Almost monoenergetic ions: new support for Alfvén ideas on the role of electric currents in space plasmas?

Abstract

A new kind of energetic particle spectra consisting of 1–3 narrow lines was discovered in the DOK-2 experiments on board of the Interball-1 and 2 spacecrafts during a period from August 1995 to August 1999 in the region upstream of the Earth's bow shock, in the magnetosheath, and near the border of the magnetotail plasma sheet. The relative width at half maximum of these lines was of 15–30%. Ion energy values varied for different events from 30 to 600 keV but were almost unchanged during each event. In two-peak spectra the energy values ratio was 1:2, and in three peak spectra the ratios were 1:2(5–6). Such line spectra cannot be explained by current models of particle acceleration or escape from the magnetosphere. We propose a hypothesis explaining the origin and the main features of these ions by solar wind ions acceleration in a burst of strong electrostatic field (50–100 mV/m) in a small region (1000–5000 km). This burst can be a result of a disruption of a current filament of the magnetopause or the magnetotail current system. By such a disruption the whole potential difference over the magnetosphere due to convective electric field develops over a small region accelerating plasma ions to energies ∼100 keV. If this mechanism is really working it may give a new support to Alfvén ideas on the dualism and the role of electric currents in space plasmas.