Radiation damage testing status of the CCDs for the SMILE SXI

The joint European Space Agency and Chinese Academy of Sciences Solar wind Magnetosphere Ionosphere Link Explorer mission (SMILE) aims to develop a global scale understanding of the interaction between the solar weather and the Earth’s magnetosphere-ionosphere. The soft X-ray imager (SXI) is one of the instruments on board and will observe photons emitted in the 200 eV to 2000 eV energy range from the solar wind charge exchange process using two large 4510 x 4510 pixel CCD370s as a focal plane. The CCD370s take their design and qualification heritage from similar sensors being used in the PLATO mission, with specific modifications to optimize their performance in this soft X-ray energy range. SMILE will orbit Earth in a highly elliptical orbit and will pass through the radiation belts every 52 hours. The trapped and solar protons present will gradually damage the CCDs throughout the 3-year mission and degrade their performance. To understand the impact the damage has on the devices a series of proton radiation campaigns are being undertaken. These campaigns are being performed with flight-like SMILE CCDs, and functionally similar PLATO devices, with follow-up characterization across from -130 to -85 °C. The most recent irradiation campaign has been completed using a PLATO CCD280 kept below -85 °C for irradiation and characterization, and the results show that the measured parallel charge transfer inefficiency varies with temperature between 1x10-4 and 4x10-4 in unbinned full-frame readout mode. The effect of temperature annealing up to -85 °C on the parallel charge transfer inefficiency has also been assessed and shows that no temperature-dependent annealing of the radiation-induced damage has been observed. A similar behavior is expected to be seen in the SMILE devices, albeit with an anticipated improvement by a factor 3-4 due to the modifications made to the design. Thus, results indicate the SMILE CCD370s will meet the performance requirements of the SMILE SXI instrument.