Modeling of proton-induced CCD degradation in the Chandra X-ray Observatory

Modeling results are presented for proton-induced degradation of charge-coupled devices (CCDs) used in the Advanced CCD Imaging Spectrometer instrument on the Chandra X-Ray Observatory. A methodology is described that provides insights regarding degradation mechanisms and on-orbit performance for front-illuminated and back-illuminated CCDs. Proton-induced changes in charge transfer inefficiency are modeled. The observed amount of on-orbit degradation can be accounted for using a proton spectrum at the CCD location that has the same shape as the spectrum incident on the spacecraft but has a fluence that is reduced in magnitude by a factor of ∼10⁵.