Nonlinear neoclassical transport in a rotating impure plasma with large gradients

Abstract

The theory of neoclassical transport in an impure toroidal plasma is extended to allow for larger pressure and temperature gradients and faster toroidal rotation than are usually considered. Under these conditions, the density of heavy impurities is not constant on flux surfaces, and the neoclassical transport becomes a nonlinear function of the gradients. Rapid toroidal rotation increases the transport, which can significantly exceed the conventional Pfirsch–Schlüter value if the impurity Mach number is of order unity. In a plasma with steep density or temperature profile, the transport is severely reduced and can even be a nonmonotonic function of the gradients. Finally, in the presence of both rapid toroidal rotation and steep gradients, the transport becomes sensitive to the geometry of the magnetic equilibrium. For instance, in a single-null diverted magnetic field the ion particle flux is typically inward if the ion drift is toward the X-point and changes direction if the toroidal field is reversed.

Magnetic topology effects on Alcator C-Mod flows

“…The results given there hold in the presence of impurities (even with poloidal asymmetries due to toroidal rotation [9]), turbulence, and neutrals. Section III presents a neoclassical relation between flows of collisional high-Z trace impurities and background ions.…”

The impact of poloidal asymmetries on tungsten transport in the core of JET H-mode plasmas

“…• A reduction of the overall magnitude of the neoclassical transport, in particular, by a reduction of the usual low field side (LFS) localization of the W density produced by centrifugal (CF) effects, 7,8 which is known to produce an enhancement of the neoclassical transport. [9][10][11][12][13] This can be obtained by a reduction of the plasma toroidal rotation, or by the impact of auxiliary heating systems. In particular, ion cyclotron resonance heating (ICRH) produces a temperature anisotropy of the resonant minority species, which consequently develops a poloidally asymmetric density distribution and impacts the poloidal asymmetry of the background electrostatic potential, as well as the asymmetry of the W density.…”

Effect of poloidal asymmetries on impurity peaking in tokamaks

“…8), and their effect on neoclassical impurity transport has been discussed before. [9][10][11][12] Today there is a wealth of experimental evidence for poloidal asymmetries, for an overview of impurity asymmetry measurements organized by experiment see Ref. 13.…”