Evolution of dielectric surface potential induced by electron beam radiation

Abstract

<p indent=0mm>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, Al₂O₃, and ZnO, and extracted the two critical energies (<italic>E</italic>₁ and <italic>E</italic>₂, where the SEY value 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 × <sc>10⁻⁹ A,</sc> the diameter of the electron beam spot is 1 × <sc>10⁻⁸ m,</sc> the width of a single pulse is 0.9 × <sc>10⁻⁹ s,</sc> and the period duration of a single pulse is 1 × <sc>10⁻⁹ s.</sc> 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 (<italic>E</italic>_p) 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 <italic>E</italic>₁ and <italic>E</italic>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 (<italic>E</italic>_p><italic>E</italic>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 (<italic>E</italic>_p><italic>E</italic>₂) is relatively high and its magnitude can reach <sc>10000 V;</sc> 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 (<italic>E</italic>₁<<italic>E</italic>_p<<italic>E</italic>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 <italic>E</italic>₂ value exhibits a lower negative balanced surface potential and a long balanced duration, and this property makes the dielectric material with a high <italic>E</italic>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.