The stabilization of a small-scale dynamo caused by a change in the energy spectrum of a conducting plasma flow is investigated. Such a change in kinetic properties can be due to the reverse conversion of generated magnetic energy into kinetic energy. We model the reverse conversion process using the classical Kazantsev model, which describes the operation of a small-scale dynamo in a mirror-symmetric turbulent flow. Our results suggest that the appearance of magnetic energy at small scales in the kinetic spectrum can stop the generation process. This stabilization turns out to be no less efficient than the braking of a turbulent dynamo through the conservation of total magnetic and kinetic energies. However, it looks more realistic, because for most dynamo systems the observed magnetic energy is lower than the kinetic one by several orders of magnitude. We show that in this method of nonlinear suppression just the appearance of energy at small scales is often not enough; in particular, a simple shift of the Gaussian spectrum toward small scales only amplifies the generation. In this paper, we describe a reasonable spectrum transformation method that allows the generation in both critical and supercritical regimes of small-scale dynamo operation to be stabilized. The fact that the described spectrum transformation can be directly recorded in an experimental test is equally important.
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The work of D.D.S. and A.S.L. on the formulation of the problem and the search for methods of its solution was supported by the Russian Foundation for Basic Research (project no. 18-02-00085). The numerical experiment carried out by E.V.Yu. and the interpretation of results by all authors were supported by the BAZIS Foundation (project no. 18-1-1-77-3).
Translated by V. Astakhov
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Yushkov, E.V., Lukin, A.S. & Sokoloff, D.D. Suppression of Small-Scale Magnetic Field Generation by Transformation of the Kinetic Energy Spectrum. J. Exp. Theor. Phys. 129, 1086–1093 (2019). https://doi.org/10.1134/S1063776119110189