电子束辐照诱导介质表面带电演化过程

Evolution of dielectric surface potential induced by electron beam radiation

空间环境中航天器介质表面的充放电现象是在轨航天器工作中面临的重要可靠性问题,开展介质表面充放电动态过程研究对于揭示带电机理、开展带电防护研究至关重要.本文推导了介质表面电子发射行为对表面带电类型和带电水平的影响规律,通过仿真建模模拟了恒定能量电子束辐照介质时的表面电荷积累过程,获得了氧化镁、氧化铝、高阻氧化锌3种介质表面电位演化过程的动态规律.结果表明,如果电子束能量低于二次电子产额曲线中第二临界能量,则辐照诱发的表面负带电或正带电的平衡电位较低,仅为几十伏;而高于第二临界能量的电子束辐照诱发的表面负带电水平可达上万伏;具有高第二临界能量的介质材料的负带电水平相对较低且充电速率较为缓慢,是减缓介质表面充电过程、实现带电防护的理想材料.本研究详尽论述了单一能量电子束辐照下介质表面电位演化过程的动态规律,对于进一步开展介质表面带电水平分析和抑制带电研究具有重要意义.

Spacecrafts operate in a complex space plasma environment and are constantly exposed to cosmic ray radiation.The charging and discharging phenomena that occur on the dielectric surfaces result in major reliability issues for the spacecraft’s normal operation.Secondary electron emission(SEE)caused due to electron radiation is the primary inducement of dielectric surface charging,and the SEE level severely affects the charging and discharging status.In this paper,to discover the dynamic evolution process of dielectric surface charging under the circumstances of electron beam irradiation,we have conducted a systematic study on the surface potential and SEE behaviors under various irradiation situations.First,we fitted the secondary electron yield(SEY)curves for three dielectric materials with high resistance,namely MgO,Al_(2)O_(3),and ZnO,and extracted the two critical energies(E_(1) and E_(2),where the SEYvalue equals 1 for the first and second time,respectively),SEY peak values,and the corresponding primary electron energy of the SEY peak value from the three SEY curves.Then,for the situation of electron beam radiating dielectric materials,we developed a physical model and simulated the dynamic evolution processes of the dielectric surface potential.The radiation source is a pulsed electron beam,and some radiating conditions include the following:The intensity of the beam current is set as 1×10^(−9) A,the diameter of the electron beam spot is 1×10^(−8) m,the width of a single pulse is 0.9×10^(−9) s,and the period duration of a single pulse is 1×10^(−9) s.We calculated the charge accumulating amount after pulse radiation and the corresponding variation quantity of the surface potential based on these assumed radiation parameters and the ideal charging situation without charge leakage.We discovered the evolution regularities of the potential variation rate,potential level,and potential balanced duration for the three irradiated materials by calculating the transient surface potential.Furthermore,we have simulated the dependence of surface potential on the radiation energy(Ep)of the electron beam.Several conclusions are summarized by analyzing the simulation and calculation results.First,the SEE characteristics of dielectric materials,particularly the two critical energy values E_(1) and E_(2),are the two key factors that affect positive or negative charging,as well as the balanced duration and balanced surface potential level.Second,the negative balanced surface potential induced by low energy electrons(Ep>E_(2))is only a few tens of volts;the balanced time is a few hundred pulses,and the surface potential variation rate first increases and then decreases.Third,the negative balanced surface potential induced by the high energy electrons(Ep>E_(2))is relatively high and its magnitude can reach 10000 V;moreover,the balanced duration is relatively long(about several tens of thousands pulse duration).Fourth,because the positive balanced surface potential induced by the middle energy electrons(E_(1)<Ep<E_(2))is extremely low,and the balanced time is short(less than a few tens of seconds),the variation rate of the positive surface potential rapidly decreases.Fifth,the dielectric material with a higher E_(2) value exhibits a lower negative balanced surface potential and a long balanced duration,and this property makes the dielectric material with a high E_(2) value play a more significant role in the suppression of surface charging.In this paper,we have discussed in detail the dynamic evolution regularities of surface potential when the dielectric is irradiated by an electron beam,which is beneficial for further analysis about dielectric surface charging,discharging,and further research on the charging defense.