Low-energy spherical grating monochromator, resolution and flux comparison with normal incidence monochromator

A low-energy (7–40 eV) modified spherical-grating monochromator (SGM) layout is presented. The expected resolution and photon flux for this low-energy SGM beamline on the storage ring ASTRID are compared with an existing Normal Incidence Monochromator (NIM), namely the 5 m McPherson at the SRS in Daresbury (UK). The low-energy SGM has about a factor of 21–57 higher flux for a 0.02% bandwidth and also a better ultimate resolution. The much higher flux results from the large horizontal acceptance (40 mrad) possible at a low-energy storage ring and the expected efficiency of the grazing-incidence grating.