Characterization of the flight CCD detectors for the GOES N and O solar x-ray imagers

Abstract

A new Solar X-ray Imager (SXI) using back-illuminated, anti-blooming CCD technology will become part of the instrument complement on NOAA's GOES (Geosynchronous Orbiting Environmental Satellite) N and O spacecraft, with probable launch dates beginning in the 2004-2005 time frame. SXI N and O were developed under a NASA contract by the Solar and Astrophysics Laboratory at the Lockheed Martin Advanced Technology Center, and are currently being integrated into their respective spacecrafts by Boeing Space Systems. SXI N and O will each provide full disk images of the Sun from 0.2 to 1.2 keV (10-60 Å) through the combination of a grazing incidence telescope, bandpass filters, and an X-ray imaging CCD. The custom designed, back-illuminated CCDs were fabricated and initially tested by Marconi Technologies (formerly EEV Ltd, now e2v technologies), screened in visible light by the Mullard Space Science Laboratory, and fully characterized in both visible light and X-rays at LMSAL. By minimizing the field-free region within the CCD, the spatial resolution at low X-ray energies was significantly improved. The SXI CCDs also exhibit only very modest response changes as a result of solar X-ray exposure, based upon extended life tests. The flight CCDs meet or surpass all specifications for quantum efficiency (QE), spatial uniformity, defects, charge transfer efficiency, QE stability in vacuum, read noise, linearity, full well and dark current. A QE model based on earlier work with ion-implanted, laser-annealed CCDs provides a consistent picture of the CCD response from soft X-rays through far UV wavelengths.