Because of the anticipated use of high-voltage power sources on future space platforms, there is an increased interest in elucidating the phenomena associated with the interactions of a high-voltage conductor and the ionospheric plasma at low-Earth-orbit altitudes. Currently there are ongoing rocket, laboratory and modelling programs, and an electrodynamic tether will be flown on the Space Shuttle. All of these programs involve the current collection characteristics of high-voltage spheres embedded in both magnetized and nonmagnetized thermal plasmas. In support of these efforts, the authors have solved the time-dependent nonlinear fluid equations for ions and electrons and the Poisson equation in order to study the response of a nonmagnetized plasma to 'negative' high-voltage spheres. Simulations were conducted for a range of voltages (-10 to -10000 V) and for plasma densities from 104to 106cm-3. The temporal evolution of the plasma was followed all the way to the steady state. In all simulations, there were certain qualitative similarities in the plasma response.
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