Shifting and splitting of resonance lines due to dynamical friction in plasmas

TL;DR

This paper develops a quasilinear plasma transport theory incorporating dynamical friction, revealing how drag causes resonance line shifting and splitting, significantly affecting particle redistribution in plasmas and galactic systems.

Contribution

It introduces a self-consistent quasilinear model that includes dynamical friction, showing its impact on resonance structures and particle redistribution, validated against nonlinear simulations.

Findings

Drag causes resonance line shifting and splitting.

Scattering broadens resonance symmetrically.

Model matches nonlinear simulation results.

Abstract

A quasilinear plasma transport theory that incorporates Fokker-Planck dynamical friction (drag) and pitch angle scattering is self-consistently derived from first principles for an isolated, marginally-unstable mode resonating with an energetic minority species. It is found that drag fundamentally changes the structure of the wave-particle resonance, breaking its symmetry and leading to the shifting and splitting of resonance lines. In contrast, scattering broadens the resonance in a symmetric fashion. Comparison with fully nonlinear simulations shows that the proposed quasilinear system preserves the exact instability saturation amplitude and the corresponding particle redistribution of the fully nonlinear theory. Even in situations in which drag leads to a relatively small resonance shift, it still underpins major changes in the redistribution of resonant particles. This novel influence of drag is equally important in plasmas and gravitational systems. In fusion plasmas, the effects are especially pronounced for fast-ion-driven instabilities in tokamaks with low aspect ratio or negative triangularity, as evidenced by past observations. The same theory directly maps to the resonant dynamics of the rotating galactic bar and massive bodies in its orbit, providing new techniques for analyzing galactic dynamics.