Experimental Visualization of Ion Thruster Neutralization Phenomena

Understanding of neutralization phenomena is important to develop ion thrusters with higher efficiency and durability. A 2-D ion thruster with a miniature microwave neutralizer was visualized in this paper to investigate neutralization phenomena. The thruster can emit bright sheet-shaped ion beams. The neutralizer current can be controlled by the supplied microwave power. Observation of the downstream region and measurements of the currents and potential confirmed that insufficient neutralizer current increased the ion beamwidth, space potential increase in the downstream region, and semicircular luminescence zone formation in the region. These phenomena imply the 2-D formation of a virtual anode in the downstream region of the grid system, and indicate that 2-D or 3-D evaluations are necessary to elucidate neutralization phenomena.