担当区分：筆頭著者,　最終著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Plasma and Fusion Research  

In this study, an isentropic scaling law is developed for direct-drive implosions of solid spherical targets—a setup frequently employed in Fast Ignition Realization Experiments—in order to estimate densities at maximum compression. Adiabatic theories usually cannot explain shock-driven compression due to entropy production; however, differences among similar implosion scenarios can be approximated by isentropic laws. Numerous one-dimensional implosion simulations support for the proposed isentropic scaling law, especially regarding the relationship between confinement time and density at maximum compression.

DOI： 10.1585/pfr.21.1404018

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Computational Physics  

This paper extends the kinetic energy and entropy preserving (KEEP) scheme, which was originally designed for compressible fluid dynamics, to include compressible magnetohydrodynamics (MHD). In MHD, the magnetic energy included in the total energy equation is consistent with that derived from the induction equation. Discretizing the spatial derivative in the induction equation using the central finite difference preserves the solenoidal constraint of the magnetic field. Numerical fluxes for the momentum and the total energy related to the magnetic field can be derived for the momentum and total energy from the Lorentz force and the solenoidal constraint, even in discrete form. Numerical results confirm that the KEEP scheme enables non-dissipative and stable MHD simulations, unlike the conventional central difference method.

DOI： 10.1016/j.jcp.2025.114212

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Web of Science

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担当区分：筆頭著者,　最終著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Computational Physics  

In this paper, a conservative numerical method for the Vlasov–Darwin system is proposed. The Darwin model was assumed to be valid only in the Coulomb gauge, but recently this model has also been extended to the Lorenz gauge [1]. The Darwin model, based on the Lorenz gauge, exhibits a good symmetry between scalar and vector potentials, making the proofs of physical constraints relatively easy. In addition, the total energy was believed to be one of the conservative quantities of the Vlasov–Darwin system. However, the improved theory suggests that the Hamiltonian is the conservative quantity rather than the total energy. The structure-preserving scheme proposed in this paper exactly maintains the Lorenz gauge and the conservation laws of charge, canonical momentum, and Hamiltonian in discrete form.

DOI： 10.1016/j.jcp.2024.113267

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Computer Physics Communications  

The article describes initial steps toward the development of our nonlinear magnetohydrodynamics code, MUSES. Unstructured grids and general coordinates are employed so that MUSES code is expected to have a capability to represent realistic geometries of fusion devices. Discontinuous Galerkin method is chosen as a code framework because of its high spatial accuracy and numerical stability on unstructured grids. The governing equation of the ideal magnetohydrodynamics in this work is Powell 8-wave model which can mitigate the divergence-free issue. Roe scheme is used as a numerical flux since the Powell 8-wave model is a nonconservative system. A cross code comparison is carried out with a linear magnetohydrodynamics code, MINERVA. Owing to discontinuous Galerkin method, a linear theory of an ideal internal kink mode is reproduced quantitatively although the upwind method is employed for numerical stability.

DOI： 10.1016/j.cpc.2023.109071

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Web of Science

Scopus