Modeling of QH-mode DIII-D plasmas with an extended MHD code*

The wide-pedestal (WP) QH-mode is an operational regime with increased pedestal height and thermal energy confinement compared to the standard QH-mode, with a wider pedestal than the EPED prediction [Burrell et al., PoP 23, 056103 (2016), Chen et al., NF 57, 022007 (2017), Snyder et al., NF 51, 103016 (2011)]. The WP QH-mode can be accessed/sustained with zero net torque [Burrell et al., NF 60, 086005 (2020)], which is essential to its exploitation for future devices. To extrapolate this regime to future fusion reactors, a detailed understanding of its underlying physics is needed. Due to the high level of impurity [Darin et al., APS-DPP 2023], the self-consistent interaction between impurities and WP QH-mode requires investigation. Previous work showed the stabilizing effect of impurities on pedestal modes in WP QH-mode plasmas [Li et al., NF 62, 076033 (2022)]. Here we present nonlinear MHD simulations with the extended full-MHD code NIMROD that includes 2-fluid/FLR effects and full-Braginskii collisionality with impurity effects and anisotropic closures [Sovinec et al., JCP 229, 5803 (2010), King et al., APS-DPP (2022)]. NIMROD obtains field-aligned pedestal tearing modes and non field-aligned electrostatic modes. The power transfer analysis [Howell et al., PoP 29, 022507 (2022)] clarifies the mode saturation mechanism. Comparison between simulation results and experiments is discussed. Work supported by US DOE under grants DE-SC0024592, DE-FC02-04ER54698, DE-AC02-09CH11466 and DE-SC0022270.