Ion resonance acceleration by dipolarization fronts: analytic theory and spacecraft observation

International audienceIn this paper, we consider the mechanism of ion acceleration by dipolarization fronts in the Earth's mag-netotail. The statistics of dipolarization front observations by Interball-tail have been collected from 1995 to 1998 (51 events). We demonstrate that near dipolarization fronts bursts of energetic ions are often observed with an average energy of about 100–200 keV. We develop the analytical model of the ion resonance interaction with dipolariza-tion fronts to describe the observed acceleration. We compare the model and the observations to estimate the width of fronts along the dawn-dusk direction, R y. The mean value is R y ∼ 6 R E

Charged particle acceleration by intermittent electromagnetic turbulence

International audienceWe studied the role of intermittency in the process of acceleration and transport of charged particles by electromagnetic turbulence. We propose a simple model of electromagnetic turbulence with a variable level of intermittency. The magnetic field is described as a superposition of an ensemble of magnetostatic plane waves and of spatially localized dynamic magnetic clouds. The amplitudes of magnetic clouds are distributed according to an intermittent map. The model approximates essential properties of turbulence observed 'in situ' in the neutral plane of the Earth's magnetotail. Numerical integration of charged particle trajectories in such a dynamic electromagnetic environment shows that, for the fixed time interval, the higher the level of intermittency, the higher the energy gain. Moreover, in a sufficiently intermittent turbulence, particle acceleration occurs without significant intensification of the spatial transport

Asymmetric thin current sheets in the Earth's magnetotail.

In a frame of self-consistent model of thin current sheets (TCSs), where the tension of magnetic field lines is balanced by the inertial force of ion motion, we investigated the influence of the asymmetry of plasma sources on the structure and spatial localization of the equilibrium solution. For simplicity only one ion source is considered. It is shown that the asymmetry of plasma sources does not modify dramatically the bulk of the current carried by ions at meandering orbits. Negative diamagnetic currents are significantly stronger at the side of a plasma source due to enhanced plasma density in this region. The center of TCS is displaced to the opposite side of the plasma source to keep the pressure balance. One could speculate that this phenomenon might be a cause of flapping motions of the TCS due to the natural variability of plasma sources