The Cosmic Origins Spectrograph FUV detector.

The Far Ultraviolet (FUV) detector for the Cosmic Origins Spectrograph (COS), scheduled to be installed in the Hubble Space Telescope in June 2003, is currently being built by the Experimental Astrophysics Group at The University of California, Berkeley. The COS FUV detector system is based on the detectors flown on the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite with changes to take advantage of technological improvements since the development of those detectors. The COS FUV detector is a dual segmented, cylindrical input face, MCP detector with cross delay line (XDL) readouts. Each segment is a Z-stack of MCPs with an active area 85 mm by 10 mm. The segments are abutted end to end to form a total active area approximately 180 mm by 10 mm (with a gap in the middle). Detector spatial resolution in the long (spectral) dimension is better than 25 microns and in the short dimension (cross-dispersion) is better than 50 microns. The MCPs are coated with a CsI photocathode to achieve the optimal quantum detection efficiency (QDE) in the 1150-1750 angstrom bandpass. Improvements in the understanding of the processing required to produce higher QDE MCPs has lead to significant improvements in the FUV QDE relative to previous missions. This paper presents the basic design parameters and performance characteristics of the COS FUV detector.