Long-term trends in strongradiationstrong damage of Chandra X-ray CCDs.pdfVIP

Long-term trends in radiation damage of Chandra X-ray CCDs C. E. Grant, M. W. Bautz, S. M. Kissel, B. LaMarr, G. Y. Prigozhin Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology Cambridge, Massachusetts 02139 ABSTRACT Soon after launch, the Advanced CCD Imaging Spectrometer (ACIS), one of the focal plane instruments on the Chandra X-ray Observatory, suffered radiation damage from exposure to soft protons during passages through the Earth’s radiation belts. Current operations require ACIS to be protected during radiation belt passages to prevent this type of damage, but there remains a much slower and more gradual increase. We present the history of ACIS charge transfer inefficiency (CTI), and other measures of radiation damage, from January 2000 through June 2005. The rate of CTI increase is low, of order 10−6 per year, with no indication of step-function increases due to specific solar events. Based on the time history and CCD location of the CTI increase, we speculate on the nature of the damaging particles. Keywords: Charge Coupled Devices, radiation damage, charge transfer inefficiency, Chandra X-ray Observa- tory, ACIS 1. INTRODUCTION The Chandra X-ray Observatory, the third of NASA’s great observatories in space, was launched just past midnight on July 23, 1999, aboard the space shuttle Columbia.1 After a series of orbital maneuvers Chandra reached its final, highly elliptical, orbit. Chandra’s orbit, with a perigee of 10,000 km, an apogee of 140,000 km and an initial inclination of 28.5◦ , transits a wide range of particle en