The effect of the geomagnetic field on negative voltage spheres in the ionospheric plasma: fluid simulation

Abstract

Abstract Experiments involving the interaction of spherical conducting objects biased with high voltages in the Low-Barth-Orbit (LEO) environment have been conducted and designed. In these experiments, both positive and negative voltages have been applied to the spheres, Previously, there have been theoretical and numerical studies of positive voltage spheres in plasmas with and without B fields. There also have been studies of negative voltage objects in unmagnetized plasmas. Here, we used a fluid Model to study the plasma response to a negative voltage sphere immersed in a magnetized plasma. Our main purpose was to investigate the rote of the B field during the early-time interaction between the negative voltage sphere and the ambient plasma in the LEO environment. In this study, different applied voltages, B field strengths, and risetimes of the applied voltages were considered. It was found that with the strength of the geomagnetic field the ions are basically not affected by the B field on the time scale of hundreds of plasma periods considered in this study. The ion density distribution around the sphere and the collected ion flux by the sphere are basically the same as in the case without the B field. The electron motion is strongly affected by the B field. One effect is to change the nature of the electron overshoot oscillation from regular to somewhat turbulent. Although the electrons move along the B field much more easily than across the B field, some redirection effect causes the electron density to distribute as if the B field effect is minimal. The sheath structure and the electric field around the sphere tend to be spherical. A finite rise-time of the applied voltage reduces the oscillatory activities and delays the ion acceleration. However, the effect of the rise-time depands on both the duration of the rise-time and the ion plasma period.