Resonant Excitation of Shear Alfv\'en Perturbations by Trapped Energetic Ions in a Tokamak

TL;DR

This paper develops a new non-perturbative analytic theory for resonant excitation of high-n shear Alfvén modes by energetic ions in tokamaks, incorporating finite orbit effects and aligning with experimental observations.

Contribution

It introduces a novel analytic expression for resonant mode drive that includes finite orbit effects and applies to Alfvén cascade modes, advancing the theoretical understanding.

Findings

Predictions align with JET experimental data.

Complete theory of downward sweeping Alfvén cascade modes.

Explicit calculation of particle response integrals.

Abstract

A new analytic expression is derived for the resonant drive of high n Alfvenic modes by particles accelerated to high energy by Ion Cyclotron Resonance Heating. This derivation includes finite orbit effects, and the formalism is completely non-perturbative. The high-n limit is used to calculate the complex particle response integrals along the orbits explicitly. This new theory is applied to downward sweeping Alfven Cascade quasimodes completing the theory of these modes, and making testable predictions. These predictions are found to be consistent with experiments carried out on the Joint European Torus [P. H. Rebut and B. E. Keen, Fusion Technol. 11, 13 (1987)].