In-vacuum X-ray helical undulator for high flux beamline at SPring-8

An in-vacuum X-ray helical undulator has been developed for a high flux beamline (BL40XU) of SPring-8. Since BL40XU is not equipped with a monochromator in order to provide high photon flux, on-axis fundamental radiation from the helical undulator is directly used for user experiments after being focused by horizontal and vertical mirrors. The energy resolution available at the beamline is determined by the undulator spectrum and the front end physical aperture. Compared to a conventional beamline of SPring-8 with a crystal monochromator, the available photon flux is higher by two orders. Since a specific polarization state is not requested from the user experiments, there is no phasing mechanics on the undulator. The magnet structure is newly designed to obtain better magnetic field performance. The measured spectral bandwidth shows a good agreement with the expected one.