Lynx grating spectrometer design: Optimizing chirped transmission gratings

Kavli Affiliate: Ralf K. Heilmann

| First 5 Authors: Hans Moritz G√ľnther, Ralf K. Heilmann, , ,

| Summary:

Lynx is one of four large-mission concept studies for NASA’s 2020 Decadal
survey. The design reference mission includes an X-ray grating spectrometer
(XGS) based on critical-angle transmission (CAT) gratings. In the past we
studied different grating sizes and arrangements using traditional flat CAT
gratings with constant bar spacing. However, new technology development brings
chirped gratings in reach. Using chirped gratings where the grating bar spacing
varies over a grating allows us to fill the aperture with larger gratings
because the chirp can compensate for some aberrations caused by the deviation
of large flat gratings from the Rowland torus. This reduces the area blocked by
grating support structures. Using larger gratings also carries potential cost
savings. We use ray-tracing to study an XGS design with chirped grating and
find that using chirped gratings of $80 * 160$ mm size allows us to reduce the
number of gratings from a few thousand to a few hundred, while simultaneously
increasing the effective area by 25% and keeping the resolving power constant.
Bending those gratings to maintain a constant blaze angle over the entire
grating increases the effective area by another 5-10%.

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