May 4, 2009

Beamline News: X6A Undergoes Major Upgrade

Last November, in less than a week, a major upgrade of the area detector and goniostat was implemented at the National Institutes of General Medical Sciences (NIGMS)/NSLS end station X6A. This rather short amount of work time can be attributed to proper design and careful preparation in concert with the providers of both the detector (Area Detector Systems Corporation (ADSC), Poway, CA) and the goniostat (XTAL LOGIC, Los Angeles, CA), which precisely orients and positions the crystal. In this short time, all equipment in the hutch was removed, the hutch was "sanitized," and the new upgraded equipment was installed, aligned, and tested (Figure 1). The equipment includes an optical table, a goniostat, a detector, a cryosystem and an automounter. This team work was performed by Vivian Stojanoff, Jean Jakoncic, Kun Qian, Rick Greene (NSLS); Charles Strousse (Xtal Logic); and Chris Nielson and Ron Hamlin (ADSC). The new detector is three times more efficient than any charge coupled device-based detector from the competition and much larger than the previous detector. Due to a high dynamic range and a high efficiency, diffraction data can be recorded at higher resolution with the same exposure time.

The X6A end station before the upgrade.

The X6A end station after the upgrade.

The new goniostat is composed by an air-bearing rotary stage that is 40 times faster, 10 times more accurate and more stable than the previous one and allows fully automated crystal centering. The high-magnification camera combined with a high-quality mirror allows us to center crystals as small as 20 microns, and data can be collected on a micro crystal at a bending magnet beamline.

Other important improvements are the helium path that, depending on the energy, increases the flux at the sample by a factor of up to two and dramatically reduces air scattering that contributes to background noise. Finally, the new pair of slits allows beamline scientists to achieve a tight focus between the sample and the detector, further improving the data quality. Together, these improvements allow a higher beamline efficiency. Users are exposing their samples to the x-ray beam three times less than what they were doing before. Furthermore, we are routinely operating with a small beam size, up to 75 microns with no beamline stability issues. We are already working on the design of an automated beamstop, an automated in-helium beam-position monitor and, more importantly, additional focusing optics (crossed pair of kinoform lenses or Kirkpatrick-Baez mirrors) that will allow us to focus the beam even more. We hope to install this equipment by the end of 2010. The final beamline should deliver copious and stable beam with a flux density gain of more than 50. The faster the data comes, the faster we should be able to analyze it. Therefore, we upgraded all computing capabilities at the beamline. We also quadrupled the data storage and processing power to allow users to leave the beamline not only with the diffraction data but, most of the time, with an electron density map and, often, with a partially refined model.

ARTICLE BY: Jean Jakoncic