A position sensitive detector for SPIDR—a mission to map the cosmic web

Abstract

The primary goal of the Spectroscopy and Photometry of the IGM's Diffuse Radiation (SPIDR) mission is to detect and map the huge filamentary structures, the “cosmic web”, predicted to be present in the IGM. To accomplish this task the SPIDR instrument comprises six imaging spectrographs providing high-resolution spatial maps of IGM features in the critical OVI and CIV lines at both rest and red-shifted wavelengths. Each spectrograph uses a two-dimensional position sensitive microchannel plate detector to image UV dispersed by a normal incidence grating, encoding spectral and spatial information. Two-dimensional imaging is recovered by tomographic reconstruction of data from the slowly spinning spacecraft. The detector configuration utilizes an open faced microchannel plate stack coated with a UV photocathode. The conservative imaging requirements are met by a wedge and strip anode whose performance has been enhanced by using the image charge technique. Image charge provides a highly stable and predictable detector response which has enabled us to use software simulation to improve the linearity of the readout considerably.