Negative triangularity plasmas in DIII-D and their potential for core-edge integration

In DIII-D, discharges with negative triangularity (NegD) shaping (δ_u~-0.4) display H-mode-like confinement (H_98,y2~1, β_N~3) without ELMs or a pedestal with input power P_INJ up to 14MW (~4xP_LH). Improved confinement with respect to positive triangularity L-mode is due to reduced turbulent transport while ballooning mode destabilization prevents H-mode access. Poor core impurity confinement is observed with confinement times τ_Z<100ms. NegD discharges display L-mode like edge n_e gradients and edge T_e gradients intermediate between L and H-mode, with SOL power widths (λ_q) in NegD L-mode discharges up to 50% wider than in H-mode plasmas. While dissipative regimes were not explored experimentally, fluid simulations (SOLPS, UEDGE) with P_SOL~5 MW identified a window of detachment access without impurity seeding. The wider λ_q and weak density peaking are expected to be beneficial for detachment access at low average n_e while improving detachment controllability. L-mode operation at high P_INJ and short τ_Z can enable scenarios with high core radiation fraction, easing requirements on divertor dissipation, with the potential to provide an integrated core-edge solution for a fusion power plant.