Performance of the Compact Visual Beam Imaging System on the GM/CA BM Beamline at the APS

Abstract

A typical problem encountered on a beamline with a sagittal focusing monochromator is the difficulty of optimizing the crystal alignment because the full width of the monochromatic, unfocused beam cannot be visualized. This problem is particularly acute on beamlines that accept a wide swath of radiation combined with a fixed experimental setup consisting of constrained apertures that only allow the focused beam to pass through to the sample position. To address this problem, an imaging system has been designed and implemented on the GM/CA bending magnet beamline at the Advanced Photon Source, Argonne National Laboratory. This imaging system consists of a 30mm × 50mm flat YAG crystal, right angle prism/mirror and video camera located downstream of the vertical collimating mirror, sagittally focusing monochromator and vertical focusing mirror. The YAG crystal was installed in a 6-way vacuum cross in the beam path, and was mounted on a linear translation feedthrough allowing remote controlled insertion and removal of the crystal from the beam path. The CCD camera was mounted outside the vacuum chamber and views the x-ray induced scintillation from the YAG crystal through a window. This visualizer allows one to optimize the twist, yaw and roll of the second crystal, facilitates proper sagittal focusing and serves as a remote controlled diagnostic tool. An overview of the design and the performance of the imaging system will be presented.