stockholmuniversity.zoom.us/j/940229961
Magnetohydrodynamic dynamo effects are at the core of magnetic-field amplification in many astrophysical systems ranging from planets to galaxy clusters. In particular, the origin, self-organisation and sustenance of magnetic fields observed on scales comparable to the global time and spatial scales of such systems remains one of the most fascinating natural phenomena in the Universe, but is also one of the most challenging to understand. Indeed, despite much experimental, theoretical and numerical progress over the last fifty years, a firm basis for large-scale dynamo theory rooted in first principles is still lacking due to the fundamentally non-perturbative nature of the problem. Absent some new, game-changing mathematics to circumvent this issue, numerical exploration of regimes as close to asymptotic as possible to planetary and astrophysical regimes currently remains the most promising avenue of research for further progress at the fundamental level. In this talk I will present a few recent numerical results on helical large-scale dynamos attempting to make a modest move in this direction, using a simple setup aimed at optimizing the conditions to reach an asymptotic regime. I will notably argue that the notorious catastrophic alpha-quenching problem of large-scale helical dynamos may be partly mitigated in systems with an inhomogeneous (sinusoidal) distribution of helicity, such as encountered in rotating astrophysical bodies. I will also briefly touch on some important but non-trivial questions that these results raise, including the relative kinetic and magnetic Reynolds number dependence of such inhomogeneous large-scale dynamos, the possible effects of fast magnetic reconnection on saturated dynamos at large magnetic Reynolds numbers, and whether pushing for HPC simulations at ever larger resolutions is the reasonable thing to keep doing in the current climate emergency.