Evaluation of toroidal torque by non-resonant magnetic perturbations in tokamaks for resonant transport regimes using a Hamiltonian approach

TL;DR

This paper develops a comprehensive Hamiltonian-based method to evaluate toroidal torque caused by non-resonant magnetic perturbations in tokamaks, covering various resonant regimes and validated by numerical comparisons.

Contribution

It introduces a unified quasilinear Hamiltonian approach for all low-collisional resonant NTV regimes, including magnetic drift effects, without geometric restrictions.

Findings

The approach matches existing analytical results in the large aspect ratio limit.

Numerical simulations show magnetic drift significantly affects drift-orbit resonances.

Magnetic shear plays an important role in the magnetic drift frequency.

Abstract

Toroidal torque generated by neoclassical viscosity caused by external non-resonant, non-axisymmetric perturbations has a significant influence on toroidal plasma rotation in tokamaks. In this article, a derivation for the expressions of toroidal torque and radial transport in resonant regimes is provided within quasilinear theory in canonical action-angle variables. The proposed approach treats all low-collisional quasilinear resonant NTV regimes including superbanana plateau and drift-orbit resonances in a unified way and allows for magnetic drift in all regimes. It is valid for perturbations on toroidally symmetric flux surfaces of the unperturbed equilibrium without specific assumptions on geometry or aspect ratio. The resulting expressions are shown to match existing analytical results in the large aspect ratio limit. Numerical results from the newly developed code NEO-RT are compared to calculations by the quasilinear version of the code NEO-2 at low collisionalities. The importance of the magnetic shear term in the magnetic drift frequency and a significant effect of the magnetic drift on drift-orbit resonances are demonstrated.