Equilibrium Flow Structure with Multiple Ion Species in Magnetically Confined Plasmas of an Arbitrary Aspect Ratio

Abstract

Equilibrium flows of impure plasmas in magnetically confined plasmas of arbitrary aspect ratio are calculated by neoclassical theory. For magnetically confined plasmas with the inverse aspect ratio approaching unity from below, the variation of the magnetic field strength along the field becomes large and as a consequence strong Mirror force arises to trap particles in the magnetic mirror. Thus we expect poloidal flows are weak and we show that this is indeed true for ion and impurity flows by using the Moment approach in banana regime. In contrast, it is shown that appreciable amount of flows exist in collisional regime. Collisional impurities in the spherical tokamak edge are used as a prototypical example of such a case. The flow exhibits strong poloidal variation. As a consequence, strong effective parallel flow shear accumulates in the high field side. Implications on controlling fluctuations and meso-scale structures are discussed.