XUV calibrations and electron background reduction for the ROSAT Wide Field Camera
The ROSAT Wide Field Camera (WFC) is an imaging experiment, conducted by a consortium of UK groups, intended to perform the first all sky survey in the XUV wavelength band (6-30nm). As part of the development and flight programmes, XUV calibration and background simulation work has been undertaken at Leicester. Here, the commissioning and development of an XUV line source and monochromator is described and their use to produce a laboratory detector standcird is reported. Subsequent efficiency calibration of a Csl coated prototype WFC MicroChannel plate detector is reported and the results shown to be in substantial agreement with a published model of photocathode behaviour. The results fill a gap in the published data between 11.2 and 25.6nm. Reflectivity measurements on the Wolter-Schwtirzschild Type 1 grazing incidence mirrors are reported and compared with the predictions of theory and with published measurements on test flats. Differences between theoretical reflectivities and the empirical results of up to 15% axe shown to be consistent with either: low density reflective gold coating, hydrocarbon contamination, or errors in the optical constants assumed for gold. Measurements were found to be broadly in agreement with published results. In addition to experimental work, the impact of the orbital low energy electron background is assessed on WFC performance and shown to be limiting due to the inclination of the spacecraft orbit. Reduction of this background is shown, by computer simulation, to be feasible by the introduction of a magnetic screen. Preliminary electron beam tests support this view.