Very small beam-size measurement by a reflective synchrotron radiation interferometer

A synchrotron radiation (SR) interferometer with Herschelian reflective optics has been developed for the measurement of beams of several μm in size. In a conventional refractive SR interferometer, the dispersion effect of the objective lens limits the instrument to a smaller range of beam-size measurements. To avoid this problem, we designed a Herschelian arrangement of reflective optics for the interferometer. The effectiveness of the reflective SR interferometer was confirmed at the KEK Accelerator Test Facility (ATF) damping ring. The measured vertical beam size obtained using the reflective SR interferometer was 4.7μm and the estimated vertical emittance was 0.97×10−11m .