H-mode pedestal performance in high triangularity, high elongation, high plasma current discharges on DIII-D

The first phase of a 5-year program on DIII-D to study and optimize core-edge integration at more FPP relevant conditions was completed in 2025. The upper divertor was modified to allow pumping at high triangularity, elongation and plasma current (δ=0.93, κ=2, , I_P=2.2MA), with the goal of producing high pedestal pressure at high density in the Super-H-mode regime, and move towards the low collisionality, shallow neutral penetration pedestals expected in an FPP. Three approaches were taken : ELMy, Quiescent and RMP ELM-suppressed H-mode. ELMy H-modes resulted in the highest pedestal pressure and core performance observed to date in DIII-D: P_PED=37kJ, β_N-PED=1.4, W=2.4MJ, <P>τ_E/(I_PaB_T)=11, DT equivalent fusion gain~0.2, which persisted for several ELM cycles but ultimately ended in an ELM-triggered global energy loss. The QH-mode discharges also entered Super-H-mode, but did not reach the same performance; however, the ELM-initiated global collapse was avoided. QH-mode persisted as the density was raised, with a shift from peeling to ballooning limited pedestal, as a result of the strong shaping. Combining RMP ELM suppression with Super-H-mode was only achieved at higher q₉₅=7.5, and so low absolute pedestal performance, as inboard plasma response weakens in the near-double-null shape that favors SH access. Pedestal width in these experiments did not conform to the EPED1 width scaling typical of DIII-D discharges w = 0.089(β_POL-PED)^1/2 in some cases exceeding this scaling by more than a factor of 2. Widths instead were found to be consistent with n=60 ballooning mode critical gradient as a proxy for the KBM. A weaker correlation was also noted between the EPED1 width scaling coefficient and the density gradient scale length or η_e.