ИСТИНА

Beginning from the 1970th, spacecraft observations in the Earth’s auroral region have revealed many interesting characteristics of plasma and field interactions. The most intriguing of them are the frequently observed conic-shape velocity distributions of both protons and electrons at the low auroral latitudes. Theoretical considerations for the explaining of these characteristic distributions are supposed to be (i) particle acceleration by the electrostatic of induction electric fields in the presence of strong spatial gradients or (ii) particle acceleration by the wave-particle interaction. Meanwhile, these suggestions are rather contradictory and do not generally explain physical processes behind formation of the distributions of this kind, which remain unclear till now. Recently, the forward- and reverse conic proton and electron distributions have been registered at the low latitudes of the polar magnetosphere of Jupiter. In our work, we propose a simple model of formation of conic plasma distribution in the auroral region, when plasma particles are initially pre-thermalized and later their flows propagate along a flux tube. In a course of the almost adiabatic motion, the integrals of particle motion are conserved. Particle acceleration processes during particle motion in magnetic tubes are supposed to be generally weak and have not been taken into account before. In a frame of the proposed model, it is shown that plasma distributions should acquire the conic shape due to a transformation of their thermal energy of motion into the energy of the particle flow along the magnetic field lines by the mirror forces. A particle escape into the loss cone is not necessary for the formation of such a distribution. This mechanism can be realized in magnetic flux tubes of different localizations in space plasma, particularly, in planetary magnetospheres. Results are discussed and compared with the available theoretical models and in situ observations. This work was supported by the Russian Science Foundation Grant 23-12-00031