Design And Experimental Study Of Micro Radio-Frequency Plasma Cathode-Neutralizer

The specific impulse of electric thruster which has the features of simple compact structure and light quality,is much higher than that of chemical rocket thruster.So the electric thruster is used more and more in space missions,especially in satellite with free control,station keeping,gravity field measurement and so on.RF ion thruster has the highest specific impulse and thrust efficiency among electric propulsion systems in practical use.However,in order to accomplish some tasks,long continuous operation of several years is required.As the core component of RF ion thruster,the main function of the neutralizer is the emission of the electron,which is used to start RIT and neutralize the plasma plume,keep the satellite potential neutral.Hollow cathode is used most widely at present,however because of its slow starting time and limited lifetime by degradation and depletion of an oxide insert,so a new type of neutralizer should be required.Due to instantaneous ignition,oxide-insert-less and simple handling,radio-frequency neutralizer is gradually favored.Based on the foreign literature,an experimental RFN with 2cm in inner diameter and 3cm in height has been fabricated,which enables ignition and emit electrons.The main part consists of discharge chamber,collector,keeper,coupling antenna,starting filament,shielding shell and so on.The test is in the vacuum environment.Inductively coupled mode is the best choice for the power coupling and L matching network is chosen to provide maximum power transfer.The materials of cathode and anode are graphite,which is preventing plasma sputtering effectively,high temperature resistance and long lifetime.The induction coil:hollow copper wire,the discharge chamber:the quartz with the smaller composite coefficient,the gas nozzle:PFTE,the shielding shell:aluminum alloy,which has many small holes.In the preliminary ignition experiment,the RF-discharge power is 15W and the emission of the electron current can reach tens of mA at the radio frequency is 2.8MHz with Xe.A 2cm cylindrical radio-frequency neutralizer is designed and ignition test is conducted many times in the selected frequency.The adjustment of the matching network and parameters of gas pressure are very helpful to optimize subsequent design.