First results from a macromolecular crystallography system with a polycapillary collimating optic and a microfocus X-ray generator

The design and performance of a high-flux X-ray crystallography system, optimized for diffraction measurements from small macromolecular crystals, is described. This system combines a microfocus X-ray generator [40 µm full width at half-maximum (FWHM) spot size at a power level of 40 W] and a short focal length (F = 2.6 mm) polycapillary collimating optic, and produces a small-diameter quasi-parallel X-ray beam. Measurements of the X-ray flux, divergence and spectral purity of the resulting X-ray beam are presented. The X-ray flux through an aperture of 250 µm diameter produced by the microfocus system is 16 times higher than that from a 3.15 kW rotating-anode generator equipped with a pyrolytic graphite monochromator. Diffraction data from lysozyme test crystals collected with the microfocus X-ray system are of high quality and can be reduced with standard crystallographic software, yielding an overall merging factor R_sym ≤ 6%. Significant additional improvements in flux are possible, and plans for achieving these goals are discussed.