Broadening of scrape-off layer width by turbulence spreading in the heavy hydrogen isotope plasmas

A significant enhancement of turbulence spreading across the last closed flux surface (LCFS) has been observed during the transition from hydrogen (H)- to deuterium (D)-dominated plasmas in the HL-2A tokamak. Experimental results show that boundary turbulence increases in D plasmas compared to H plasmas, while the E × B shear flow in the vicinity of the LCFS is accordingly reduced. It is found that fluctuations inside the LCFS are dominated by interchange turbulence, which spreads radially outward and penetrates the LCFS into the scrape-off layer (SOL), leading to a broader SOL width and a reduction of parallel heat flux. These findings highlight the significant contribution from turbulence spreading to the broadening SOL width and suggest a promising strategy for controlling exhaust heat load while maintaining good plasma confinement through isotope mass optimization in future fusion reactors.