PARTICLE SIMULATIONS OF IONOSPHERIC INJECTION EXPERIMENTS - COMPARISON WITH CRIT-II

A one-dimensional particle-in-cell code has been used to study the bar ium release experiment CRIT II. The electrodynamic response of the ion osphere to these injections has been modeled by magnetic-field-aligned currents, using the concept of Alfven conductivity. After the active phase, when the fast part of the neutral barium cloud passed the paylo ad, the particle detector 5AB in the CRIT II experiment, aimed almost perpendicular to the ambient magnetic field B in the direction toward the release, showed two clearly defined types of peaks having differen t durations, frequencies, and energy distributions. This particle ener gy spectrum has been reproduced in the numerical simulations. It is sh own that geometrical effects and phase shifts of the ions are of secon dary importance for the creation of the double-peaked structure. A qua litative model, based on the selective acceleration of barium ions due to electric fields set up by the injection process, is developed to e xplain the observations.