Analysis of energetic particle transport: diffusion and phase-space barriers

TL;DR

This paper presents a detailed phase-space and statistical analysis of energetic particle transport, revealing complex dynamics beyond simple diffusion and highlighting limitations of quasi-linear models in describing turbulent transport.

Contribution

It introduces a comprehensive analysis of transport regimes in a reduced model, emphasizing the complex resonance interactions and avalanche phenomena in energetic particle dynamics.

Findings

Deviations from normal diffusive behavior are quantitatively demonstrated.

Complex resonance overlapping and substructure formation are observed.

Evidence of avalanche excitation and inter-mode energy transfer is reinforced.

Abstract

A reduced 1D model describing the non-linear hybrid LIGKA/HAGIS simulations was developed and successfully tested in [Carlevaro et al. PPCF 64, 035010 (2022)] addressing the ITER 15MA baseline scenario. In this paper, we introduce a detailed phase-space and statistical analysis to characterize the emerging transport regimes. Deviations from purely normal diffusive dynamics is quantitatively analyzed, indicating the limitations of the usual quasi-linear description of energetic particle turbulent transport. Beside the emergence of a very complex dynamics of overlapping resonances and substructure formation, this analysis reinforces the evidence of avalanche excitation and energy transfer between modes.