Study Of Alfven Eigenmodes Stability In Plasma With Multiple Nbi Driven Energetic Particle Species

The aim of this study is to analyze the destabilization of Alfven Eigenmodes (AEs) by multiple energetic particle (EP) species in DIII-D and LHD discharges. We use the reduced MHD equations to describe the linear evolution of the poloidal flux and the toroidal component of the vorticity in a full 3D system, coupled with equations of density and parallel velocity moments for the energetic particle species, including the effect of the acoustic modes, diamagnetic currents, and helical couplings. We add the Landau damping and resonant destabilization effects using a closure relation. The simulations with multiple neutral beam injector (NBI) lines show three different regimes: the nondamped regime where the multibeam AE growth rate is larger compared to the growth rate of the AEs destabilized by the individual NBI lines, the interaction regime where the multibeam AE growth rate is smaller than the single NBI AEs, and the damped regime where the AEs are suppressed. Operations in the damped regime require EP species with different density profile flatness or gradient locations. In addition, the AE growth rate in the interaction regime is further reduced if the combined NBI lines have similar beam temperatures and the beta of the NBI line with a flatter EP density profile increases. Then, optimization trends are identified in DIII-D high poloidal beta and LHD low density/magnetic field discharges with multiple NBI lines as well as the configuration requirements to operate in the damped and interaction regimes. DIII-D simulations show a decrease in the n=2 to 6 AE growth rate and n=1 AE are stabilized in the LHD case. The helical coupling effects in LHD simulations lead to a transition from the interaction to the damped regime of the n=2, -8, 12 helical family.