EXPERIMENTAL STUDY OF THE RANGES OF STABLE OPERATION OF CATHODE-NEUTRALIZERS FOR HALL-EFFECT THRUSTER

Abstract

With the development of space exploration, the need for more advanced propulsion systems for spacecraft is growing. Electric propulsion systems (EPS) are the most promising for orientation and correction systems. The Hall effect thruster (stationary plasma thruster in Ukrainian and Russian literature) (HET) is one of the most efficient and promising EPS thrusters. The cathode neutralizer (cathode compensator in Ukrainian and Russian literature, hereinafter referred to as the cathode) is one of the main elements of the HET. The resource and stability of the HET operation depend on the cathode. Previously, they were limited to studying the operation of the cathode in several modes. This made it possible to find the best mode of operation. Testing more modes will make it possible to predict the nature of the HET operation with this cathode. Also, similar gas-discharge cathodes are used in thrusters with anode layer, for ion thrusters and as sources of plasma in ion-plasma technologies. A number of non-incandescent hollow gas-discharge high-emission cathodes of the same model were tested in the diode mode. The cathodes were tested without a keeper; instead of the HET anode block, its simulator was connected to the gas-discharge circuit. With the help of a vacuum system, the operating conditions of the cathode were simulated - the ultimate vacuum was not worse than 2∙10-5 Torr. Xenon was used as the propellant. To support and regulate the operation of the cathode, plant models of the system for storing and supplying the propellant, power supply and control systems were used. Voltammeters measured the discharge current and voltage. Flow meter measured the mass of the propellant supplied to the cathode. Optical pyrometer measured the temperature at the cathode near to the diaphragm. The characteristics (the dependence of temperature and voltage on current or flow rate with the fourth parameter set) of cathodes were obtained. The stability of the operation of cathodes in one mode and the characteristics of the cathodes were explored. When the current decreases, the voltage rises at first smoothly, and then a peak is observed. A shift of this voltage peak towards a lower current with an increase in consumption was observed. It is shown that the cathodes operate most stably at currents corresponding to the horizontal part of the current-voltage characteristic (from the side of high currents from the peak). The operation of a cathode with a defective emitter is demonstrated. The operation of the cathode, which was stored for a long time, therefore had changes in the emission properties of the surface of the emitter material, was demonstrated.