Numerical Demonstration of Fluctuation Dynamo at Low Magnetic Prandtl Numbers

Direct numerical simulations of incompressible nonhelical randomly forced MHD turbulence are used to demonstrate for the first time that the fluctuation dynamo exists in the limit of large magnetic Reynolds number Rm≫1 and small magnetic Prandtl number Pm≪1. The dependence of the critical Rm_c for dynamo on the hydrodynamic Reynolds number Re is obtained for 1≲Re≲6700. In the limit Pm≪1, Rm_c is about 3 times larger than for the previously well-established dynamo at large and moderate Prandtl numbers: Rm_c≲200 for Re≳6000 compared to Rm_c∼60 for Pm≥1. It is not yet possible to determine numerically whether the growth rate of the magnetic energy is ∝Rm^1/2 in the limit Rm→∞, as it should be if the dynamo is driven by the inertial-range motions at the resistive scale.