Study On Flashover Characteristics Of Polyimide Along The Surface Under Electron Irradiation

Aerospace equipment in the space environment during operation,its surface will be bombarded by charged particles in space,spacecraft used insulation materials with high resistance characteristics,resulting in the space environment radiation electrons in the incident into the insulation material is difficult to be conducted and released,thus forming a high surface potential and self-built electric field,incident into the material at different depths of electrons and lead to different degrees of electric field distortion,in spacecraft some typical structures,such as solar cell wings,The electric field distortion of the insulating material will greatly affect the insulation performance between the horizontally arranged battery cells,increase the risk of discharge and flashover,and affect the normal operation of the spacecraft in orbit.Therefore,it is of great significance to study the flashover characteristics of insulating materials under the conditions of electron irradiation.Based on the operating environment of spacecraft in space low earth orbit,this paper builds an experimental platform for flashover testing along the surface under electron irradiation,simulates the internal spatial charge distribution and electric field intensity distribution of insulating materials under electron irradiation in combination with working conditions,and proposes an experimental scheme for flashover testing along the surface with reference to relevant test standards,and conducts flashover tests along the surface of polyimide with a thickness of 200 microns under different irradiation conditions,and explores the deposition charge,Effect of hole and electron beam flow charge at the bottom of material on flashover characteristics of polyimide along the surface.The simulation shows that under the vacuum-insulating medium-suspension electrode structure,the surface charge deposition is relatively large,the charge migration is relatively shallow,and the tangential electric field strength on the surface of the material is the largest at the vacuum-material-electrode junction.Under the vacuum-insulating medium-grounded electrode structure,there are holes at the bottom of the material,the charge deposited on the surface of the material is relatively small,and the inward migration is deeper,and the tangential electric field strength on the surface of the material at the three-junction point of vacuum-material-electrode is increased more than that of the vacuum-insulating medium-suspension electrode structure.Under the two structures of vacuum-insulating medium-grounding electrode and vacuum-insulating medium-suspension electrode,the polyimide film was pre-irradiated for different durations,and the flashover test along the surface was carried out after the irradiation stopped.When only the surface deposition charge exists and the deposition charge is less,the deposited charge has a weakening effect on the field strength at the cathode three junction points,so that the flashover voltage increases,and with the increase of the deposited charge,the probability of local microdischarge(pre-flashover)on the surface of polyimide increases,which promotes the development of flashover and reduces the flashover voltage;In the vacuum-insulating medium-grounded electrode structure,holes are generated at the bottom of the material due to the withdrawal of the charge,and the flashover voltage in the actual experiment under these conditions is significantly lower than that without holes.Under the conditions of no preset irradiation and vacuum-insulating medium-suspension electrode structure,the flashover voltage of polyimide along the surface under different irradiation parameters and different electron beam incidence angles was measured,and it was found that the flashover voltage decreased with the increase of electron energy or the decrease of incidence angle.The simulation results show that with the increase of electron energy or the decrease of incidence angle,the electron beam flow charge may participate in the flashover process "earlier".As the beam density increases,the electron beam flow charge will participate more in the flashover process,promote the development of flashover,and the flashover voltage will also decrease.