Stabilization of the vertical instability by non-axisymmetric coils
Stabilization of the vertical instability by non-axisymmetric coils
复制标题
通过非轴对称线圈稳定垂直不稳定性
DOI：
10.1088/0029-5515/56/8/086006
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
R. Buttery
中科院分区：
文献类型：
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作者：
A. Turnbull;A. Reiman;L. Lao;W. Cooper;N. Ferraro;R. Buttery
在发表的《物理评论快报》（Reiman 2007 Phys. Rev. Lett. 99 135007）中，表明可以通过在等离子体上方和下方放置一组与恒定环形平面成一定角度的平行四边形线圈来提高轴对称（或垂直）稳定性。这种稳定的物理原理可以理解为提供有效的附加正稳定性指数。最初的工作基于直托卡马克的简化模型，并不直接适用于有限纵横比、强形状等离子体，例如 DIII-D。在真实的类似 DIII-D 的配置中进行数值计算，以提供 3-D 场实际上可以提高预测的伸长极限的原理证明。采用环形几何结构开发了四场周期梯形线圈组，并使用 10kA、100kA 和 500kA 的梯形线圈电流计算 3D 平衡。对于 n = 0 对称性保持族，理想的磁流体动力学增长率被计算为保形壁位置的函数。结果表明，对于两个较低线圈电流的情况，稳定壁位置的相对改善并不显着，大约为 10−3 或更小。相比之下，当线圈电流增加到 500 kA 时，边缘壁位置增加了 7%，证实了原始研究在实际几何情况下的主要预测。在 DIII-D 中，边缘墙位置移动 7% 相当于能够将现有墙向外移动 5 至 10 厘米。虽然预测对轴对称稳定性的影响是真实的，但它似乎需要比现有设施升级所能提供的更高的线圈电流。对线圈节距、场周期数和线圈位置以及等离子体参数（例如内部电感 ℓi、β 和 q95）进行额外优化将缓解这一问题，但似乎不太可能改变结论。
In a published Physical Review Letter (Reiman 2007 Phys. Rev. Lett. 99 135007), it was shown that axisymmetric (or vertical) stability can be improved by placing a set of parallelogram coils above and below the plasma oriented at an angle to the constant toroidal planes. The physics of this stabilization can be understood as providing an effective additional positive stability index. The original work was based on a simplified model of a straight tokamak and is not straightforwardly applicable to a finite aspect ratio, strongly shaped plasma such as in DIII-D. Numerical calculations were performed in a real DIII-D -like configuration to provide a proof of principal that 3-D fields can, in fact raise the elongation limits as predicted. A four field period trapezioid-shaped coil set was developed in toroidal geometry and 3D equilibria were computed using trapezium coil currents of 10 kA, 100 kA, and 500 kA. The ideal magnetohydrodynamics growth rates were computed as a function of the conformal wall position for the n = 0 symmetry-preserving family. The results show an insignificant relative improvement in the stabilizing wall location for the two lower coil current cases, of the order of 10−3 and less. In contrast, the marginal wall position is increased by 7% as the coil current is increased to 500 kA, confirming the main prediction from the original study in a real geometry case. In DIII-D the shift in marginal wall position of 7% would correspond to being able to move the existing wall outward by 5 to 10 cm. While the predicted effect on the axisymmetric stability is real, it appears to require higher coil currents than could be provided in an upgrade to existing facilities. Additional optimization over the pitch of the coils, the number of field periods and the coil positions, as well as plasma parameters, such as the internal inductivity ℓi, β, and q95 would mitigate this but seem unlikely to change the conclusion.