Improvement of Fresnel zone plate beam-profile monitor and application to ultralow emittance beam profile measurements

We describe the improvements of a Fresnel zone plate (FZP) beam-profile monitor, which is being developed at the KEK-ATF damping ring to measure ultralow emittance electron-beam profiles. This monitor, which is designed to have a submicrometer spatial resolution, is based on x-ray imaging optics composed of two FZPs. Various improvements were performed to the old setup. First, a new crystal monochromator was introduced to suppress the beam image drift. Second, the two FZP folders were improved in order to realize a precise beam-based alignment during x-ray imaging. Third, a fast mechanical shutter was installed to achieve a shorter time resolution, and an x-ray mask system was also installed to obstruct direct synchrotron radiation through the FZPs. These improvements could make beam-profile measurements more precise and reliable. The beam profiles with less than 50   μm horizontal beam size and less than 6   μm vertical beam size could be measured within a 1 ms time duration. Furthermore, measurements of the damping time and the coupling dependence of the ATF damping ring were successfully carried out with this upgraded FZP monitor.