Research On The Configuration Of Low-power Cylindrical Hall Thruster

Recent years,the rapid development of small satellite in deep space fields motivates the micro-propulsion.In many kinds of propulsion devices,Hall thrusters have been widely developed for the high specific impulse and low propellant consumption,at the input power range from sub-kilowatt to tens of kilowatts.However,scaling down the conventional Hall thruster could lead to the large surface-to-volume and the lack of the inner pole room,which could not only increase the difficulty of thruster assembly technique,but also lead to a series of problems,such as the overheat,magnetic saturation and the wall erosion.Ultimately,the thruster lifetime could be affected significantly.To solve these problems,Raitses developed cylindrical Hall thrusters,which have lower surface-to-volume ratio by cutting down the inner magnetic pole and forming a cylindrical discharge channel.At present,various cylindrical Hall thruster-types have been researched in USA Japan Korea and China,and the test results show that CHT features the high propellant utilization,quiet operation and performance comparable with the same size conventional coaxial Hall thruster.During the reference survey of the low-power cylindrical Hall thruster,it is concluded that there are three general aspects problems as following:the plume shape tend to be divergent and the plume angle are often over 60°;the current utilization tend to be larger than 70%;In addition,the scaling of thruster channel aggeravate the anode over-heat and affect the stable operation at high voltage.In fact,these problems should be related with the ionization and acceleration process intimately.However,lack of the acknowledge for these physical process,nevertheless,it is also inadequate for the understanding of electric field structure in the miniaturized cylindrical Hall thruster.In fact,.the electric field is formed by the coupling of magnetic field and the magnetized electrons,thus,it is necessary to develop the research of the ionization and acceleration process through the magnetized electrons,transport and the corresponding magnetic field in the cylindrical Hall thruster.The anode and cathode play the important roles for the electron transport and electric field structure as they are the termination and start of electron transport,respectively.Therefore,the electrode location for cylindrical Hall thruster were developed in theory and experiment in this paper,including the effect of anode radial placement,cathode placement and cathode keeper current on the kinds of discharge characteristics,including electron transport,ionization and acceleration feature,plume characteristics and so on.In particular,during the study on anode radial location,a porous ceramic structure was employed as the gas distributor,which were separate from anode and make the anode being the single parameter.Based on this,the annular anodes with different radius were designed and the corresponding tests were operated.The results show that when the anode moves along the radial direction towards outer wall,the electrons tend to experience longer transport path,which lead to the pronounced reduction of electron current and inversely,the ion velocity tends to grow significantly.In addition,the rise of cathode keeper current could improve the collimation of plume.Secondly,as the target of ionization,the neutral gas play a significant role for the electron transport and ionization process in discharge channel.Therefore,the effect of radial position of gas holes in the distributor on the performance of cylindrical Hall thruster was investigated.A series of gas distributors with different radial position(Rg)of holes were designed in the experiment.The results show that the larger Rg leads to the higher ion current and electron current,meanwhile,the beam angle in plume is narrowed.Nevertheless,the peak energy in ion energy distribution function increases,together with the narrowing of ion energy distribution function.As a result,the overall performance are enhanced.It is suggested that the growing of Rg could lead to the movement of the main ionization region towards anode,which could promote ion velocity and the clearer separation of acceleration region from ionization region.This work can provide some optimal design ideas to improve the performance of the thruster.Thirdly,the anode overheat in miniaturized cylindrical Hall thruster is a important inducement for the plasma instability in discharge channel,This problem should be due to the strong magneitic field in the vicinity of anode,which could aggerevate the electrons'bombardment to anode.In this paper,the magnetic field near anode was weakened firstly to reduce the energy loss at the anode.Based on the divergent feature of magnetic field in cylindrical Hall thruster,two designs of weakening the near-anode magnetic field:on one hand,the magnetic shielding between anode and center pole were added to weaken the magnetic field near anode,during this process,the magnetic topology maintains almost constant;on the other hand,the inverse electromagnetic current near anode were added to weaken the magnetic field near anode,compared the former design method,this design could produce a zero magnetic field in the vicinity of anode,which means the lager decrement for the magnetic field near anode,together with the change of magnetic topology.The experiment results show that weakening the magnetic field near the anode is contribute to the enhancement of propellant utilization,the convergence of beam in plume and the narrowing of ion energy distribution,the ionization region is expected to extend toward the anode.As a result,the thrust and efficiency are enhanced significantly.In the last section,based on the aforementioned research on the thruster's electrode location,gas ways,the magnetic field near anode,a miniaturized cylindrical Hall thruster with a 3 cm channel diameter and 100?300 W power were designed and investigated.Compared with the similar size Hall thrusters in reports,the 3cm HCHT designed in this paper have a wider power range,from 150 W to 300 W.Nevertheless,the impulse in 3cm HCHT is higher than those of BHT-200 at 200 W anode power and the maximum profile reach 2000s,higher than the most cylindrical Hall thruster in resports.