Drift mirror instability revisited, 1, Cold electron temperature limit

Abstract

Abstract. Linear theory of the drift-mirror instability in high-/• plasma is reconsidered referring to basic principles for the two cases of a one-and a twocomponent ion plasma in presence of a cold electron background. In both cases the cold electrons serve to shortcut the parallel electric field component which imposes the condition of vanishing the field-aligned current. The corresponding low-frequency dispersion relation is derived in the fluid approximation as well as from kinetic theory including nonvanishing gradients in the density. The free energy of the unstable mode is taken from two sources: the pressure anisotropy and the spatial inhomogeneity of the plasma. The dispersion relation contains a correction which originates from the inclusion of the bending of the magnetic field that is caused by the reaction of the field to the total pressure force. It is shown that the mirror force substantially reduces the phase velocity which is in favour of instability since this requires phase velocities less than the drift speed. The direction of phase velocity becomes antiparallel to that of the pure density-gradient drift velocity. Even for a. mirror-stable plasma an instability arises which is solely due to inhomogeneity. We ana, lyze the transition to the classical mirror instability.Application to ring current (hot ring current ions plus cold plasmasphere ions) and magnetosheath (hot sheath ions only) conditions is presented and is in agreement with observational indication of the apparent stability of the pure mirror mode in the ring current. comets, and in the solar wind. In the high-/3 plasma of the solar wind and the magnetosheath, mirror modes

Propagation pattern of low frequency waves in the terrestrial magnetosheath

“…In the case of the magnetosheath the mirror mode waves are often observed, and the existence of www.ann-geophys.net/24/2441/2006/the drift mirror mode has been expected. The drift mirror mode, however, propagates perpendicular to the density gradient direction (Hasegawa, 1969;Pokhotelov et al, 2001), whereas our results prefer the parallel direction. Perhaps the drift mirror mode is operating in the magnetosheath, but the frequency is proportional to logarithm of the density distribution, ω∝∇ log n, and therefore the wave drift effect would be too small to detect.…”

Occurrence rate of magnetic holes between 0.72 and 1 AU: comparative study of Cluster and VEX data

“…1 is very similar to mirror wave structures observed in the magnetosheath (Balikhin et al, 2003Chisham et al, 1999). Comprehensive theory of mirror instability that accounts for electron temperature (Pokhotelov et al, 2000), finite Larmor radius effects (Pokhotelov et al, 2004), plasma gradients (Pokhotelov et al, 2001), non-Maxwellian and multicomponent plasmas (Pokhotelov et al, 2008) has been developed. Analytical studies of the quasilinear and nonlinear stages of the instability demonstrated how the mirror waves can be carried by the solar wind over long distances through the mirror stable plasma.…”

Drift mirror instability in space plasmas, 2, Nonzero electron temperature effects

“…For our study we limit consideration of perturbations of the equilibrium state having frequencies smaller than the ion cyclotron frequency wci. According to Pokhotelov et al [2001], the drift mirror mode is described by the perpendicular pressure balance condi- All perturbed values in (1) are assumed to vary both in time and space as exp(-iwt + ik. r), /•0 is the permeability of free space, w is the wave frequency, and kll are the components of the wave vector k perpendicular and parallel to the external magnetic field, fi-k,II -2•op-k,11/B2 is the ratio of perpendicular (parallel) plasma pressure to magnetic field pressure, P-k,II are perpendicular and parallel scalar pressure components, 5p_k is the variation of the perpendicular plasma pressure and 5Bii is the compressional perturbation of the magnetic field.…”

“…Hence the given paper can be considered as an extension of our previous approach to the drift mirror instability [Pokhotelov et al, 2001], which was limited by the cold electron temperature limit, that is to the case, when Te • 0.…”