The experimental set-up

Contact: richard.bean@xfel.eu

 

The SPB/SFX instrument is primarily concerned with 3D structure determination of both crystalline and non-crystalline micrometre-scale and smaller ob­jects. A particular emphasis is placed on biological objects, including viruses, biomolecules and protein crystals. Nevertheless, the instrument is also capable of investigating non-biological samples using similar techniques. The instrument exploits the unique high repetition rate of the facility and brings benefit to these structural biology applications [1].

The SPB/SFX instrument is designed to operate at photon energies from 3 to 16 keV, with peak perfor­mance expected between about 6 and 15 keV. The SPB/SFX instrument is located behind the SASE1 undulator, with X-ray beam delivered via a dedicated branch in the XTD9 photon tunnel. The SPB/SFX in­strument has two interaction regions where sample interactions with X-rays and laser sources are meas­ured, one termed Interaction Region Upstream (IRU) and the other termed Interaction Region Downstream (IRD) [1]. The general layout of the SPB/SFX instru­ment is shown in Fig. 1. The X-rays propagate from the source to their focal point at IRU entirely through a vacuum, arriving with a full width at half-maximum (fwhm) focused diameter of a few micrometres or a few hundred nanometres using either of two Kirkpat­rick–Baez mirror systems [2]. A set of compound re­fractive lens refocusing optics (providing a microme­ter-sized focus) are installed after IRU to enable measurements at IRD in an air/helium or vacuum en­vironment [2].

 

Schematic of SPB/SFX instrument layout.

 

The SPB/SFX instrument deploys three main classes of sample delivery: liquid jets for delivering (primarily) small crystals to the X-ray FEL beam for serial crys­tallography, focused aerosol beams for delivering (primarily) non-crystalline particles to the X-ray FEL beam for single particle imaging, and samples arranged on fixed targets, which may be crystalline or non-crystalline. The IRU at SPB/ SFX uses the Adaptive Gain Integrating Pixel Detector (AGIPD) [4], a hybrid pixel array, silicon sensor-based detector for collecting the forward diffraction and scattering data.

 

Illustration of X-ray path and diffracted X-ray beam from a water jet onto the AGIPD detector.

 

The experiment to study crystallization of water was performed at IRU of the SPB/SFX instrument. The sample for this experiment, water, was delivered to the interaction region using a liquid jet delivery sys­tem [5] with some slight modifications. The X-rays were focused to about 100’s of nm at IRU using the nano KB focusing system to achieve the very high fluence required for resolving the structural infor­mation. By controlling the distance of the nozzle for the liquid jet to the interaction point, the water to ice transition region was probed using X-ray diffraction. The diffraction data was collected using the AGIPD detector with up to 1.1 MHz repetition rate. The inter­action of water/ice with X-rays was also imaged using the pump-probe laser [6].

 

[1] Wiedorn, M.O., et al. Megahertz serial crystallography. Nat Commun 9, 4025 (2018)
[2] Mancuso, et al. J. Synchrotron Rad. 26, 660-676 (2019)
[3] Bean, et al. J. Opt. 18, 074011 (2016).
[4] Allahgholi, et al. J. Synchrotron Rad. 26, 74-82 (2019)
[5] Schulz, et al. J. Synchrotron Rad. 26, 339-345 (2019)
[6] Koliyadu, et al. J. Synchrotron Rad. 29, 1273-1283 (2022)

 

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