Global Gyrokinetic Simulations of Isotope Effects under Ambipolar Electric Fields and Advances Toward Whole-Volume Modeling

We review global gyrokinetic simulation studies on plasma transport in the Large Helical Device using XGC-S. XGC-S is an extended version of X-point Gyrokinetic Code for stellarators and has been progressively verified throughout the code development process. Verification tests of neoclassical transport successfully demonstrate the generation of an ambipolar electric field due to ripple-trapped particles. We perform quasi-linear analyses of the ion temperature gradient mode under the influence of the ambipolar electric field. The results reveal that the ambipolar electric field and the heavy hydrogen component in mixed isotope plasmas can lead to the favorable isotope effect observed in recent deuterium experiments. We also present recent efforts in code development toward whole-volume simulations, including the helical divertor region. A mesh generation scheme based on field-line tracing and the construction of curved surfaces perpendicular to the magnetic field would be promising for global field calculations in the whole-volume simulations.. Authors: Moritaka, Toseo [National Institute for Fusion Science, Gifu (Japan); The Graduate University for Advanced Studies (SOKENDAI), Gifu (Japan)]; Hager, Robert [Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)] (ORCID:0000000246243150); Sugama, Hideo [National Institute for Fusion Science, Gifu (Japan); Univ. of Tokyo (Japan)]; Satake, Shinsuke [National Institute for Fusion Science, Gifu (Japan)]; Matsuoka, Seikichi [National Institutes for Quantum Science and Technology, Ibaraki (Japan)]. DOE Contract: AC02-09CH11466. Subjects: Basic Plasma Phenomena and Gas Discharges; Global gyrokinetic simulation; High Temperature Plasma; Isotope effect; Magnetospheric Physics; Neoclassical and turbulent transports; Numerical Simulation; Plasma Physics; Radial electric field; Waves, instabilities and nonlinear plasma dynamics; Whole-volume modeling