Magnetic reconnection as a driver for a sub-ion scale cascade in plasma turbulence: high-resolution 2D and 3D hybrid simulations

We present an alternative path for the generation of a sub-ion scale cascade in collisionless plasma turbulence, triggered by magnetic reconnection. By means of high-resolution two-dimensional and three-dimensional hybrid-kinetic simulations, we provide clear numerical evidences that the development of power-law energy spectra below the so-called ion break occurs as soon as the first magnetic reconnection events take place, regardless of the actual state of the turbulent cascade at magnetohydrodynamic scales. The reconnection-mediated small-scale energy spectra of parallel magnetic fluctuations and density fluctuations exhibit a very stable spectral slope of -2.8, whether or not a large-scale turbulent cascade has already fully developed. Once a quasi-stationary turbulent state is achieved, the spectrum of the total magnetic fluctuations settles towards a spectral index of -5/3 in the MHD range and of -3 at sub-ion scales. Based on our analysis, we suggest that fast energy injection at sub-ion scales via magnetic reconnection may represent a relevant non-local transfer mechanism, simultaneously at play in addition to the "classical" local turbulent energy transfer. Our results are discussed in the context of current theoretical models, numerical simulations employing different approaches and with particular focus on a qualitative and quantitative comparison with solar wind and magnetosheath observations.