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-/spl mu/m-thick Si(400) crystal monochromator is used to measure the divergence with a resolution down to 3 /spl mu/rad (1 /spl mu/rad 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 /spl mu/m. 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.