Generation and damping of neoclassical plasma flows in stellarators

Abstract

A moments method approach for stellarator transport is developed and applied to devices embodying the three forms (quasihelical, quasitoroidal, and quasipoloidal) of stellarator quasisymmetry. Plasma parameter regimes are considered that lead both to stable electron and ion ambipolar electric field roots. The predicted flux surface averaged plasma flow velocity components and their two-dimensional variation within a flux surface are calculated and they approximately reflect the underlying symmetries in the magnetic field structure. Comparison of the shearing rates of the flows with linear stability growth rates for the ion temperature gradient mode indicates that shearing rates (driven by ambipolar transport) can be comparable to growth rates even in the absence of external flow drive.