Dynamical Quenching of the α2Dynamo
| Autor: | George B. Field, Eric G. Blackman |
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| Rok vydání: | 2002 |
| Předmět: | |
| Zdroj: | The Astrophysical Journal. 572:685-692 |
| ISSN: | 1538-4357 0004-637X |
| DOI: | 10.1086/340233 |
| Popis: | We present a two-scale approximation for the dynamics of a nonlinear $\alpha^2$ dynamo. Solutions of the resulting nonlinear equations agree with the numerical simulations of Brandenburg (2001), and show that $\alpha$ is quenched by the buildup of magnetic helicity at the forcing scale $1/k_2$ as the $\alpha$ effect transfers it from the large scale $1/k_1$. For times $t > (k_1/k_2)R_{M,2}$ in eddy turnover units (where $R_{M,2}$ is the magnetic Reynolds number of the forcing scale), $\alpha$ is resistively limited in the form predicted for the steady-state case. However, for $t << R_{M,2}$, $\alpha$ takes on its kinematic value, independent of $R_{M,2}$, allowing the production of large-scale magnetic energy equal to $k_1/k_2$ times equipartition. Thus the dynamic theory of $\alpha$ predicts substantial "fast" growth of large-scale field despite being "slow" at large times. Comment: significantly revised, 21 pages, 6 new figs (figs. 1-5 in text, fig. 6 is separate), submitted to ApJ |
| Databáze: | OpenAIRE |
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