Acceleration region dynamics in a magnetically shielded Hall thruster

The influence of the cathode flow fraction and facility background pressure on the acceleration region of a magnetically shielded Hall thruster is experimentally characterized. The location of the acceleration region is measured using laser-induced fluorescence on H9, a 9-kW class Hall thruster, for six different facility background pressures and four different cathode flow fractions. The results show that when the facility pressure is increased from 7.1 × 10– 6 to 3.0 × 10– 5 Torr-Xe, the acceleration region shifts inward 1.6 ± 0.5 mm. Similarly, when the cathode flow fraction is increased from 7% to 15%, the acceleration region shifts inward 0.9 ± 0.5 mm. This experiment leads to two conclusions. First, introducing neutrals in the cathode region can directly impact the acceleration mechanism in the thruster. Second, changing the cathode flow fraction affects the acceleration region of the thruster in a similar manner as the background pressure. This result is discussed in the context of the neutral density environment created by both injection schemes. Calculations of this parameter show that the increase in neutral density in the proximity of the acceleration region is similar when varying the background pressure and changing the cathode flow fraction. This provides correlational evidence linking the role of neutral density to the acceleration region shift.