Innovative technologies on proton irradiation ground tests for space solar cells

Reduction of time and cost of proton irradiation tests on space solar cells are considered by adopting state-of-the-art proton beam technologies developed at the Japan Atomic Energy Agency (JAEA). An irradiation area of about 80mm × 40mm is achieved with excellent uniformity in current density by the uniform-beam formation technique which employs multipole magnets. The experimental result of 10 MeV-proton irradiation using this `flash' (nonscanned, short-pulse) technique indicates no significant difference in the degradation trend of InGaP/GaAs/Ge triple-junction space solar cells compared to the results using our conventional beam-scanning method. The uniform-beam-formation approach enables irradiation over a time duration that is about an order of magnitude less than that required for the conventional scanned spot beam. Development of laser-driven proton beams is also being conducted at JAEA in which divergent proton yields with broad spectra similar to the space environment are typical. Laser-acceleration of protons is the result of intense irradiation of thin foil targets (such as aluminum) by high power lasers. For proton spectra that adequately simulate the space environment many irradiation tests with different specified proton energies will be unnecessary affording great simplification of complex radiation degradation prediction such as the relative damage coefficient method or the displacement damage dose method. Ground tests with a suitable compact laser-driven source can also enhance access and experiment diversity for irradiation studies.