Analytical calculation of the kinetic q factor and resonant response of toroidally confined plasmas

TL;DR

This paper presents an analytical method to calculate the kinetic q factor in toroidal plasmas, enabling prediction of resonant interactions and transport barriers, validated against numerical simulations for large aspect ratio configurations.

Contribution

It introduces a semi-analytical approach to determine the kinetic q factor and resonant structures, enhancing understanding of plasma response to perturbations with low computational cost.

Findings

Analytical calculation of the kinetic q factor matches numerical simulations.

Identification of resonant island-chains and transport barriers.

Method applicable to realistic experimental equilibria.

Abstract

Symmetry-breaking perturbations in axisymmetric toroidal plasma configurations have a drastic impact on particle, energy, and momentum transport in fusion devices, thereby affecting their confinement properties. The perturbative modes strongly affect particles with specific kinetic characteristics through resonant mode-particle interactions. In this work we present an analytical calculation of the kinetic q factor enabling the identification of particles with kinetic properties that meet the resonant conditions. This allows us to predict the locations and structures of the corresponding resonant island-chains, as well as the existence of transport barriers in the particle phase space. The analytical results, derived for the case of a large aspect ratio configuration, are systematically compared to numerical simulations, and their domain of validity is thoroughly investigated and explained. Our findings demonstrate that calculating the kinetic q factor and its dependence on both particle and magnetic field characteristics, provides a valuable tool for understanding and predicting the resonant plasma response to non-axisymmetric perturbations. Moreover, this approach can be semi-analytically applied to generic realistic experimental equilibria, offering a low-computational-cost method for scenario investigations under various multiscale perturbative modes.