Design and characterization of an undulator beamline optimized for small-angle coherent X-ray scattering at the Advanced Photon Source

An undulator beamline and small-angle-scattering spectrometer have been imp lemented at the Advanced Photon Source. The beamline is optimized for perfo rming small-angle wide-bandpass coherent X-ray scattering measurements, and has been characterized by measuring static X-ray speckle patterns from iso tropically disordered samples. Statistical analyses of the speckle patterns have been performed from which the speckle widths and contrast are extract ed versus wavevector transfer and sample thickness. The measured speckle wi dths and contrast are compared with an approximation to the intensity corre lation function and found to be in good agreement with its predictions.