Zhang Chaohai

Experimental study on the role of a resistor in the filter of Hall thrusters

A filter is a mainly component applied to reduce the discharge current low frequency oscillation in the range of 10–100 kHz. The only form of the filter in actual use involves RLC networks, whose design originates from the 1970s, but even now, researchers are unaware of the actual primary motivations for the resistor’s presence [S. Barral et al., AIAA Paper 2008-4632, 2008]. Therefore, the role of the resistor in the filter is experimentally studied and discussed through the analysis of control system and electric circuit theory. Experimental results and analysis indicate that the presence of a resistor makes the filter having the phase compensation function. The proper phase-angle and amplitude provided by the filter would increase or decrease the ion mobility and be helpful to balance the ion production in the discharge channel and then to decrease the fluctuation of the plasma density and lower the low frequency oscillation.

Study on breathing mode oscillation suppression of self-excited Hall thrusters

It is found that the breathing mode oscillation of the discharge current is suppressed notably in a Hall thruster operating with the electromagnets driven in series by the discharge current. In order to study the physical mechanism of this suppression, the ionization distribution is measured experimentally and the spatiotemporal features of the ionization front motion are studied numerically with a one-dimensional quasineutrality hydrodynamic model. Results show that the ionization front motion is restricted in a small range due to the closed-loop feedback control of the magnetic field. The steady-state ionization distribution is narrow and condensed when the electromagnetic coils connect in series with the discharge circuit. The different magnetic field excitation accompanied by different ionization characteristics is the main reason for the suppression of the discharge-current low-frequency breathing mode oscillation.

Mode Transition of Trichel pulses

The trichel pulse is a typical kind of negative corona current observed in electronegative gases. In this work, stochastic behavior of the trichel pulse has been investigated. The experiment is performed in a negative corona reactor consisting of a stainless steel pin and a stainless steel powered by a dc high voltage source. The characteristic parameters distributions of corona current pulses, including the amplitude, rise time, half-wave time, and repetition frequency, are analyzed statistically. The results show there is a mode transition during the period of voltage increasing. This transition process happens in a certain voltage region, and change of pulse amplitude is the main difference between the two modes.