The effect of a subsonic flow, inherent to most stellarators because of a radial electric field, on their ideal magnetohydrodynamic (MHD) stability properties is studied employing the quasi-Lagrangian picture developed by Frieman and Rotenberg (1960 Rev. Mod. Phys.32 898). The Mach number of the perpendicular E × B flow in stellarators is of order 0.01 and, therefore, admits the usage of a subsonic approximation in form of a static equilibrium. A mathematical formulation of the weak form of the stability equation with flow has been implemented in the ideal-MHD stability code CAS3D. This formulation uses magnetic coordinates and does not involve any derivatives across magnetic surfaces. In addition to the expected Doppler shift of frequencies, properties of the spectrum of the ideal MHD force operator, which are already known for tokamaks, but now also shown in the stellarator case, are: firstly, the appearance of unstable flow-induced continua stemming from the coupling of sound and Alfvén continuum branches with equal mode numbers; and, secondly, the existence of flow-induced, global, stable modes near extrema of sound continuum branches, the extrema, in turn, being generated by the influence of a sheared flow on the static sound continua.
恒星器固有的由于径向电场引起的亚声速流动对其理想磁流体动力学（MHD）稳定性的影响，采用由Frieman和Rotenberg（1960 Rev. Mod. Phys. 32 898）发展的准拉格朗日图像进行研究。恒星器中垂直E×B流动的马赫数约为0.01量级，因此允许采用静态平衡形式的亚声速近似。含流动的稳定性方程的弱形式数学表述已在理想MHD稳定性代码CAS3D中实现。该表述使用磁坐标，且不涉及跨磁面的导数。除了预期的频率多普勒频移外，理想MHD力算子的谱性质（在托卡马克中已知，现也在恒星器情形中展示）包括：第一，由于声连续谱与阿尔芬连续谱分支在相同模数下的耦合，出现不稳定的流动诱导连续谱；第二，存在流动诱导的全局稳定模，这些模位于声连续谱极值附近，而该极值本身是由剪切流动对静态声连续谱的影响所产生的。