Research On Decoupling Ignition Of Heaterless Cathodes And Optimization Method Of Ignition Lifetime

As electron sources and neutralizers,hollow cathodes are widely used in various space missions.Heaterless hollow cathodes remove heaters which limit the lifetime of cathodes and improve the life reliability.During multiple ignitions,a series of problems such as ignition failure,larger aperture,and ignition difficulty after cathodes exposured to the atmosphere have occurred.The coupling ignition is not conducive to decoupling analysis and there is large current shock in this ignition.The choice of coupled ignition strategy also has blindness.In order to solve the above problems,to ensure the reliability of the heaterless hollow cathode ignition and improve the ignition life,the following research has been carried out in this paper:Considering the ignition mode of the single cathode during decoupling ignition,a special study was conducted on the single cathode keeper-ignition characteristics.Use the oscilloscope to capture the ignition waveform and change in pressure and combine the high-speed camera to capture the ignition process.Two different single-cathode ignition modes,anode-ignition and keeper-ignition,were compared,and the ignition phase was re-divided into three phases.The key phases of ignition that affect the success of ignition were focused on and the influence of ignition parameters and circuit parameters on this stage was studied.Large ignition flow rate and discharge current preset will ensure a stable transition at key phase and reduce ignition shock.Large ignition voltage,large discharge voltage and external capacitors will bring more fluctuations to the key phase and increase the ignition shock..The effects of variable orifice size of the tungsten top,the keeper plate and the the emitter was studied by artificial reaming operation.The discharge waveform,change in pressure,and high-speed camera results were combined with COMSOL simulation to analyze the effects of larger aperture during long lifetimes.The larger tungsten top aperture leads to a decrease in the density of the plume plasma during the ignition process and an increase in the electron temperature,which is conducive to ignition but increases the steady-state discharge voltage.The larger keeper aperture reduces the plasma density at the initial stage of ignition,reduces the electron temperature in the tungsten top region,increases the ignition difficulty,and improves the ignition stability.The larger inner diameter of emitter increases the ignition shock and increases the ignition difficulty.For cathodes requirements of space missions,the expansion of the cathodeignition life was studied by means of utilizing an external heater.The decoupling analysis of the heater and the cold cathode ignition was carried out to prove the feasibility of the two ignition modes of the cathode with the heater,and the influence of heating on the cold ignition was studied.Heating will significantly improve the ignition difficulty after cathodes exposured to the atmosphere,reduce current impact during the cold ignition,expand the cathode ignition boundary,and effectively improve the cold ignition life.Two different thruster ignition modes were studied by the discharge current waveform acquired by the oscilloscope and the saturation electron current signal collected by the probe.It shows that the separated ignition can reduce the ignition shock.The influence of different ignition parameters was studied for the separated ignition mode,and the reasonable range of each parameter was pointed out.It is proposed that the separated ignition method of turning on the anode voltage after the first flow rate supply and the ignition of cathodes can reduce the ignition shock and improve the consistency.