Diffraction pattern recorded during ptychographic scans using the Siemens star test sample. The large overall size of the signal on the detector indicates that even the smallest features of the sample contribute to the signal and can thus be reconstructed. Interference fringes (the separation between the intensity maxima and intensity minima) can clearly be seen, showing that CoSAXS indeed offers a coherent beam to its users. Credit: Maik Kahnt
A successful, first rigorous test of CoSAXS, the Small-Angle X-ray Scattering beamline at MAX IV has now completed. A collaboration of scientists from NanoMAX, Balder, and CoSAXS beamlines demonstrated the accuracy, capabilities, and most especially, coherence properties of the instrument. The work marks the first experimental measurements for coherence in a SAXS beamline at a fourth generation synchrotron.
The high brilliance and excellent coherence of the X-ray beam played a vital role in the success of the measurements. The testing for CoSAXS, which began in November 2020, was inspired by earlier, similar measurements taken at imaging beamline, NanoMAX. Digital investigation preceding and during the experiment made for smooth progress.
“The optics at CoSAXS have been extensively simulated by our MAX IV colleague Konstantin Klementiev. It was natural to compare experimental results against these measurements,” said Maik Kahnt, MAX IV beamline scientist. “We could also verify that these simulations are correct. This allows to use these simulations to calculate the coherence properties for other sets of parameters and beamline settings, and to trust them.”
The tests ran in three stages. The first part measured and verified the beamline optics with tele ptychography, where the beam size and shape were compared against theoretical data. In the next stage, scientists analysed the instrument setup with parameters matching the simulations. The beam was first adjusted to a smaller diameter using an additional pinhole, then tested for settings to deliver optimal coherence and those settings outside a desirable range. Lastly, the performance of the instrument was assessed with an X-ray Photon Correlation Spectroscopy (XPCS) experiment on colloidal particles. The SAXS detector operated at the highest possible frame rate or most extreme conditions and produced quantitative coherent scattering data.
Beyond the test results, the message from CoSAXS beamline team is coherently clear. Apply now for beamtime. MAX IV’s new high-performance, multi-purpose SAXS instrument works!
Experimental setup inside the experimental hutch of the CoSAXS beamline: The X-ray beam (from left to right) passes through a pinhole (in the black, drop-shaped holder) before it hits the sample (held from the bottom) and then enters through the window into a 15m long flight tube. Credit: Maik Kahnt
Kahnt, M., Klementiev, K., Haghighat, V., Weninger, C., Plivelic, T. S., Terry, A. E. & Bjorling, A. Measurement of the coherent beam properties at the CoSAXS beamline (2021). J. Synchrotron Rad. 28.