1. Analysis of experimental data the model is based on
In the course of experimental research of characteristics and stationary plasma thruster (SPT) parameters, one of the goals was to find optimal modes of its operation that would be characterized by the minimal average value of the discharge current and the minimal amplitude of oscillations at a given mass flow of the propellant [1, 2]. This ensures minimal energy expense on creation of the thrust and reduces the requirement to the power of the discharge power supply unit. Preliminary experiments showed that the determining factors in achieving the optimal operational modes are the choice of the current in the electromagnet, as well as the choice of structure and optimal parameters of the output filter of the discharge power supply unit. The results of the experimental research of an SPT100 thruster, corresponding to the optimal structure and parameters of the output filter and put into the foundation of the synthesis of a mathematical model of the SPT, are shown in Fig. 1 . This figure shows dependences of the amplitude of the discharge current oscillations Ip and the average value of the discharge current Id on the value of the current Im in the electromagnet at different values of Vp. The dependence is extremal in its nature, which is preserved over different operational modes of the thruster and the change of the structure and parameters of the output filter of the power supply source.
Along with the determination of the static parameters of the SPT100
thruster, its dynamic characteristics were determined, which were obtained in
the form of spectra of oscillations of the discharge current at different
values of the current in the electromagnet . The obtained spectra
characterize the alternating component of the discharge current
The frequencies of the registered oscillations are in the range from 1.0 to 400
kHz. The main power of oscillations lies in the range of up to 120 kHz, where
the main peaks of the discharge current oscillation spectrum are located. With
the decrease of the current in the electromagnet from 4.5 A to 2.6 A,
the amplitude of the peaks sharply decreases (by 20 dB).