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| Format: | Preprint |
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2025
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| Online Access: | https://arxiv.org/abs/2502.01300 |
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| _version_ | 1866915421890805760 |
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| author | Park, Kiwan |
| author_facet | Park, Kiwan |
| contents | We investigated the $α$ and $β$ effects in a rotating spherical plasma system relevant to astrophysical environments. These coefficients were derived using three different approaches based on the large-scale magnetic field $\overline{\mathbf{B}}$, turbulent velocity $\mathbf{u}$, and turbulent magnetic field $\mathbf{b}$, yielding $α_{\mathrm{EM-HM}}$, $β_{\mathrm{EM-HM}}$, $β_{\mathrm{vv-vw}}$, and $β_{\mathrm{bb+jb}}$. Using raw data from direct numerical simulations (DNS), we constructed the magnetic induction equation incorporating the $α$ and $β$ coefficients. We then reproduced the $\overline{\mathbf{B}}$ field and compared the results with the DNS data. In the kinematic regime, where $\overline{\mathbf{B}}$ is weak, all models exhibit good agreement with the DNS results. However, in the nonlinear regime, the $\overline{\mathbf{B}}$ field, reproduced using $β_{\mathrm{vv-vw}}$, deviates from the DNS and exhibits unbounded growth. To address this discrepancy, we added $β_{\mathrm{bb+jb}}$, which represents the contribution of turbulent magnetic fields, to $β_{\mathrm{vv-vw}}$. This addition suppresses the divergent growth of $\overline{\mathbf{B}}$ in the nonlinear regime. We then assessed the actual influence of $α$ and $β$ on the evolution of $\overline{\mathbf{B}}$ by applying weighted combinations of the two coefficients. Our results show that magnetic $β$ diffusion plays a dominant role throughout the entire process. In contrast, the $α$ effect is minor in the kinematic regime but becomes essential for sustaining the $\overline{\mathbf{B}}$ field in the nonlinear regime. We also discussed the underlying physical mechanism responsible for this behavior. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2502_01300 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Magnetic Field Amplification and Reconstruction in Rotating Astrophysical Plasmas: Verifying the Roles of $α$ and $β$ in Dynamo Action Park, Kiwan Plasma Physics Solar and Stellar Astrophysics Space Physics We investigated the $α$ and $β$ effects in a rotating spherical plasma system relevant to astrophysical environments. These coefficients were derived using three different approaches based on the large-scale magnetic field $\overline{\mathbf{B}}$, turbulent velocity $\mathbf{u}$, and turbulent magnetic field $\mathbf{b}$, yielding $α_{\mathrm{EM-HM}}$, $β_{\mathrm{EM-HM}}$, $β_{\mathrm{vv-vw}}$, and $β_{\mathrm{bb+jb}}$. Using raw data from direct numerical simulations (DNS), we constructed the magnetic induction equation incorporating the $α$ and $β$ coefficients. We then reproduced the $\overline{\mathbf{B}}$ field and compared the results with the DNS data. In the kinematic regime, where $\overline{\mathbf{B}}$ is weak, all models exhibit good agreement with the DNS results. However, in the nonlinear regime, the $\overline{\mathbf{B}}$ field, reproduced using $β_{\mathrm{vv-vw}}$, deviates from the DNS and exhibits unbounded growth. To address this discrepancy, we added $β_{\mathrm{bb+jb}}$, which represents the contribution of turbulent magnetic fields, to $β_{\mathrm{vv-vw}}$. This addition suppresses the divergent growth of $\overline{\mathbf{B}}$ in the nonlinear regime. We then assessed the actual influence of $α$ and $β$ on the evolution of $\overline{\mathbf{B}}$ by applying weighted combinations of the two coefficients. Our results show that magnetic $β$ diffusion plays a dominant role throughout the entire process. In contrast, the $α$ effect is minor in the kinematic regime but becomes essential for sustaining the $\overline{\mathbf{B}}$ field in the nonlinear regime. We also discussed the underlying physical mechanism responsible for this behavior. |
| title | Magnetic Field Amplification and Reconstruction in Rotating Astrophysical Plasmas: Verifying the Roles of $α$ and $β$ in Dynamo Action |
| topic | Plasma Physics Solar and Stellar Astrophysics Space Physics |
| url | https://arxiv.org/abs/2502.01300 |