Observation of divertor heat flux regulation by streamer-like structures in HL-2A neutral beam injection-heated H-mode plasmas

Abstract A coherent electromagnetic fluctuation with a central frequency at f ≈ 17.6 kHz has been routinely observed in HL-2A neutral beam injection-heated H-mode plasmas. This fluctuation, characterized by a radially extended structure spanning ∼23% of the minor radius without clear radial propagation, is identified as originating from broadband fluctuations (30–60 kHz) via nonlinear coupling, which is qualitatively consistent with theoretically predicated streamers [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) while reducing the divertor peak heat flux and broadening the heat flux width, indicating that these streamer-like structures have the ability to regulate the distribution of the divertor heat load by changing SOL turbulent transport. This findings presented here reveal the essential role of turbulence-driven radially extended structures in determining the divertor peak heat flux and the associated width, which may provide new insights 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 devices.