Scrape-off layer power fall-off length broadening in H-mode with reduced negative triangularity on DIII-D

Small ELM regimes are viewed as promising scenarios for managing the core-edge integration challenge via reducing the transient heat loads typical of type-I ELMy scenarios while simultaneously avoiding any large reductions in core performance. One such regime is negative triangularity H-modes at reduced shaping, i.e. reduced NT H-mode, which generally have near zero, but positive lower triangularity and negative upper triangularity no greater than −0.1. This reduced NT H-mode regime has similar stored energy values to standard type-I regimes for the relatively low pedestal height while displaying the characteristics of small ELMs: reduced energies delivered to the divertor, lower peak heat flux amplitudes, and higher frequencies than the standard type-I ELMs. Moreover the correlation between these reduced NT H-modes’s $\lambda_{q}$ broadening beyond the $B_{pol}^(-1)$ scaling and with reduced rotation shear indicate a favorable path for achieving a core-edge solution with higher stored energy while reducing the normalized ELM size and broadening the heat flux profile. All these characteristics make it a promising regime for a future fusion reactor.