High‐resolution angular beam stability monitoring at a nanofocusing beamline

Two semi‐transparent imaging beam‐position monitors developed at the ESRF have been installed at the micro‐analysis beamline ID22 for monitoring the angular stability of the X‐ray beam. This system allows low‐frequency (10 Hz) angular beam stability measurements at a submicroradian range. It is demonstrated that the incoming macro‐beam angular fluctuations are one of the major sources of focal spot instabilities downstream of the Kirkpatrick–Baez mirrors. It is also shown that scanning the energy by rotating the so‐called fixed‐exit monochromator induces some unexpected angular beam shifts that are, to a large extent, deterministic.