Physics of reverse annealing in high-resistivity Chandra ACIS CCDs

摘要

After launch, the Advanced CCD Imaging Spectrometer (ACIS), a focal planeinstrument on the Chandra X-ray Observatory, suffered radiation damage fromexposure to soft protons during passages through the Earth's radiation belts.An effect of the damage was to increase the charge transfer inefficiency (CTI)of the front illuminated CCDs. As part of the initial damage assessment, thefocal plane was warmed from the operating temperature of -100C to +30C whichunexpectedly further increased the CTI. We report results of ACIS CCDirradiation experiments in the lab aimed at better understanding this reverseannealing process. Six CCDs were irradiated cold by protons ranging in energyfrom 100 keV to 400 keV, and then subjected to simulated bakeouts in one ofthree annealing cycles. We present results of these lab experiments, comparethem to our previous experiences on the ground and in flight, and derive limitson the annealing time constants.