Growth or decay - decaying magnetohydrodynamics meets the turbulent dynamo

The saturation of the turbulent dynamo remains a highly important, outstanding problem for all small-scale dynamo theories. Beattie, et al. (2023a) showed numerically that the saturation is completely independent of the initial magnetic field conditions, even if the magnetic field decays into the saturation, which may be present in the post-shock region of supernova remnants. The decaying magnetic field presents a novel way of understanding dynamo saturation where the mechanisms for saturation are amplified due to the strong field. Preliminary analysis shows that the decaying field finds a force-free equilibrium state and that the decay is faster than Ohmic, potentially due to reconnection. In this project we will do a detailed analysis of the decay and force-free magnetic field in high-resolution 3D simulations of decaying plasma that are being constantly injected with momentum to stir weak turbulent modes. This will provide deep insights into the nature of dynamo saturation, and the stability of force-free magnetic fields, which are important for magnetisation in the early Universe and magnetic fields around compact objects.