Development of undulator photon beam monitor at the photoemission beamline in the Siam Photon Laboratory

Abstract This report presents the visualization and characterization of soft X-ray undulator radiation at 120 eV for the photoemission spectroscopy and microscopy beamline (BL3.2U PES/PEEM) at the Siam Photon Laboratory. The undulator radiation is monochromatized using a multilayer mirror at the front end of the beamline. The multilayer film, deposited on a silicon substrate, is designed to diffract the 120 eV undulator radiation at an incidence and reflection angle of 45°. The multilayer is attached to the photon beam absorber shutter (ABS), which is controlled by a pneumatic mechanism, allowing for the inspection of the undulator harmonic pattern whenever the ABS is closed. The vertically diffracted undulator radiation from the multilayer is converted to visible light through a scintillator and monitored using a CCD camera through a quartz viewport outside the vacuum. Using red shifted undulator harmonic radiation, a distortion in the photon beam profile is observed. This report details the development of the soft X-ray undulator photon beam imaging system, commissioning results, issues studied related to electron beam orbit deviation, and magnetic field simulations to reproduce the deformed image.