Speaker
Description
Space plasma simulations are typically categorized into fluid and kinetic models, which are employed for modeling macroscopic and microscopic phenomena, respectively. Fluid models consider only lower-order moments (usually up to the second order), whereas kinetic models have degrees of freedom that are more than one order of magnitude larger. This introduces a significant gap between the two different approaches both in terms of physics and computational requirement, making it difficult to investigate the coupling between different scales. To bridge this gap, we propose a novel kinetic closure that incorpolates the cyclotron resonance effect into a fluid model. It adopts the same strategy as the Hammett-Perkins closure for Landau damping but applies it to electromagnetic flucuations for a fluid species with a pressure tensor that includes off-diagonal components. Although the model is based on linear theory, nonlinear simulations of temperature anisotropy instabilities demonstrate that it is capable of describing quasi-linear isotropization and saturation in the nonlinear phase. We show that inclusion of the off-diagonal components of the pressure tensor is crucial for reproducing qualitatively correct nonlinear behavior. The proposed approach may be an important step toward an intermediate model between fluid and kinetic models.
