A novel collisionless fluid plasma model based on non-local closure incorporating cyclotron resonance effect

Wave-particle interaction plays an essential role in many space plasma environments, such as solar wind and the earth's magnetosphere. When constructing a model for those systems, we have two choices: kinetic models and fluid models. Fully kinetic simulation models such as the particle-in-cell model require a lot of computational resources and make three-dimensional macroscopic simulations difficult. On the other hand, conventional fluid models such as magnetohydrodynamics (MHD) ignore wave-particle interaction completely. Nevertheless, it is known that wave-particle interaction effect has non-negligible impacts even at macroscopic scales. This motivates us to consider a fluid model that incorporates wave-particle interaction effect. We have developed a non-local closure model that approximates the heat flux tensor components relevant to cyclotron resonance by a linear combination of lower-order moments (number density, fluid velocity, and components of the pressure tensor). This is an extension of the well-known Landau-closure, which considers a non-local closure to the electrostatic component. The resulting dispersion relations of Landau-type closure models give rational function approximations of the plasma dispersion function (Z-function). We show that the proposed closure model can reproduce linear cyclotron damping and temperature anisotropy instabilities, in particular the electromagnetic ion cyclotron (EMIC) instability for which the cyclotron resonance is essential. Basic concepts of the model and simulation result of the EMIC instability will be presented. Although the closure is based on linear kinetic theory, we find the model can reproduce quasilinear relaxation of temperature anisotropy as well. We will also compare our model to the Chew-Goldberger-Low(CGL)-type models, which are another class of collisionless fluid models applicable to low-frequency phenomena. The advantages of each model and its range of application will be discussed.