Magnetic fluctuations, ambipolarity, charge filamentation, and plasma rotation in tokamaks

Publisher Website
Google Scholar
Abstract
Using the quasilinear kinetic theory of transport, it is shown that, contrary to the conventional description, the particle flow from magnetic fluctuations due to local normal modes is intrinsically ambipolar on spatial average. This follows essentially from the local frame rotational invariance in the direction perpendicular to the magnetic field. The local field perturbations carry no rotational momentum from the plasma, and rotation can be lost only by slow viscous diffusion. While the plasma avoids rapid global charge‐up, local deviations from ambipolarity cause both inward and outward radial electric currents to flow, resulting in charge filamentation of the plasma. The filamentation process can be saturated when balanced against shear viscosity. The charge filaments and corresponding shear in the transverse E×B velocity could be large enough to cause drift‐ and shear‐Alfvén modes to be Kelvin–Helmholtz unstable. These effects are illustrated with numerical solutions of the drift‐Alfvén mode equations. A discussion of tokamak experimental data on plasma potentials and rotational momentum loss, and a theoretical estimate of anomalous ion viscosity are given.