We consider the use of “extended fluid models” as a viable alternative to computationally demanding kinetic simulations in order to manage the global large scale evolution of a collisionless plasma while accounting for the main effects that come into play when spatial micro-scales of the order of the ion inertial scale di and of the thermal ion Larmor radius .i are formed. We present an extended two-fluid model that retains finite Larmor radius (FLR) corrections to the ion pressure tensor while electron inertia terms and heat fluxes are neglected. Within this model we calculate analytic FLR plasma equilibria in the presence of a shear flow and elucidate the role of the magnetic field asymmetry. Using a Hybrid Vlasov code, we show that these analytic equilibria offer a significant improvement with respect to conventional magnetohydrodynamic shear-flow equilibria when initializing kinetic simulation

Non-Maxwellian metaequilibria can exist in low-collisionality plasmas as evidenced by satellite and laboratory measurements. By including the full pressure tensor dynamics in a fluid plasma model, we show that a sheared velocity field can provide an effective mechanism that makes an initial isotropic state anisotropic and agyrotropic. We discuss how the propagation of magnetoelastic waves can affect the pressure tensor anisotropization and its spatial filamentation which are due to the action of both the magnetic field and flow strain tensor. We support this analysis by a numerical integration of the nonlinear equations describing the pressure tensor evolution.The aim of this Letter is to show that a sheared velocity field in a weakly collisional, magnetized plasma drives a macroscopic pressure anisotropization in the plane of the velocity strain tensor. This represents a general mechanism when collisional relaxation is absent or slow that causes part of the kinetic energy of the plasma flow to be locally transformed into anisotropic "internal energy". This energy conversion implies that shear flows do not affect the plasma dynamics only through the fluid destabilization of Kelvin-Helmholtz (KH) modes [1] or by breaking the correlation length of unstable modes [2,3] responsible e.g., for anomalous energy transport in magnetically confined plasmas, but can lead to the onset of additional phase space instabilities driven by the induced pressure anisotropy.In magnetized plasmas the fast particle gyromotion in a sufficiently strong field makes the pressure tensor isotropic in the plane perpendicular to the magnetic field direction but allows for different parallel and perpendicular pressures (gyrotropic pressure as is the case for the double-adiabatic or CGL[4] closure). On the contrary, the fluid strain Σ ij ≡ ∂u i /∂x j in the sheared fluid velocity u i (x) has a twofold effect: first, through its rotational component it combines or competes with the gyrotropic effect due to the magnetic field, second it induces pressure anisotropy (agyrotropic pressure) in the plane perpendicular to the magnetic field (taken to coincide with the velocity shear plane) through its incompressible rate of shear (its symmetrical traceless component).Here we discuss the role of the flow strain in the dynamic equations of the full pressure tensor as obtained from the second moment of Vlasov Equation (VE), thus going beyond both the CGL closure and the Finite Larmor Radius (FLR) corrections[5] approach. We focus in particular on the dynamics of the full pressure tensor within a 1-fluid description of a dissipationless magnetized plasma and show how the propagation of "magnetoelastic" waves can affect the pressure anisotropization and small spatial scale formation due to the interplay * daniele.del-sarto@univ-lorraine.fr between the gyrotropic and the non-gyrotropic dynamics induced by the magnetic field and by the strain tensor.Non-Maxwellian states, sometimes exhibiting pressure agyrotropy [6][7][8], are observed both experimentally [6]...