Multi-species extended MHD simulations of ELM-free negative triangularity DIII-D plasmas and the CETOP SciDAC project

Recent developments of ELM-free negative triangularity (NT) regimes via plasma shaping have exhibited interesting edge MHD dynamics. Here, we have performed global simulations for strongly shaped NT DIII-D discharges with low (193754, 193755) and high beta (193843). We model the entire plasma, including the core, edge, SOL and vacuum regions. Unlike in ELMing DIII-D PT simulations, where the nonlinear mode coupling of intermediate-n PB modes causes reconnection-mediated ELM crash, here we obtain ELM-free NT states. Using multi-species collisionality, our 2-fluid NIMROD simulations of two strongly-shaped NT plasmas in DIII-D show a persistent slow-growing reconnecting n=1 mode consistent with the experiment [T. Cote et al. Plasma Phys. Control. Fusion 67 035033, 2025]. For a high beta plasma, nonlinear simulations show relaxation of plasma current via a two-fluid core dynamo effect. We also compare our results with a weakly-shaped NT plasma. Some highlights of our CETOP (Center for Edge of Tokamak OPtimization) project will also be presented. This work was supported by the DOE SciDAC program under Award Numbers DE-AC02-09CH11466, DE-FC02-04ER54698, DE-SC0023500, DE-SC0022270 and DE-SC0024592.