BASIC MECHANISMS INVOLVED IN THE ADIABATICITY BREAKDOWN OF ELECTRONS TRANSMITTED THROUGH A QUASIPERPENDICULAR SHOCK

Breakdown of adiabaticity of electrons crossing a collisionless shock front is analysed in details. Previous works use to evidence the adiabaticity breakdown in terms of jump of magnetic momentum between upstream and downstream regions. However, such an approach does not provide any information on the physical mechanims responsible for this breakdown within the shock front itself. The purpose of this analysis is to identify these mechanisms within the front with the help of numerical simulations. The shock of concern herein is quasiperpendicular and in supercritical regime. Results are issued from test particles simulations based on the use of all fields components issued from 2-D self consistent full particle simulations and of spherical shell velocity distributions of incoming electrons cubes. Test electrons are launched from the same position upstream from the shock front, so that any difference between will result from their relative phases in the velocity space. Present analysis shows that adiabaticity deviation takes place locally within the first part of the ramp where the gradient of the electrostatic field is positive in good qualitative agreement with theory of [1]. Indeed, this theory predicts that when this positive gradient seen by an electron crossing the shock front is large enough, the electron gyromotion is strongly affected and adiabaticity breakdown may take place [2]. Presently, two appropriate sets of complementary diagnostics respectively based on (i) the individual electro