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We investigate the acceleration and transport of planetary ions within Kelvin-Helmholtz (KH) vortices that develop in the magnetospheric flanks of Mercury, using single-particle trajectory calculations in a field model obtained from MHD simulations. Due to the presence of heavy ions of planetary origin (e.g., O+, Na+, and K+) following ionization of exospheric neutrals and the complicated field structure during the KH vortex development, the scale of electric field variation may be comparable with ion gyration motion. Therefore ions may experience non-adiabatic energization as they drift across the magnetopause. In this study, we consider realistic configurations for both dawn and dusk magnetospheric flanks, and we focus on the effect of the spatial and temporal variations of the electric field magnitude and orientation along the ion path on the ion dynamics. We show that the intensification rather than the change of orientation is responsible for large non-adiabatic energization of heavy ions of planetary origin. This energization systematically occurs for ions with low initial energies in the direction perpendicular to the magnetic field, the energy gain being of the order of the energy corresponding to the maximum ExB drift speed, ɛmax, in a like manner to a pickup ion process. It is also found that ions that have initial energies comparable to ɛmax may be decelerated depending upon gyration phase. We find that ions with initial perpendicular energies much larger than ɛmax are little affected along the ion path through KH vortices. By comparing dynamical regimesin the dawn versus dusk regions, and also by considering different IMF directions, we show that the ion transport across the magnetopause is controlled by the orientation of the magnetosheath electric field and that the rate of energization depends upon the scale of KH vortices versus Larmor radii.

International audience; Because of a large velocity shear in the flanks of Mercury's magnetosphere, Kelvin-Helmholtz (KH) instability is expected to develop and to play a role in mass and momentum transport across the magnetopause. Using single particle simulations in field configurations obtained from MHD simulations, we investigate the dynamics of ions in this region. We focus on heavy ions of planetary origin (e.g., Na , K , Mg ) that may be found on either side of the magnetopause, due to the ionization of exospheric neutrals. Because characteristic spatial and temporal scales of KH instability at Mercury are comparable to or smaller than typical ion scales, we show that under such conditions the guiding center approximation is invalid and that planetary ions may be transported in a non-adiabatic (magnetic moment violation) manner. In this study, we focus on the effect of the electric field that develops within KH vortices. We show that the intensification rather than the change of orientation of this electric field is responsible for large (up to hundreds of eVs or a few keVs) energization of heavy planetary ions. This energization occurs systematically for particles with low initial energies in the perpendicular direction, the energy realized being of the order of the energy corresponding to the maximum ExB drift speed, εmax, in a like manner to a pickup ion process. It is also found that particles that have initial energies comparable to εmax may be decelerated depending upon gyration phase. Finally, we find that particles with initial perpendicular energies much larger than εmax are little affected during transport through KH vortices. We suggest that the development of KH instabilities in Mercury's magnetospheric flanks may lead to significant ion energization and pitch angle diffusion, and may thus play a prominent role in plasma mixing at the magnetopause.

Through analysis of variable temperature neutron powder diffraction data, we present solutions for the magnetic structures of SrMn7O12, CdMn7O12, and PbMn7O12 in all long-range ordered phases. The three compounds were found to have magnetic structures analogous to that reported for CaMn7O12. They all feature a higher temperature lock-in phase with commensurate magneto-orbital coupling, and a delocked, multi-k magnetic ground state where incommensurate magneto-orbital coupling gives rise to a constant-moment magnetic helix with modulated spin helicity. CdMn7O12 represents a special case in which the orbital modulation is commensurate with the crystal lattice and involves stacking of fully and partially polarized orbital states. Our results provide a robust confirmation of the phenomenological model for magneto-orbital coupling previously presented for CaMn7O12. Furthermore, we show that the model is universal to the A quadruple perovskite manganites synthesised to date, and that it is tunable by selection of the A-site ionic radius.

International audience; We investigate the growth of the mixing layer thickness in the Kelvin-Helmholtz instability (KHI) using an extended-local MHD model to estimate the ion loss rate from the Martian ionopause. The KHI is expected to play a major role in transporting mass, momentum and energy across the ionopause between the sheath flow and ionospheric plasmas. Since the mixing layer has a finite thickness between them, this layer has a potential for the removal of a huge amount of ions from Mars through its history. The recent MAVEN observation reported that the density ratio across the ionopause reaches as high as 100 5000. With such a large density ratio, compressible effects are expected to modify the structure of the KH vortices and the evolution of the mixing layer by generating high-amplitude nonlinear fast-mode plane waves from ridges of the KH waves. In order to reproduce Martian ionopause, we developed an extended-local MHD model with aperiodic boundary condition for the evaluation of traveling waves along the dayside Martian ionopause ( 6,000km). Spatial resolution is set with 3km to resolve the thin mixing layer. We find two factors that accelerate the growth of the mixing layer. Firstly, the KH wave with the fastest growing mode behaves like a wall to the leading vortex in the aperiodic condition. The sheath flow is stagnated by this wall-like structure and induces an enhanced vortex return flow, resulting in a deeper excavation of the ionospheric plasma. Secondly, fast-mode rarefaction waves generated by compressible effects make wall-like structures more effective by lowering pressure around antinodes of the KH waves. Such a pressure profile further accelerates the stagnation and the excavation. In addition, KH vortices are merging not one by one but also some vortices are merged together at time. Thus, the large wave like structure can be seen when the effect of compressibility is not so large. The mixing layer spread with the lapse of time and it depends on the density ratio, its relation can be described the function of the logarithm. Furthermore, we estimate the ion loss rate from our results and it agrees with the MAVEN observational results.