A broadband reversal of the fluctuation-induced radial particle flux, specifically a transition from outward to inward, is observed at the edge of HL-2A L-mode plasmas during sustained neutral beam injection heating. This transition is driven by a systematic synchronization of the cross-phase between density and radial velocity fluctuations, rather than by changes in their amplitudes. Spectral analysis identifies the dominant role of low-frequency turbulence (), which exhibits contracting wavenumber spectra and extended correlation lengths, indicating self-organization into large-scale coherent structures. The inward flux is quantitatively linked to two key momentum-related parameters: a marked increase in the coherence of the Reynolds stress at low frequencies, and a near-linear dependence on the radial velocity gradient beyond a threshold of . These findings are consistent with the dual cascade picture of two-dimensional turbulence, in which energy inversely cascades to form large-scale coherent structures that drive the inward flux, while enstrophy is transferred forward to smaller scales where it is dissipated. The concomitant observation of enhanced cross-scale coherence, further underscores the importance of multi-scale coupling in this self-organization process. This work establishes a direct connection between turbulent self-organization across multiple scales and the reversal of edge particle transport, offering new insights for transport control in fusion plasmas.
Multi-scale self-organisation of edge plasma turbulent transport in 3D global simulations