HEATER OF THE HOLLOW CATHODE WITH LaB6 FOR OPERATION WITH HALL THRUSTERS
The article presents the results of design, development and laboratory tests at Space Electric Thruster Systems (Dnipro, Ukraine) of a hollow filament cathode based on lanthanum hexaboride (LaB6). The cathode is designed for joint operation with Hall thrusters of various input powers. The emitter material LaB6 is very promising, because has a high emissivity and low ionization potential. However, to realize all the advantages of considerate material, it is necessary to provide a sufficiently high operating temperature (1400 ° C). Therefore, when developing the filament cathode, special attention was focused on the development and research of one of the key elements of the filament cathode - the heater. Thermal calculations of the hollow cathode were carried out when it was heated with a heater, as well as when the cathode was operating in auto mode. The results of thermal calculations made it possible to identify the shortcomings of the cathode structure and parameters and determine the ways to eliminate them. Laboratory tests of a cathode with a different number of heater thermal shields have been carried out. The results obtained made it possible to provide the required operating temperature of the cathode emitter with a minimum number of heat shields. Laboratory tests of the cathode were carried out both in diode mode (to the external anode) and in conjunction with the ST-25 Hall thruster developed by the company. In the course of laboratory tests of the cathode, the power supplies for the discharge, the keeper, and the heater, which are components of the power processing unit of the Hall thruster, were used. In the frame of experimental studies, a cyclogram of the cathode starting process was obtained, which is necessary to form the Hall thruster starting sequence. The tests carried out confirmed the correctness of the selected technical solutions for the choice of the cathode and its heater. The developed cathode can be used both in low-power (up to 200 W) Hall thrusters and in thrusters with increased input power (up to 5 kW).
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