ACIS-Cal-Progress-020403.html - 04/03/2002
Over the past few years, it has become apparent that the quantum efficiency of ACIS below about 1 keV is decreasing with time. The memo below gives many of the details of what's known about the effect, which is caused by the buildup of a contaminant on the optical blocking filter (an aluminized plastic film a few inches in front of the CCD chips). The Chandra Project is considering warming the ACIS camera (a so-called "bakeout") in an attempt to evaporate some of the contaminant, and restore a portion of the lost sensitivity at low energies. The Chandra project has decided that there is not sufficient information at this time to proceed with a December 2003 bakeout of the ACIS instrument. A task force from NASA-MSFC, industry, the Chandra instrument teams, and the Chandra X-ray Center has been working on the details of a possible ACIS bakeout for the past several months. The build-up of the contamination is slow. We have therefore decided further study of the risks and benefits of the bakeout would be warranted. We are also studying the optimization of the proposed temperature schedule. The task force is continuing to work on these issues and it is expected that a decision on a possible bakeout will be made in the next six months.
Last modified: 11/03/04
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