Simultaneous Measurement of Electron Beam Size and Divergence with an Undulator

We present the simultaneous measurement of beam divergence and source size based on the APS diagnostic undulator line. A 300-μm-thick Si(400) crystal monochromator is used to measure the divergence with a resolution down to 3 μrad (1 μrad with the third harmonic). X-rays transmitted through the crystal are simultaneously used by a pinhole camera to measure the beam size, at a resolution of about 40 μm. We demonstrate that this measurement of emittance is robust against fluctuations of lattice functions due to a partial cancellation of systematic errors present in each of the measurements.