Insight into MHD simulation of DIII-D QH-mode saturation mechanism using power transfer analysis

Progress towards full understanding of H-mode operation regimes without edge localized modes (ELMs) requires the ability to simulate nonlinear fluctuation dynamics. Specifically, we study the dynamics of edge harmonic oscillations and broadband-MHD during DIII-D standard and wide-pedestal quiescent H-mode [Chen Nucl Fusion 2016]. The two-fluid, extended-MHD NIMROD code [Sovinec et al., J Comp Phys 2010] is used with a multispecies collisionality formulation that incorporates the carbon impurity. Fluctuations produced in nonlinear MHD simulations are dominated by low frequency and low wave numbers akin to the observed dynamics in DIII-D [Pankin et al., Phys Plasmas 2020; King et al., Phys Plasmas 2017]. The amplitude of the saturated dynamics are dependent on the amplitude of the underlying sources. As the strength of the underlying drive is varied, a spectral power-transfer diagnostic [Howell et al. Phys Plasma 2022] is applied to interpret the fluctuation saturation mechanism. A synthetic diagnostic is applied to compare the simulation with recent electron-cyclotron emission imaging measurements.