Modeling Contamination Migration on the Chandra X-Ray Observatory - IV

During its first 18 years of operation, the cold (about -60degC) optical blocking filters of the Advanced CCD Imaging Spectrometer (ACIS), aboard the Chandra X-ray Observatory, has accumulated a growing layer of molecular contamination, which attenuates low-energy x rays. Over the past several years, the accumulation rate, spatial distribution, and composition have changed. This evolution has motivated further analysis of contamination migration within and near the ACIS cavity, in part to evaluate potential bake-out scenarios intended to reduce the level of contamination. This paper, the fourth on this topic, reports the results of recent contamination-migration simulations and their relevance to a decision whether to bake-out the ACIS instrument.