Displacement damage effects in mixed particle environments for shielded spacecraft CCDs

Analysis of monoenergetic proton test data reveals displacement damage degradation of charge transfer efficiency in state-of-the-art CCDs. New measurements, in combination with literature data, demonstrate good agreement between the energy dependencies of proton damage and the nonionizing energy loss (NIEL) for protons in Si. Massive shields being considered to preserve CCD performance in satellites are then analyzed using the transport code BRYNTRN which quantifies both primary and secondary particle production. Using NIEL to combine the cumulative effects of both protons and neutrons reaching the CCD, the authors compare Al and Ta shield approaches for both trapped and flare proton environments. In general, massive Ta shields have diminished benefit owing to damage from large secondary neutron fluxes. Finally, analysis with Shockley-Read-Hall theory illustrates the importance of CCD operating conditions and transfer efficiency measurement techniques in evaluating flight performance and comparing results between devices and laboratories