Dielectric discharge of PI material irradiated by 40 MeV-protons

Deep dielectric charging and discharging by electrons has been known for years. However, deep space missions towards the Moon, Mars and Jupiter have developed these years. In these space environments, spacecrafts would expose in high fluxes of solar energetic protons which demands the understanding of charging and discharging mechanism by protons. In this paper, dielectric breakdown of polyimide(PI) material irradiated by 40 MeV-protons was studied. Discharge of PI materials with different thicknesses of $21.5\mathrm{mm}$, $15.5\mathrm{mm}$, $13.6\mathrm{mm}$ and $8.2\mathrm{mm}$ were investigated. For PI films with thickness of $21.5\mathrm{mm}$, $15.5\mathrm{mm}$, and $13.6\mathrm{mm}$, proton discharges were firstly triggered as the protons reached integral fluxes of $1.2\times 10^{12}p/{\mathrm{cm}}^2,2.7\times 10^{12}p/{\mathrm{cm}}^2$ and $1.2\times 10^{12}p/{\mathrm{cm}}^2$, respectively. No discharge was achieved for PI film with $8.2\mathrm{mm}$ thickness. Besides, discharge events originated by secondary electrons were also achieved during irradiation.

On the other hand, the internal potential and electric field was also simulated using simulation of internal charging software for 3D (SIC3D). Simulation results indicate that discharge threshold caused by protons is decided by two factors: the internal electric field and the length of discharge path. After irradiated by protons, a thicker material might store more protons and produce stronger internal electric field, but might also has a longer discharge path. The integral proton flux required for discharging was $10^{12}p/{\mathrm{cm}}^2$ which is extremely high in real space conditions, and proton discharge may not happen immediately after irradiated by energetic protons in space. But the stored protons can produce a localized electric field and might be triggered during the next space radiation events like the solar energetic particle (SEP) events or the bursts of energetic electrons (BEE) events.