Development of nonlinear extended MHD simulation technique for free boundary plasma

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K03498
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 14010:Fundamental plasma-related
• Research Institution: Tohoku University
• Principal Investigator: Hirota Makoto 東北大学, 流体科学研究所, 准教授 (40432900)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 磁気流体力学 / 自由境界問題 / 二流体プラズマ

Outline of Final Research Achievements

In the peripheral region where plasma contacts vacuum, a physically correct solution cannot be obtained by MHD, since the MHD approximation breaks down as the density decreases. In this study, we investigated a method using an extended MHD model that includes two-fluid effects in addition to the conventionally used pseudo-vacuum model. Specifically, we analyzed Z-pinch equilibrium and numerically calculated the equilibrium solution for a plasma surrounded by a vacuum region. When the plasma changes adiabatically, the interface becomes a singular surface, and we proposed a method to regularize this singularity in numerical calculation. Furthermore, in the extended MHD model, it was found that an equilibrium state cannot be obtained unless a small amount of viscosity exists in the vacuum region. Then, the extended MHD can handle free boundary problems.

Free Research Field

プラズマ物理学

Academic Significance and Societal Importance of the Research Achievements

磁場閉じ込め核融合プラズマや天体プラズマは、真空領域によって囲まれていることが多く、外側に向かって密度は徐々に下がっていく。プラズマの運動を記述する磁気流体力学(MHD)は古くから用いられてきたが、密度がゼロになると物理的に正しくなくなり、数値計算も非常に不安定になることが長年の問題となっている。本研究の成果は、MHDをより物理的に正しい形に拡張することで、真空領域を含めた数値解析が可能になることを提案しており、核融合研究や天体物理などの様々な問題に応用ができると期待される。