Improved Particle Confinement with Resonant Magnetic Perturbations in DIII-D Tokamak H-mode Plasmas

Experiments on the DIII-D tokamak have identified a robust regime in which applied resonant magnetic perturbations (RMPs) increase the particle confinement while partially stabilizing the edge-localized peeling modes. RMPs are of interest for the control the rotational shear and/or suppression of edge localized modes (ELMs) for reactor relevant scenarios, however they have hitherto been observed to degrade the particle confinement via the density "pump-out" phenomenon. This work details DIII-D experiments and model calculations showing the surprising result that there is a range of counter-current plasma rotation (induced by neutral beam injection in the direction opposite to the plasma current) where the 3D fields instead increase the particle confinement, resulting in a particle "pump-in" effect. The new density pump-in phenomenon corresponds to a change in the sign of neoclassical particle transport across flux surfaces induced by the toroidal symmetry breaking, as modeled by the Generalized Perturbed Equilibrium Code (GPEC). The pump-in is also preceded by a decrease in the turbulent fluctuation (and presumed turbulent transport) as evidenced by the prompt drop in microwave doppler back scattering measurements of edge ion-scale density fluctuations. The rise in density also corresponds to lower frequency ELMs, however the change in the ELM frequency and amplitude is such that the time-average ELM induced particle transport is unchanged. The full combination of observed phenomena is robust and reproducible across a finite range of counter-Ip rotation (-80 to 0 km/s) in the pedestal top of DIII-D. This pump-in regime has the potential to minimize or even reverse the confinement degradation currently observed in RMP H-mode scenarios. Implications for ITER and fusion reactors will be discussed.