MHD Database for Design of Quasi-axisymmetric Stellarator

参考CHS实验数据和计算机程序，估算了准轴对称星体CHS-Qa的MHD稳定性。尽管CHS-QA和CHS(低纵横比氦/力矩加速器)的磁构型不同，但两种构型的稳定性标准都应该是可用的。局部互换模式的Mercier判据已被广泛用作评估CHS和LHD磁流体稳定性的指标，因为即使在有限的J3构型中，这两台机器也都具有磁山，这使得构型可能不稳定于理想互换模式。CHS的实验结果表明，有限&lt；β&gt；等离子体并没有表现出对储存能量的任何有害影响，而Mercier判据认为它是不稳定的。最近的CHS实验再次证实了这一结果，真空磁轴比以前更强烈地内移，其中磁山变得更强。最近在LHD实验中也证实了这一点。得出的重要结论是，在评价CHS-QA的MHD稳定性时，不必认真考虑Mercier准则。在有限&lt；β&gt；的CHS-Qa等离子体中，自举电流沿增强真空转动变换的方向流动。电流可能激发撕裂模和外扭结模，其中m=2/n=L模是最危险的。通过在CHS中诱导欧姆电流和束流驱动电流，研究了m=2/n=L的MHD模。同样，这对等离子体性能没有有害影响。由于在CHS的真空中不存在m=2/n=L的共振面，所以实验中不能模拟外扭结模式。利用CHS-QA中的Terpsichore和CAS3D程序对该模式进行了分析。血浆的稳定性高达-lt；β&gt；的2.5-3%。用Terpsichore WBAL和COBRA程序对气球模式进行了分析，给出了高达3%的稳定性&lt；β&gt；。

MHD stability of quasi-axisymmetric stellarator CHS-qa is estimated by referring to CHS experimental data and by using computer codes. Although magnetic configurations of CHS-qa and CHS (low aspect ratio heliotron / torsatron) are different, stability criteria should be available for both configurations. Mercier criterion on the local interchange mode has been widely used as a guideline for evaluating MHD stability of CHS and LHD, because both machines are of a magnetic hill even in the finite J3 configuration, which makes the configurations possibly unstable against ideal interchange modes. Experimental results of CHS showed that finite <β> plasmas, where instabilities are expected from Mercier criterion, did not show any deleterious effect on the stored energy. Recent CHS experiments again confirmed this result for more strongly inward shift of vacuum magnetic axis than before, where the magnetic hill becomes stronger. This was also confirmed recently in LHD experiments. The important conclusion is that it is not necessary to take serious account of Mercier criterion in evaluating MHD stability of CHS-qa. In CHS-qa plasmas with finite <β>, the bootstrap current flows in the direction to augment the vacuum rotational transform. The current might excite tearing modes and external kink modes, where m=2/n=l mode is the most dangerous one. By inducing Ohmic and beam driven currents in CHS, MHD modes with m=2/n=l have been studied. Again there is no deleterious effect on the plasma performance. Because the resonant surface of m=2/n=l can not exist in vacuum in CHS, the external kink mode can not be simulated in the experiment. The mode has been analyzed by using Terpsichore and CAS3D codes in CHS-qa. The plasma is stable up to <β> of 2.5 - 3%. The ballooning mode has been analyzed with Terpsichore WBAL and Cobra codes, giving stability <β> of up to about 3%.