Neoclassical transport due to resonant magnetic perturbations in DIII-D and NSTX

Resonant magnetic perturbations (RMPs) are applied to mitigate or suppress the instabilities present in the plasma called edge localized modes (ELMs) which arise because of the steep pressure gradient at the edge in H-mode plasmas. The RMPs often result in a decrease in the plasma density, also referred to as density pump-out, which adversely affects the fusion performance. In this study, the role of neoclassical transport in density pump-out and heat flux in the presence of RMPs is investigated in DIII-D and NSTX plasmas. The drift kinetic code NEO with the enhanced capability to handle non-axisymmetric magnetic geometry is used here to evaluate the neoclassical transport properties where RMPs are applied. The magnetic field provided as an input to NEO is calculated using extended magnetohydrodynamic code M3D-C1 and includes the nonlinear resistive plasma response in realistic geometry and with realistic values of resistivity. The study performed here indicates a dramatic increase of the neoclassical particle and energy fluxes for main ions in the presence of the RMPs and is on the same order as experimentally inferred fluxes, suggesting that neoclassical transport plays an important role in edge transport in such cases. The calculated neoclassical fluxes in DIII-D plasmas are found to be closely correlated with the observations of density pump-out over a range of RMP spectra. These calculations show that nonlinear MHD simulations are essential at high RMPs to satisfactorily model the perturbed magnetic geometry in the pedestal region. The study of transport dynamics of impurities is important as they can lead to fuel dilution, radiative cooling which deteriorates the plasma performance, and has also been analyzed using this framework. Our study indicates that the atomic number (Z), collisionality of the impurity and perturbation field strength determines the effect of RMPs on neoclassical impurity transport. We extrapolate our results to further predict the impurity transport and its control in ITER.