Turbulence and kinetic processes in magnetized space plasmas have been extensively investigated over the past decades via in-situ spacecraft measurements, theoretical models and numerical simulations. In particular, multi-point high-resolution measurements from the Cluster and MMS space missions brought to light an entire new world of processes, taking place at the plasma kinetic scales, and exposed new challenges for their theoretical interpretation. A long-lasting debate concerns the nature of ion and electron scale fluctuations in solar-wind turbulence and their dissipation via collisionless plasma mechanisms. Alongside observations, numerical simulations have always played a central role in providing a test ground for existing theories and models. In this Perspective, we discuss the advances achieved with our 3D3V (reduced and fully) kinetic simulations, as well as the main questions left open (or raised) by these studies. To this end, we combine data from our recent kinetic simulations of both freely decaying and continuously driven fluctuations to assess the similarities and/or differences in the properties of plasma turbulence in the sub-ion range. Finally, we discuss possible future directions in the field and highlight the need to combine different types of numerical and observational approaches to improve the understanding of turbulent space plasmas.
Bibliographical noteKAUST Repository Item: Exported on 2022-06-14
Acknowledgements: SC and DG acknowledge the generous hospitality of the Wolfgang Pauli Institute in Vienna, where the first discussions leading to this work took place. We acknowledge PRACE for awarding us access to Marconi at CINECA, Italy, where the calculations with the HVM code were performed under the grant No. 2017174107. The Cray XC40, Shaheen, at the King Abdullah University of Science and Technology (KAUST) in Thuwal, Saudi Arabia was utilized for the simulation performed with the OSIRIS code. LF acknowledges PRACE for awarding him access to Cartesius at SURFsara, the Netherlands, through the DECI-13 (Distributed European Computing Initiative) call (project HybTurb3D) where the HPIC simulation was performed, and INAF and CINECA for awarding him access to Marconi within the framework of the MoU New Frontiers in Astrophysics: HPC and New Generation Data Exploration (project INA17_C4A26), where new further analysis of the HPIC data has been performed. The authors would like to acknowledge the OSIRIS Consortium, consisting of UCLA and IST (Lisbon, Portugal) for the use of OSIRIS 3.0 and for providing access to the OSIRIS 3.0 framework. SC acknowledges Dr. C. Cavazzoni and Dr. M. Guarrasi (CINECA, Italy) for their contributions to HVM code parallelization, performance and implementation on Marconi-KNL. The authors also acknowledge useful discussions with Alfred Mallet, Lev Arzamasskiy, Bill Dorland, Matt Kunz, Simone Landi, Emanuele Papini, Frank Jenko, and David Burgess. Funding. SC was supported by the National Aeronautics and Space Administration under Grant No. NNX16AK09G issued through the Heliophysics Supporting Research Program. LF was supported by the UK Science and Technology Facilities Council (STFC) grant ST/P000622/1.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.