Observation of divertor heat flux regulation by the streamer-like structures in HL-2A NBI-heated H-mode plasmas

A coherent electromagnetic fluctuation with a central frequency at f ≈ 17.6 kHz has been routinely observed in HL-2A NBI-heated H-mode plasmas. This fluctuation, characterized by a radially extended structure, spanning ~23% of the minor radius without a clear radial propagation, is identified as originating from the broadband fluctuations (30-60 kHz) via the nonlinear coupling, which is qualitatively consistent with the theoretically-predicated streamers [G. Manfredi et al 2001 Plasma Phys. Control. Fusion 43 825]. Further analysis demonstrates that such structures could enhance radial heat transport in the scrape-off layer (SOL), meanwhile reduce the divertor peak heat flux and broaden the heat flux width, indicating that the streamer-like structures have an ability to regulate the distribution of divertor heat load through changing the SOL turbulent transport. This finding presented here reveals the essential role of turbulence-driven radially-extended structures in determining the divertor peak heat flux and the associated width, which may provide new insight for the mitigation of plasma-material interaction and the optimization of divertor performance via the control of SOL turbulent transport in future magnetic confinement fusion device.