Abstract

with L. Petitdemange, C.Gissinger and F.Marcotte Dynamo action in a stably stratified regime have long been investigated both numerically and theoretically for modelling MHD astrophysical objects such as stars, but it’s only recently that such a regime could be found by running Direct Numerical Simulations. The so-called Tayler-Spruit dynamo interestingly maintains a magnetic field by generating a source of turbulence in the stable region, and this is even done below know thresholds of hydrodynamical instabilities. We investigate the subcritical nature of this dynamo in terms of fluctuations and prove that it relies on a constant magnetic Reynolds number if the rotation and stratification are fixed. Isolating the key dynamical modes we propose a low dimensional model reproducing this subcriticality involving only three modes, highlighting the interaction between hydrodynamical and magnetic instabilities. Eventually, we discuss the role of the dynamo on turbulent transport coefficients and see how our measurements compare to previous theories.