Energetic particle transport: diffusion vs convection and phase-space barriers

TL;DR

This paper investigates energetic particle transport in fusion plasmas, comparing diffusion and convection mechanisms, and identifies phase-space barriers using advanced modeling and Lagrangian Coherent Structures techniques.

Contribution

It introduces a simplified 1D model to classify transport as convective or diffusive and applies Lagrangian Coherent Structures to study phase-space barriers.

Findings

Transport can be dominated by avalanches under certain conditions.

The 1D model effectively reproduces complex transport phenomena.

Phase-space barriers are identified using Lagrangian Coherent Structures.

Abstract

Energetic particle redistribution in the presence of multiple Alfv\'en eigenmodes is analyzed in [PPCF 58, 014019 (2016)] for the ITER 15MA baseline scenario: non-linear hybrid simulations (within their well known limits) point out that transport can be dominated by avalanches under certain conditions. These phenomena are properly reproduced by the 1D reduced description of [PPCF 64, 035010 (2022)]. Here, using this simplified 1D model, we define the transport character (convective/diffusive) of self-consistent energetic particle redistribution. Transport barriers in phase space are studied using the Lagrangian Coherent Structures technique.