Universal growth of magnetic energy during the nonlinear phase of subsonic and supersonic small-scale dynamos.
basic_science · Level V
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- Record sourced from PubMed, PMID 42141599.
- Also identified by DOI 10.1103/8qjf-8gg4.
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Abstract
Small-scale dynamos (SSDs) amplify magnetic fields in turbulent plasmas. Theory predicts nonlinear magnetic energy growth E_{mag}∝t^{p_{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_{nl}=1) in subsonic flows and quadratic growth (p_{nl}=2) in supersonic flows. In all cases, the nonlinear dynamo converts a nearly constant fraction approximately equal to 1/100 of the turbulent kinetic energy flux into magnetic energy, and the nonlinear phase has a characteristic duration Δt≈20t_{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.