Study of H-recombination in Aluminium foils: first irradiation tests with low-energy protons (5 keV) at the DLR Complex Irradiation Facility (CIF)

Kurzfassung

The current DLR project GOSSAMER aims at establishing solar sails as a powerful and reliable propulsion technique for future space missions. The solar sail propulsion technique basically uses the transfer of momentum from solar photons to a large foil which has been deployed in space and is connected with a payload. The latest design of the GOSSAMER solar sail will use a thin polyimide foil covered on both sides with a 100 nm layer of Aluminium. However, the aging of the foil in a space environment, especially changes in the specular reflectance of the surface, has to be studied very carefully to ensure a proper performance of a solar sail spacecraft over long mission periods. One possible degradation effect is presented: the blistering of the Aluminium surface under proton irradiation. Protons that were stopped in a metal can recombine with free electrons to H-atoms and can finally form bubbles of H2 within in the material. It depends on several parameters whether this recombination leads to the formation of blisters at the surface of the metal: the energy of the protons, the proton dose, the thermal conditions, the solubility of hydrogen in the metal, impurities, and defects in the material. Previous published laboratory studies showed that blisters on Aluminium surfaces occur at relatively low proton energies (< 100 keV) and high dosages (1016 to 1018 protons/cm²).