Magnetic field configuration effects on a miniature DC ion thruster with an inverted potential structure

To improve the mass utilization and total efficiency of miniature direct current (DC) ion thrusters, this article proposes a graphene–oxide–semiconductor (GOS) electron source as a cathode in the discharge chamber and neutralizer. To apply the GOS device to the discharge chamber, multiple electron sources were positioned downstream to provide sufficient electrons for plasma generation. Accordingly, the anode was placed upstream of the discharge chamber; thus, the potential structure was inverted from that of a conventional device. Based on this concept, two discharge chamber types were developed with different magnetic field configurations (1- and 2-Cusp types) using a filament cathode and their performance was experimentally evaluated. Probe diagnostics results showed that plasma was generated mainly in the center of the discharge chamber in 1-Cusp, whereas it was generated in the entire discharge chamber in 2-Cusp. Regarding ion beam extraction with 211-hole grids, 1-Cusp exhibited a higher screen current than 2-Cusp. However, using 391-hole grids with an expanded ion-extraction region, 2-Cusp outperformed 1-Cusp with 211-hole grids, attaining a minimum discharge loss of 273 W/A (excluding filament power) and a maximum mass utilization efficiency of 0.48.