Kelvin-Helmholtz Instabilities for Incompressible, Laser, and Magnetospheric Applications

Abstract A series of simulations of the development of Kelvin-Helmholtz instabilities (KHI) between two magnetized (or not) fluids with a common shear layer will be presented. The objective, almost impossible, is to connect between extremely different regimes. One regime is the incompressible regime or weakly compressible regime, described either by the Boussinesq approximation or by the variable density approximation. The other is a regime of compressible dense matter at supersonic speed encountered in laser experiments. The latter is still supersonic but within a low density, encountered at the Earth’s magnetic field external boundary, on the day side, where fast solar winds shock with Earth’s magnetospheric plasma. All regimes will be illustrated and discussed with state-of-the art simulations and/or experiments. In the case of the Earth’s magnetosphere, a digression will be made on the analysis of 3D global MHD simulations of the fine scale turbulent-like velocity structures of the plasma evolving in the plasma sheet. Field and velocity distributions as well as their auto-correlation will be presented with the goal of identifying bulk bubble flows (BBFs). Various numerical and physical effects will be considered, including the effects of the magnetic field for damping KHI, the importance of density gradients, velocity shear, initial perturbation profiles (mono or multi modes), etc., with the goal of addressing all regimes. The extraction of KHI growth rates from simulations will be discussed, with generation of a universal diagram of the instability growth rate as a function of the magnetic field intensity. One goal is the quantification of how nonlinear effects and/or multi-mode instabilities can affect the growth rate and how it differs from the linear regime.

Bio Dr. Jean-Francois Ripoll (Ph.D in 2001, HDR in 2014) is currently expert senior scientist at CEA (Commissariat à l’Energie Atomique) in the Physics Division of the CEA/DIF center close to Paris. He has an adjunct position at the LRC-MESO of Ecole Normale Supérieure de Cachan and is a member of the LMCE (Laboratory of Matter in Extreme Conditions), an institute of University Paris-Saclay (UPS) and CEA. During his past international career, he had the opportunity to work 5 years, from 2002 to 2007 in the United States, working successively at the Center for Turbulence Research at Stanford University for 3 years (2002-2005) and at the Los Alamos National Laboratory (2005-2007). He is actively involved in atmospheric and magnetospheric physics, in particular the modeling of wave-particle interactions and their effects on the dynamics of trapped energetic electrons in the Earth’s inner magnetosphere for space science applications related to space weather, defense, and non-proliferation. He is leading various international research projects that use satellite observations and massively parallel simulations to produce impactful analysis with the best experts of atmospheric and space sciences. Among them, he works actively with LANL colleagues on space physics research studies, through an officially recorded research program with NNSA. He also collaborates with APL/Center for Geospace Storms to simulate active geomagnetic storms and substorms, particle injections, and plasma instability developments in the magnetosphere. He currently leads an ISSI international research group of ~20 scientists on trapped particles in the inner magnetosphere.