Hall magnetohydrodynamics in a strong magnetic field

For a plasma embedded in a strong external magnetic field, the spatial structures tend to develop fine scales preferentially across the field, rather than along the parallel direction. This feature, which allowed a major simplification in the theoretical structure of one-fluid magnetohydrodynamics (leading to reduced magnetohydrodynamics), is exploited here to derive what may be called the reduced Hall magnetohydrodynamic equations (RHMHD) reflecting two-fluid effects such as the Hall current and the electron pressure. These physical effects, which can be relevant in astrophysical environments and also in fusion plasmas, allow for the propagation of circularly polarized normal modes such as whistlers and shear/ion-cyclotron waves. In this paper, the RHMHD system of equations is integrated numerically, to investigate externally driven turbulence.