An investigation of the radiation damage experienced by the CCDs on the Gaia focal plane

Ahmed, Saad (2023). An investigation of the radiation damage experienced by the CCDs on the Gaia focal plane. PhD thesis The Open University.

Abstract

The European Space Agency’s Gaia spacecraft was launched in December 2013 with the aim of making the largest and most precise map of the Milky Way by taking measurements of over one billion astronomical objects. It has a payload of 106 charge-coupled devices (CCDs) to help achieve its objectives. During the pre-flight testing phase of the mission, the non-ionizing energy loss (NIEL) radiation damage on the detectors was identified as a major factor that would affect the science goals of the mission. From analysis of the in-flight data, the degradation of the CCDs from radiation damage, measured as the charge-transfer inefficiency (CTI), was found to be significantly less than what was predicted from the pre-flight on-ground tests.

This thesis further investigates the radiation damage of the Gaia CCDs to more precisely understand the CTI behaviour; this helps to maintain credibility in the pre-flight tests and to better prepare for future space missions. Further in-flight data is analysed and a number of new insights are revealed about the data, related to differences in behaviour between device variants and the nature of radiation damage across Gaia’s focal plane. Different factors that have combined to result in the lower in-flight CTI measurements are also studied with analysis of on-ground data and the use of different simulation models to better understand the datasets. Finally, all these factors are combined together to make an assessment on the CTI differences between Gaia’s in-flight and on-ground CCDs and propose future testing to determine any additional sources of radiation.

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