而无法忽略反磁性旋转。在以等离子体电流的方向旋转和逆着等离子体电流的方向旋转的等离子体中，不稳定开始的比较表明，在稳定过程中，由径向电场驱动的环形流动的重要性。将观察到的旋转阈值与半动力学阻尼模型的预测进行比较，该模型通常会低估稳定性所需的旋转。包括抗磁和进动漂移频率在内的动力学阻尼的更详细建模可以在没有等离子体旋转的情况下实现稳定性。但是，即使具有校正的误差场和快速的等离子体旋转，等离子体产生的扰动（例如边缘局部模式）也可能使RWM非线性不稳定。在这些情况下，反馈控制可以增加磁扰动的阻尼，并有效地延长高β放电的持续时间。

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