Alpha-unstable flows and the fast dynamo problem
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arXiv
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| Autori principali: | , , |
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| Natura: | Preprint |
| Pubblicazione: |
2025
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| _version_ | 1866912303919661056 |
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| author | Zelati, Michele Coti Sorella, Massimo Villringer, David |
| author_facet | Zelati, Michele Coti Sorella, Massimo Villringer, David |
| contents | We construct a time-independent, incompressible, and Lipschitz-continuous velocity field in $\mathbb{R}^3$ that generates a fast kinematic dynamo - an instability characterized by exponential growth of magnetic energy, independent of diffusivity. Specifically, we show that the associated vector transport-diffusion equation admits solutions that grow exponentially fast, uniformly in the vanishing diffusivity limit $\varepsilon\to 0$. Our construction is based on a periodic velocity field $U$ on $\mathbb{T}^3$, such as an Arnold-Beltrami-Childress flow, which satisfies a generic spectral instability property called alpha-instability, established via perturbation theory. This provides a rigorous mathematical framework for the alpha-effect, a mechanism conjectured in the late 1960s to drive large-scale magnetic field generation. By rescaling with respect to $\varepsilon$ and employing a Bloch-type theorem, we extend the solution to the whole space. Finally, through a gluing procedure that spatially localizes the instability, we construct a globally defined velocity field $u$ in $\mathbb{R}^3$ that drives the dynamo instability. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2504_00855 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Alpha-unstable flows and the fast dynamo problem Zelati, Michele Coti Sorella, Massimo Villringer, David Analysis of PDEs 35Q35 We construct a time-independent, incompressible, and Lipschitz-continuous velocity field in $\mathbb{R}^3$ that generates a fast kinematic dynamo - an instability characterized by exponential growth of magnetic energy, independent of diffusivity. Specifically, we show that the associated vector transport-diffusion equation admits solutions that grow exponentially fast, uniformly in the vanishing diffusivity limit $\varepsilon\to 0$. Our construction is based on a periodic velocity field $U$ on $\mathbb{T}^3$, such as an Arnold-Beltrami-Childress flow, which satisfies a generic spectral instability property called alpha-instability, established via perturbation theory. This provides a rigorous mathematical framework for the alpha-effect, a mechanism conjectured in the late 1960s to drive large-scale magnetic field generation. By rescaling with respect to $\varepsilon$ and employing a Bloch-type theorem, we extend the solution to the whole space. Finally, through a gluing procedure that spatially localizes the instability, we construct a globally defined velocity field $u$ in $\mathbb{R}^3$ that drives the dynamo instability. |
| title | Alpha-unstable flows and the fast dynamo problem |
| topic | Analysis of PDEs 35Q35 |
| url | https://arxiv.org/abs/2504.00855 |