Experimental Study on Discharge Characteristic of Dielectric Material Induced by Space High-energy Proton Irradiation

Spacecraft are usually exposed to complex radiation environments during in-orbit flight and are prone to the accumulation of large amounts of electrical charges on the surface and inside the materials. Continuous charge accumulation can induce severe electrostatic discharge events, which can cause damage to spacecraft systems and even jeopardize the success of the entire mission. The deep charge-discharge phenomenon inside dielectric materials is one of the important factors leading to operational failures of on-orbit spacecraft and even mission failures. Currently, the electron-induced dielectric charge-discharge phenomenon has been extensively studied. However, with the advancement of exploration in the Van Allen belts and deep space exploration missions to the Moon and Mars, galactic cosmic rays and solar proton events have gradually become the main radiation environments faced by spacecraft, and there is still a lack of research on the charging and discharging characteristics of proton-induced dielectric materials. In order to study the discharge characteristics of proton-induced dielectric materials, this study carried out a proton beam irradiation experiment with an energy of 40 MeV and an injection of 10¹⁰ cm⁻²·s⁻¹ using the proton accelerator facility at the National Space Science Centre of the Chinese Academy of Sciences (NSSC). Polyimide (PI) dielectric samples of 80 mm×100 mm with different thicknesses were placed in a vacuum target chamber system facing a 100 mm diameter titanium window and shielded with aluminium around the sample. The experiments were carried out under a vacuum of 10⁻⁴ Pa at room temperature, with the grounding electrode tightly fitted to the back of the dielectric material and grounded by connecting a wire to a Rogowski coil. The discharge signal inside the dielectric material was collected by the Rogowski coil and recorded by an oscilloscope. The experimental results show that the PI films with thicknesses of 21.5, 15.5 and 13.6 mm, respectively, show significant discharges after a cumulative proton integrated flux of 10¹² cm⁻², whereas no discharges are observed for the PI film with a thickness of 8.2 mm under the same conditions. This result may be attributed to the accumulation of more protons inside the thicker PI material, which leads to the enhancement of the internal electric field and is more likely to trigger the discharge phenomenon. The above results provide an important experimental basis and theoretical reference for further exploration of the reliability of spacecraft dielectric materials under the complex radiation environment in deep space.