Application of hall thrusters with modulated oscillations

Hall thrusters contain many instabilities which are known to affect thruster performance, with instability strength varying with thruster regime. One such instability, the breathing mode, can dominate the discharge with current oscillation amplitudes equal to the mean current value. Previous works have shown these large amplitude oscillations can be induced by relatively small oscillations in the discharge voltage by resonating with the natural instability around 10-30 kHz. Theoretical works have also shown that thrust of an oscillating plasma thruster can be throttled and increased if ion energy oscillates with the current. Thrust increases when ion energy oscillations are large and in phase with ion current, while thrust decreases when the two are out of phase. A method was developed to measure time-dependent energy of the ions using a retarding potential analyzer. Measurements of the thruster plume demonstrate the required ion energy oscillations in a Cylindrical Hall thruster. These measurements taken with separate measurements of ion energy provide the ion phase angle, and it is shown that the phase can be controlled by slightly altering the frequency of modulations in the thruster.