Measurement of ultralow vertical emittance using a calibrated vertical undulator

Abstract

Very few experimental techniques are useful for the direct observation of ultralow vertical emittance in electron storage rings. In this work, quantitative measurements of ultralow (pm rad) electron beam vertical emittance using a vertical undulator are presented. An undulator radiation model was developed using the measured magnetic field of the APPLE-II type undulator. Using calibrated experimental apparatus, a geometric vertical emittance of ϵ_{y}=0.9±0.3 pm rad has been observed. These measurements could also inform modeling of the angular distribution of undulator radiation at high harmonics, for proposed diffraction-limited storage ring light sources.