Orbital Spectrum Analysis of Non-Axisymmetric Perturbations of the Guiding-Center Particle Motion in Axisymmetric Equilibria

TL;DR

This paper introduces the Orbital Spectrum Analysis (OSA) method, which semi-analytically identifies resonant spectral components of non-axisymmetric perturbations affecting particle motion in axisymmetric magnetic fields, accounting for finite orbit widths.

Contribution

The paper presents a novel OSA method based on an exact Action-Angle transform that fully incorporates Finite Orbit Width effects for analyzing particle dynamics under perturbations.

Findings

Exact locations and strengths of resonant spectral components calculated.

OSA provides insights into particle dynamics and perturbation effects.

Method applicable to both analytical and numerical equilibria.

Abstract

The presence of non-axisymmetric perturbations in an axisymmetric magnetic field equilibrium renders the Guiding Center (GC) particle motion non-integrable and may result in particle, energy and momentum redistribution, due to resonance mechanisms. We analyse these perturbations in terms of their spectrum, as observed by the particles in the frame of unperturbed GC motion. We calculate semi-analytically the exact locations and strength of resonant spectral components of multiple perturbations. The presented Orbital Spectrum Analysis (OSA) method is based on an exact Action-Angle transform that fully takes into account Finite Orbit Width (FOW) effects. The method provides insight into the particle dynamics and enables the prediction of the effect of any perturbation to all different types of particles and orbits in a given, analytically or numerically calculated, axisymmetric equilibrium.