Low Energy Design of the National Ignition Facility’s Soft X-ray Opacity Spectrometer

The soft x-ray Opacity Spectrometer (OpSpec) used on the National Ignition Facility (NIF) has recently incorporated elliptically shaped crystals. The use of an elliptically shaped crystal allows an acceptance aperture at the crossover focus between the crystal and the detector, which reduces background and eliminates nearly all reflections from alternate crystal planes. The success of the original elliptical geometry in the opacity experiments has driven the design of a new elliptical geometry with a spectral range of 520-1100 eV. Coupled with the original elliptical geometry the new lower energy ellipse can cover the full iron L-shell and major oxygen transitions that are important to solar opacity experimentation. The new design has been built and tested on a Henke x-ray source, showing the desired spectral coverage. Recently the new geometry has been fielded on NIF opacity experiments. The new geometry, Henke testing, and preliminary results from opacity experiments are presented.