The universal growth of magnetic energy during the nonlinear phase of subsonic and supersonic small-scale dynamos
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arXiv
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| Auteurs principaux: | , , , , |
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| Format: | Preprint |
| Publié: |
2025
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| _version_ | 1866911634095603712 |
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| author | Kriel, Neco Beattie, James R. Krumholz, Mark R. Schober, Jennifer Armstrong, Patrick J. |
| author_facet | Kriel, Neco Beattie, James R. Krumholz, Mark R. Schober, Jennifer Armstrong, Patrick J. |
| contents | Small-scale dynamos (SSDs) amplify magnetic fields in turbulent plasmas. Theory predicts nonlinear magnetic energy growth $E_\mathrm{mag} \propto t^{p_\mathrm{nl}}$, but this scaling has not been tested across flow regimes. Using a large ensemble of SSD simulations spanning subsonic to supersonic turbulence, we measure linear growth ($p_\mathrm{nl} = 1$) in subsonic flows and quadratic growth ($p_\mathrm{nl} = 2$) in supersonic flows. In all cases, the nonlinear dynamo converts a nearly constant fraction $\sim 1/100$ of the turbulent kinetic energy flux into magnetic energy, and the nonlinear phase has a characteristic duration $Δt \approx 20\,t_0$, where $t_0$ is the outer-scale turnover time. By isolating the onset of magnetic backreaction in SSDs, our statistical ensemble approach identifies a robust efficiency and duration for the nonlinear SSD that can be used to interpret more complex astrophysical and laboratory plasmas. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2509_09949 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | The universal growth of magnetic energy during the nonlinear phase of subsonic and supersonic small-scale dynamos Kriel, Neco Beattie, James R. Krumholz, Mark R. Schober, Jennifer Armstrong, Patrick J. Plasma Physics Computational Physics Small-scale dynamos (SSDs) amplify magnetic fields in turbulent plasmas. Theory predicts nonlinear magnetic energy growth $E_\mathrm{mag} \propto t^{p_\mathrm{nl}}$, but this scaling has not been tested across flow regimes. Using a large ensemble of SSD simulations spanning subsonic to supersonic turbulence, we measure linear growth ($p_\mathrm{nl} = 1$) in subsonic flows and quadratic growth ($p_\mathrm{nl} = 2$) in supersonic flows. In all cases, the nonlinear dynamo converts a nearly constant fraction $\sim 1/100$ of the turbulent kinetic energy flux into magnetic energy, and the nonlinear phase has a characteristic duration $Δt \approx 20\,t_0$, where $t_0$ is the outer-scale turnover time. By isolating the onset of magnetic backreaction in SSDs, our statistical ensemble approach identifies a robust efficiency and duration for the nonlinear SSD that can be used to interpret more complex astrophysical and laboratory plasmas. |
| title | The universal growth of magnetic energy during the nonlinear phase of subsonic and supersonic small-scale dynamos |
| topic | Plasma Physics Computational Physics |
| url | https://arxiv.org/abs/2509.09949 |