Micro-focus rotating anode or liquid metal anode X-ray generators equipped with pixel array, CMOS integrating detectors, CCD camera or image plate detector are typically used as in-house X-ray source for protein crystallography.
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Micro-focus liquid anode or rotating anode X-ray generators can be endowed with stations adapted either to crystal screening or data collection:
Especially in case of membrane proteins for crystal screening the X-ray power has to meet highest demands. The liquid anode X-ray source offers a highly focused and brilliant beam, with a several times higher intensity of radiation compared to standard microfocus rotating anodes, ideal for small crystals and in-situ screening. Big wheel rotating anode X-ray generators allow a power at the focal spot of twice the brilliance than generators with normal sized anodes. Use of multilayer optics can help to further increase the flux at the crystal. These optics can be constructed with high acceptance angles for the incident radiation on the cost of a high beam divergence. As a consequence, reflections of longer lattice constants can not be properly resolved. Such a station is therefore optimized for crystal screening and less well suited for data collection.
On the other hand, optics with smaller acceptance angles and long focal distance result in a much smaller divergence of the emitted X-ray beam. Even reflections of membrane protein crystals which often exhibit very large lattice constants do not overlap with such an optic. This station is therefore much better adapted to data collection.
The flux of rotating anode generators is sometimes not powerful enough to avoid synchrotron trips for crystals screening and even the brilliance of the liquid metal anode generator offering conditions comparable to bending magnet beamlines of synchrotrons is not sufficient for the most demanding samples and experiments. Still both kinds of stations are necessary for an in-house X-ray lab of high standard. Modern pixel array counting detectors and CMOS integrating detectors provide single photon sensitivity to X-rays and low background noise compared to previous generations of detectors and enable very efficient use of in-house sources. Some in-house setups offer a combination of precise kappa goniometry with a motorized plate holder for in-situ screening and with the high brilliance liquid anode X-ray source.