AE-driven Zonal Modes Produce Transport Barriers and Heat Thermal Ions by Cross-Scale Interactions

TL;DR

This paper presents a novel theory where energetic particle-driven Alfvén eigenmodes generate zonal modes through cross-scale interactions, leading to transport barriers and heat transfer mechanisms in plasma confinement.

Contribution

It introduces a new self-regulating TAE-zonal mode interaction framework that explains transport barrier formation and thermal ion heating in plasma physics.

Findings

Zonal modes driven by Reynolds and Maxwell stresses without modulational instability.

Saturated zonal shears can suppress drift-ITG turbulence, improving confinement.

Alpha particle energy is transferred to thermal plasma via zonal mode damping.

Abstract

In scenarios where a sustained energetic particle source strongly drives toroidal Alfv\'en eigenmodes (TAE), and phase-space transport is insufficient to saturate TAE, this novel theory of TAE-zonal mode (ZM)-turbulence -- self-regulated by cross-scale interactions (including collisionless ZF damping) -- merits consideration. Zonal modes are driven by Reynolds and Maxwell stresses, without the onset of modulational instability. TAE evolution in the presence of ZMs conserves energy and closes the system feedback loop. The saturated zonal shears can be sufficient to suppress ambient drift-ITG turbulence, achieving an enhanced core confinement regime. The necessary mechanism is identified. The saturated state is regulated by linear and turbulent zonal flow drag. This regulation leads to bursty TAE spectral oscillations, which overshoot while approaching saturation. Heating by both collisional and collisionless ZM damping deposits alpha particle energy into the thermal plasma, achieving effective alpha channeling. This theory offers a mechanism for EP-induced transport barrier formation, and predicts a novel thermal ion heating mechanism.