Mini-beam modes on standard MX beamline BL17U at SSRF.

The macromolecular crystallography beamlines at third-generation synchrotron facilities play a central role in solving macromolecular crystal structures and also in understanding the biological function at molecular levels. The MX beamline BL17U at Shanghai Synchrotron Radiation Facility is a typical standard MX beamline with a focused beam size (H × V) of FWHM around 80 μm × 45 μm. However the protein samples brought to the beamline are down to 5-10 m from the important and challenging science project now. These samples require smaller size beam. In order to achieve the mini-size beamline, two mini-beam modes have been developed on BL17U: the pinhole-based mini-beam and the focused mini-beam by compound refractive lens (CRL). Compared to the pinhole-based mode, three times increase in flux is obtained by the CRL mode at a similar beam size. The flux gain obtained by the CRL needs to be considered for data collection strategies. It takes few minutes to switch the beamline from the normal to CRL mini-beam mode.