DIII-D experiments show RMPs reversing neoclassical transport to raise core density in H-mode

The DIII-D team applied n=3 RMPs across a range of toroidal rotation values and measured a robust density pump-in for counter-current flows below roughly 20 krad/s. Density profile evolution and fluctuation diagnostics indicated reduced turbulent particle flux while neoclassical modeling showed the E_r shear change reversed the direction of the RMP-driven neoclassical pinch. The net result raised stored energy and confinement time without degrading the H-mode pedestal. This regime directly addresses the long-standing tension between ELM control and particle exhaust in reactor-scale devices. Because the effect scales with the RMP-induced neoclassical torque rather than stochastic layer width, it may persist at the lower rotation expected in ITER and DEMO. The finding therefore reframes RMPs from a necessary penalty to a potential optimization tool for three-dimensional confinement.