Energy-resolved beam-monitoring system for undulator radiation using scattering from a chemical-vapor-deposition diamond film.

With low-emittance synchrotron radiation rings, introducing accurate x-ray beams to a sample is difficult, and ensuring that the direction of the undulator beam is stable is essential. However, measuring the centroid of the undulator photon beam at the beamline front-end (FE) is difficult because the soft x-ray radiation is contaminated by the bending magnets upstream and downstream of the undulator. The x-ray beam position monitors (XBPMs), based on the interaction with the halo of undulator radiation, cannot estimate the centroid of the beam, and they cannot eliminate the effects of the bending magnets. To solve this problem, we have developed an energy-resolved beam-monitoring system for undulator radiation with the scattering from a diamond thin film deposited by chemical vapor deposition (CVD) in this study. An undulator x-ray beam is irradiated onto this film, and its elastic and Compton scattering are observed through a 50 μm-diameter pinhole. A beam spot is detected through a pinhole camera system using a direct-detection-type charge-coupled device camera with energy resolution. The peak of the first-order harmonic of the undulator radiation is selectively visualized to measure the centroid of the undulator radiation, as well as the spectrum. The proposed system using a CVD diamond film can provide accurate position information for a photon beam exiting the FE.