Design of a Beam Size Monitor Using Fresnel Zone Plates

Measuring electron-beam sizes is very important to estimate horizontal and vertical emittances in lowemittance rings. The beam size monitor using Fresnel zone plates (FZPs) has been designed for the Super-SOR ring (a new name of the VSX ring), which is a thirdgeneration synchrotron light source being planned by the University of Tokyo. The monitor system has a structure of a long-distance x-ray microscope using two FZPs and has an advantage of direct and real-time monitoring of the electron beam profile. The synchrotron radiation from the electron beam at a bending magnet is monochromatized by a double-crystal monochromator and the electron beam profile is magnified and imaged on an x-ray CCD camera by two FZPs. The spatial resolution is estimated to be about 1 μm for the photon energy of 5 keV and it is sufficiently high to measure the horizontal and vertical beam sizes, 14 μm and 3.6 μm at minimum, respectively. The design of the new beam profile monitor using Fresnel zone plates is presented in this paper.