Design And Research Of Field Emission Source In Neutralizer

The neutralizer is an important part of the electric propulsion system,the core of which is the electron source.At present,most electron sources of the neutralizer are hot cathodes or hollow cathodes.Although the technology of the devices is relatively mature,there are still some problems that are difficult to overcome.However,the field emission cathode has the advantages of simple structure,low requirements of working environment and so on,which ensures its great potential for application in small or miniature electric propulsion systems.In this dissertation,we studied the emission characteristics of the electron source of the neutralizer,grid capture rate,the reduction of the power consumption of the grid and the reduction of the ion bombardment of the cathode.The main contents are:(1)The carbon nanotube cathode was prepared for the traditional screen printing method.The emission performance of the carbon nanotubes was tested.Under DC test conditions,the maximum current of the carbon nanotubes was 21.4 mA,whose corresponding emission current density was 2.73 A/cm~2(diameter 1mm).Under the condition of anhydrous cold,the system increased getter,.the maximum pulse current of the pulse test was 36.5 mA,corresponding to a current density of 4.65 A/cm(diameter 1mm).(2)Reducing the capture rate of the cathode electron beam on the grid to reduce the power consumption of the grid.Studying emission characteristics of the conventional field emission triode structure,when the cathode size of the carbon nanotubes was larger than0.25mm,simulation results that the interception rate of the grid electron to the cathode was about 48%,the experimental results that the interception rate of the grid electron to the cathode was about 52%.(3)The double-grid quadrupole structure and the side-cathode structure that were designed based on the conventional field emission triode structure greatly reduce the interception rate of the gate electrode to the cathode electron beam.In the experimental test,the dual-gate field emission structure had a grid capture rate of 10%under low current emission and 38%under high current emission.The side-cathode structure experimental test showed that the grid capture rate was only 23.8%.the gate capture rate of the side-cathode structure was 14.2%lower than that of the double-gate structure.(4)By simulation,the smaller the number of ions hitting the cathode surface is,the smaller the cathode sputtering yield is.a layer of shielded electrode structure was added on the basis of the field-emission triode structure.As a result,the impact of ion bombardment on the bombardment of the cathode can be effectively reduced.Combined with the simulation calculations,the relevant field emission experiments were carried out.The effect of the shielding electrode was verified by the gas filling method.The screening electrode can effectively reduce the impact of ion bombardment on the carbon nanotube cathode.Besides,the lower the shielding electrode voltage was,the better the shielding ion effect was.The experiment tested the intensity of the ion current of the shielding electrode under different pressures.The results showed that the strength of the shielding ion current increased with the increase of pressure and was proportional to the pressure,which provided a method for designing the structure of the electron source of the carbon nanotube fieldemission neutralizer.