Electrostatic Discharge Characteristics Of Polyimide Films Under Electron Irradiation

In the space environment spacecraft insulation materials tend to accumulate electric charge,triggering electrostatic discharge phenomenon.Severe electrostatic discharge can cause insulation failure and affect the normal operation of space equipment.The space environment is complex,and the characteristics of electrostatic discharge generated by irradiation with different electron energies and beam densities and their continuous effects may be different.Therefore,it is important to study the electrostatic discharge characteristics of dielectric materials under electron irradiation.Based on the geosynchronous orbit operation environment,the laboratory’s existing electron gun based on the principle of hot electron emission is improved to achieve continuously adjustable electron energy(0～50 keV)and beam density(0～8 nA/cm2).The electrostatic discharge current measurement device was built,combined with vacuum and temperature control system,surface potential measurement module and surface leakage current measurement module,to construct a medium electrostatic discharge measurement system under electron irradiation,to record the medium electrostatic discharge current and surface leakage current under electron irradiation in real time,and to measure the medium surface potential distribution before and after the medium electrostatic discharge.The electrostatic discharge current measurement was carried out on polyimide films at 15 keV and 0.33 nA/cm2 for a cumulative duration of 132 h.The characteristic parameters of the discharge were extracted and plotted.It is found that the electrostatic discharge process of polyimide film under continuous irradiation consists of three stages,which are Ⅰ,Ⅱ and Ⅲ stages in order.The distribution of discharge characteristics shows that the discharge volume is large in the Ⅰ stage and the discharge time interval is short;the rise time,wavefront time and duration of electrostatic discharge current are short in the Ⅱ stage;the dispersion of electrostatic discharge characteristics is high in the Ⅲstage,and the waveform characteristic parameters are large,the discharge volume is small and the discharge time interval is long.The surface potential measurements showed that the surface potential distribution of stage Ⅰ was single-peaked,that of stage Ⅱ was multi-peaked,and that of stage Ⅲ was alternating between flat-topped and cratered.The electrostatic discharge characteristics of polyimide films with different electron energies(12 keV,15 keV,20 keV)and beam densities of 0.33 nA/cm2 and irradiation times of 48 h were investigated.With the increase of irradiation electron energy,the onset of the discharge phase was advanced,the number of discharges increased,the average discharge interval decreased,the amount of discharge increased,and the half-peak time decreased,while the rise time,wavefront time and duration of electrostatic discharge did not change much.In the late stage of irradiation,the discharge with high electron energy and high power is more likely to form a long discharge interval,while the long discharge interval with low electron energy is more likely to cause a large discharge volume.The electron energy elevation makes the three-dimensional pattern of the number of discharges with time interval more aggregated,and the discharge peaks move to the high discharge area and shift from single to double peaks.Combined with the surface potential and surface leakage current measurement results,the analysis concluded that the electron energy change has a small effect on the potential distribution pattern,but the discharge characteristics change accordingly because it affects the electron injection process.