Investigation of service life characteristics of hot cathodes in arc plasmatrons

Among the applied challenges associated with the use of electric-arc plasma, the most urgent is the erosion of electrodes in plasmatrons, which determine the continuous operation of an electric-plasma device. Investigation results on the thermal state of hot cathodes and their erosion are presented depending on the main defining parameters, namely geometrical dimensions of electrodes, Joule heating, current of the arc discharge, and the gas medium. The conditions for the minimum specific erosion and long service life of tungsten thermionic cathodes are established experimentally.

The possibilities of using a femtosecond fiber laser in the manufacture of thermionic cathodes

The possibilities of using a fiber laser with a femtosecond duration of radiation pulses in the manufacture of miniature thermionic cathodes made of 50 μm of tungsten-rhenium foil are shown. The cathode assembly, consisting of a heater and a core, is made in the form of a solid structure with an oxidecoating applied by ion-plasma sputtering. The emission characteristics of the cathode are presented.

Desorption from Hot Scandate Cathodes: Effects on Vacuum Device Interior Surfaces after Long-Term Operation

Scandate cathodes have exhibited superior emission properties compared to current state-of-the-art “M-type” thermionic cathodes. However, their integration into vacuum devices is limited in part by a lack of knowledge regarding their functional lifespan and behavior during operation. Here, we consider thermal desorption from scandate cathodes by examining the distribution of material deposited on interior surfaces of a sealed vacuum device after ~26,000 h of cathode operation. XPS, EDS, and TEM analyses indicate that on the order of 1 wt.% of the initial impregnate is desorbed during a cathode’s lifetime, Ca does not desorb uniformly with time, and little to no Sc desorbs from the cathode surfaces (or does so at an undetectable rate). Findings from this first-ever study of a scandate cathode after extremely long-time operation yield insight into the utility of scandate cathodes as components in vacuum devices and suggest possible effects on device performance due to deposition of desorption products on interior device surfaces.

Application of an additional electrode for improving the emission properties of the lossless cathode-neutralizer for EPSPS

The article considers the advantages of application of an additional electrode — anode-collector in the design of a lossless cathode-neutralizer (LCN) for electrically powered spacecraft propulsion systems (EPSPS) (hall-effect thrusters and ion thrusters). The relevance of the work is due to the increased interest in the possibility of using lossless thermionic cathodes as cathodes-neutralizers (CN) of EPSPS. Based on the results of laboratory tests of the lossless cathode-neutralizer model conclusions are drawn about the effectiveness of the anode-collector in the design of the lossless cathode-neutralizer. The presence of the collector-anode allows for additional “stimulation” of the emitter by voltage intensifying the emitter activation process and increasing the emission current from the emitter surface by 2-2.3 times. The saved energy for emitter heating due to using an anode-collector is estimated. The basic concepts and recommendations for the development of the design of lossless cathode-neutralizer design are presented.

Research of an oxide cathode as a cathode-neutralizer for EPSPS

In this research, a laboratory model of a thermionic oxide cathode was tested as part of a diode circuit. The ultimate goal of this work was to obtain the thermionic characteristics of the emitter of the laboratory model and to study the processes of emitter activation. The relevance of the study is due to the increased interest in the possibility of using thermionic cathodes as cathode-neutralizers for electrically-powered spacecraft propulsion system (EPSPS). During the experiment, the following parameters were recorded: the pressure in the vacuum chamber and the emission current to the anode-collector. The current of the emitter and the voltage applied between the anode-collector and the emitter were regulated. The gap between the emitter and the anode-collector was set before the beginning of the experiment and was 2 mm. The emission current was measured in the emitter temperature range from 600 °C to 1260 °C. The temperature of the emitter was controlled by infrared and optical pyrometers. In the course of the work, three emitter activation processes were identified: temperature, time and voltage. The processes of activation by temperature and time are widely known, in contrast to the activation process by voltage, for which there is currently no unambiguous theoretical explanation.