Experimental Simulation of Spacecraft Charging by Artificial Ion Beam Emission

Charging of a small electrically floated body, equipped with an unneutralized microwave ion source, was experimentally studied in a vacuum chamber. When a xenon ion beam of 16 mm in diameter was released from a cubic floating body, 10 cm on each side, the body was negatively charged at a rate of I_b/C, where I_b is the ion-beam current and C is the capacitance between the floated body and the ground. For large I_b/C parameters, the body potential changes faster than the xenon ions can react. This simulation results in space-charge-induced potential oscillations, which are detected in experimental measurements and observed in numerical simulations. The time scale of the oscillation relaxation time was found to be at least several times, corresponding to the ion movements around the body. As expected, the steady-state potential of the floated body was relatively negative to the vacuum-facility ground at a value equal to the magnitude of the ion-beam voltage