Self-similarity and growth of non-linear magnetic Rayleigh-Taylor instability -- Role of the magnetic field strength

Abstract: The non-linear regime of the magnetic Rayleigh-Taylor instability (MRTI) plays a crucial role in the transportation and mixing of material in a wide range of laboratory to astrophysical systems. But several fundamental aspects of this regime remain poorly understood. Previous MRTI studies assumed MRTI to have a self-similar, quadratic growth in the non-linear regime, similar to the hydrodynamic (HD) RTI. However, neither the self-similarity nor the relevance of the HD scaling for the MRTI has been proved analytically. Further, the role of magnetic field on the evolution of the instability remain unexplored. Towards this, we perform analytical and numerical study of the MRTI with uniform magnetic field. Our study reveals that the imposed magnetic field deviates the MRTI evolution from self-similarity. However, the HD RTI scaling becomes relevant to the MRTI evolution when the non-linear dynamics dominate the imposed magnetic field. A formula for the $\alpha_{mhd}$, a quantity which represents the non-linear growth of instability in the self-similar regime, was obtained. The formula of $\alpha_{mhd}$ highlight the physical processes that could dictate the growth of instability. Numerical simulations of the MRTI showed the quantitative variation of these physical processes and $\alpha_{mhd}$ across a wide range of magnetic field strengths. Thus, the current study proves, analytically and numerically, the role of magnetic fields on the evolution of MRTI and the factors that influence of non-linear growth constant of the instability.