A review on the High-Dynamic Double-Crystal Monochromator for Sirius/LNLS

Abstract

The High-Dynamic Double-Crystal Monochromator (HD-DCM) started to be developed in 2015 by the Brazilian Synchrotron Light Laboratory (LNLS) for the 4th-generation light source Sirius. The reason for the unique and innovative control-based architecture was twofold, namely: 1) reaching the unprecedented target of 10 nrad RMS (root mean square) (1 Hz - 2.5 kHz) in crystals parallelism for a vertical-deflection DCM, to comply with the smaller new-generation source sizes; and 2) unlocking the potential of high-stability fixed-exit continuous energy scans, creating unmatching spectroscopy capabilities that benefit from the higher new beam brightness. The outcome is a machine built on essential high-precision mechatronics principles, with an integrated design for optimized dynamics, actuation, metrology, and thermal aspects. The first two units are operational at the MANACA (protein crystallography) and the EMA (extreme conditions and spectroscopy) undulator beamlines. This work reviews the key aspects of this new technology and presents experimental commissioning results at the beamlines, including high-quality energy continuous fly-scans up to 500 eV/s over 1 keV that demonstrate the good performance for X-ray spectroscopy by keeping inter-crystals stability below 15 nrad RMS up to 10 kHz. Preliminary EXAFS data collected at the EMA beamline at 1 keV/s is also shown. Furthermore, a discussion is held about the required beamline integration level, since the high-end experiments demand appropriate control strategies, data acquisition, triggering and performance capabilities, particularly concerning the source, the sample environment, and the detectors.