Plume study of a 1.35-kW SPT-100 using an ExB probe

The ion energy distributions of Xe1+, Xe2+, and Xe3+ ions in the SPT-100 plume obtained 50 cm and 1 m from the thruster exit with an ExB probe are presented. Most of the ion species distribution functions exhibit features associated with both Maxwellian and Druyvesteyn distributions. Therefore, the nature of the ion energy distribution in the SPT-100 plume is established by the competing effects of ion acceleration in the discharge chamber and collisional processes beyond the ion production zone. Comparison of beam energy and ion energy spread 50 cm and I m from the thruster exit reveal that the energy distribution of the far-field plume ions varies little as the ions move away from the thruster. The angular profiles of the ion species fractions and the beam energy data suggest that, whereas Xe2+ and Xe3+ ions are produced near the thruster exit, Xe1+ ions are created farther upstream in the discharge chamber.