  After launch, the Advanced CCD Imaging Spectrometer (ACIS), a focal plane
instrument on the Chandra X-ray Observatory, suffered radiation damage from
exposure 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, the
focal plane was warmed from the operating temperature of -100C to +30C which
unexpectedly further increased the CTI. We report results of ACIS CCD
irradiation experiments in the lab aimed at better understanding this reverse
annealing process. Six CCDs were irradiated cold by protons ranging in energy
from 100 keV to 400 keV, and then subjected to simulated bakeouts in one of
three annealing cycles. We present results of these lab experiments, compare
them to our previous experiences on the ground and in flight, and derive limits
on the annealing time constants.
