Overview of the DIII-D Negative Triangularity Campaign

In early 2023, a dedicated multi-week experimental campaign was conducted to qualify the negative triangularity (NT) scenario for future reactors on the DIII-D tokamak after the installation of graphite-tile armor on the low-field-side lower outer wall. During this campaign, high confinement (H_98y,2≥1), high current (q₉₅<3), and high normalized pressure plasmas (β_N>2.5) were achieved at high-injected-power in strongly NT-shaped plasmas with δ_avg= - 0.5 and a lower outer divertor X-point that also demonstrated high normalized density (n_e/n_GW≤2), particle confinement comparable to energy confinement, and a detached divertor without impurity seeding, all while maintaining a non-ELMing NT-edge with an electron temperature pedestal, exceeding that of typical low-confinement (L-mode) plasmas. This reactor-relevant regime is accessed over a wide range of DIII-D operational space (plasma current, toroidal field, electron density and pressure) in contrast to other high-performance non-ELMing scenarios that have narrower operating windows. Two scenarios were developed: an inductive high-gain plasma with usually lower q₉₅ and sawteeth and an advanced quasi-steady-state plasma with higher q₉₅=4 that were sawtooth-free, indicating q_min>1 was obtained.