Experimental study on low-frequency oscillation of the plume divergence angle of hall thrusters

The plume divergence angle of Hall thrusters refers to its discharge plasma in space beam angle plume expansion. The plume is high-speed and thin plasma and less divergence. These high-speed ions will do harm to the normal run of spacecraft, thus the evaluations and measurements of divergence angle is one of the important contents in Hall thruster research. Though a Hall thruster is operated with DC discharge, many physical processes can lead to the discharge current oscillation, such as the collisions between particles in the discharge channel and so on. Previous experiments show that the low-frequency oscillation of Hall thrusters will cause the plume divergence angle increase, thereby increasing the plume of pollution. However, it is very difficult to obtain the dynamic characteristics of the plume divergence angle in the low-frequency oscillation time scale through traditional methods. In this paper, the low-frequency oscillating current and ion current at each measurement point along radial directions are recorded, all of which corresponding to the same low-frequency oscillation current. Through using the discharge current low frequency oscillation as the modulation signal, the ion current density distribution along the radial directions can be obtained through the data fitting. Then the plume divergence angle in different times during low-frequency oscillations scales can be calculated. The measurement principle diagram is shown in Figure (1). This method can measure the plume divergence angle in a short period of time, which avoids the use of the high-speed mobile devices, and then a further physical mechanism discussion of the plume divergence low-frequency oscillations is given according to the measurement results and theoretical analysis.