Spatial Characterization of Oxygen Negative Ions in Afterglow of an Inductively Coupled Plasma

Abstract

Spatial profile of oxygen negative ions produced during the afterglow phase of an inductively coupled radiofrequency (RF) plasma is experimentally investigated, motivated by the development of a gridded ion thruster incorporating both positive and negative ion sources. It is found that the negative ion density exhibits a peak approximately 40–100 mm downstream of the inductive plasma source, depending on the working gas pressure. It is presented that the axial profile of the negative ions in the afterglow mimics the plasma density profile observed during the RF-ON phase, in which the peak of the positive ion density is formed downstream of the source exit as a result of charge exchange collisions of spontaneously accelerated positive ions.