GEANT4-based Numerical Simulation Of Internal Charging Protection For Spacecraft Dielectric

The spacecraft will suffer various threats from airspace and among these threats the deep dielectric charging and discharging effect caused by high energy electron radiation is an important reason for the abnormal operation or fault of the electronic equipment in spacecraft. The deep dielectric charging and discharging effect is always subject of great interest in the field of charging and discharging effect and protect technology of the spacecraft because it can impact strongly on the insulating properties of the dielectric material and even induce arc discharge, leading to the burning and breakdown of dielectrics, which presents a serious effect on the reliability and service life of the spacecraft. In recent years, it has been found that the non-linear conductance modification of the spacecraft dielectric can release the hazardous charges in lower electric field and hence decrease the charges in dielectrics. Therefore, it becomes an effective protective method for the deep dielectric charging effect.In this thesis, the research background, history and current status of spacecraft deep dielectric charging effect have been reviewed and the calculation methods for modeling deep dielectric charging have been summarized. These methods correspond mainly to the calculations of the electron transportation, dielectric conductivity, and electric field. GEANT4particle transfer simulation package is used to realize electron transportation in dielectrics and the differential equation model combined with radiation-induced conductivity and non-linear conductivity is used to calculate internal electric field of dielectrics. And deep dielectric charging of SiC/LDPE composite with different types, contents, crystal forms, and size of SiC is studied. In addition, the calculation examples for the distributions of electric field in the dielectrics are made and the calculated results are compared with those of the published literature, showing the reliability of the method used in this thesis.The studies in the thesis present the following results. The non-linear conductance modification of spacecraft dielectric can decrease the number of charges in dielectrics and prevent dielectric breakdown. With the increase of SiC impurity amount, the depth when the electric field gets stronger and the maximum electric field intensity become smaller. The improvement for deep dielectric charging by adding a-SiC/LDPE is better than that by adding green a-SiC/LDPE. The modification of deep dielectric charging with the addition of β-SiC presents more efficiency than that with the addition of α-SiC. When the a-SiC impurity amount increase up to37.5wt%, the increase of the size of SiC is beneficial to the decrease of the electrical field intensity. In addition, for the SiC/LDPE the impurity amount of SiC and its non-linear conductance are the dominant factor of influencing the electric field intensity in the dielectric. The results presented in this thesis are in agreement with those in the reported experiments and they can give effective reference for modification and insulation protect of the spacecraft dielectric.