Effects of the radial electric field in a quasisymmetric stellarator

Abstract

Recent calculations have shown that a radial electric field can significantly alter the neoclassical ion heat flux, ion flow, bootstrap current and residual zonal flow in a tokamak, even when the E × B drift is much smaller than the ion thermal speed. Here we show the novel analytical methods used in these calculations can be adapted to a quasisymmetric stellarator. The methods are based on using the conserved helical momentum ψ* instead of the poloidal or toroidal flux as a radial coordinate in the kinetic equation. The banana-regime calculations also employ a model collision operator that keeps only the velocity-space derivatives normal to the trapped-passing boundary, even as this boundary is shifted and deformed by the E × B drift. We prove the isomorphism between quasisymmetric stellarators and tokamaks extends to the finite-E × B generalizations of both banana-regime and plateau-regime neoclassical theory and the residual zonal flow. The plateau-regime results may be relevant to the HSX stellarator, and both the plateau- and banana-regime results can be used to validate stellarator transport codes.