On evaluating x-ray imaging crystals with synchrotron radiation

Bent crystals used in diagnostics of plasmas combine x-rays diffracted from across the crystal. Therefore imperfections in the resulting 1-D spectrum or 2-D image are not the best way to find out why one particular crystal may differ in its performance from another and what, if anything, to do about it. Instead, here we want to measure the diffraction locally, with the necessary resolution. Nominally monochromatic and unidirectional radiation from the synchrotron's standard x-ray optics proved to be insufficient for the purpose. Here much better radiation comes from the x-ray topography setup at the x-ray optics testing beamline 1-BM at the Advanced Photon Source, thanks to a specially designed quartz conditioning crystal. Some worrisome features in a bent crystal's diffraction have thereby disappeared, while minor fabrication flaws remain highly visible.