Scientific goals
The scientific goal of BL18U1 is to achieve beam spot of high brightness and photon flux to micrometer level, which can be used to effectively determine the crystal structure of proteins with crystal size as small as 5-10 microns.
Techniques and methods
The common crystallographic experimental methods such as MR, MIR, SAD, MAD and SIRAS can be carried out in BL18U1 endstation.
Raster's strategy has been implemented in BL18U1 endstation for locating very small crystals, which is very useful for data collection of microcrystals.
Raster is a method that takes advantage of X-ray to detect crystals. It is not straightforward to distinguish the diffraction between small crystals or ice-wrapped crystals if the diffraction is rather weak.
In Raster experiment, certain grid interval is defined on the Loop surface, and then frames are collected at different grid intervals. Users shall inspect the diffraction frames to locate the microcystal, and then further proceed with sample centering and data collection.
Beamline Layout
The overall layout of BL18U1 beamline at SSRF/NCPSS is depicted as follows,
Beamline specification
The detailed design goals and testing results are shown in the following figure,
| | Design goals | Testing results |
| Photon energy range(keV) | 5~18 | 5~18 |
| Energy resolution (DE/E) | 2×10-4 | 1.8×10-4 |
| Focused beam size (H×V) (mm2) | 10×7 | 9.82×4.96 |
| Photon flux at sample (phs/s@300mA) | 5.0×1011 | 5.81×1011 |
| Focused beam divergence (H×V) (mrad2) | 0.70×0.25 | 0.27×0.17 |
Endstation
| Source type | Undulator, U25 |
| Mirrors | Toroidal/Cylindrical mirror |
| Monochromator | LN2-cooled DCM with Si(111) crystals |
| Goniometer | Arinax MD2 diffractometer |
| Cryo capability | LN2 Oxford 800 Cryosystem |
| Sample mounting | Rigaku Actor Sample Changer |
| Detector type | CMOS hybrid pixel |
| Detector model | Pilatus3 6M |
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