The GSECARS bending magnet branch 13BM receives 6 mrad of horizontal beam fan. A mask close to the shield wall blocks a central 1mrad section dividing the fan into two separate beams for experimental stations 13BM-D and 13BM-C. In the optics hutch 13BM-A the outboard part of the incident fan is monochromated by a Si 111/311 double crystal monochromator with adjustable crystal offset. In the 13BM-B station this beam is focused by 1m long KB mirror and directed to the experimental station 13BM-D. The inboard beam for the 13BM-C station is first bounced down by a vertical focusing mirror, also located in 13BM-B. To maximize spatial separation of the two beams the inboard part of the fan is deflected by a single-bounce Rowland circle monochromator (shown schematically on the left). Because of the single-bounce design, the setup operates at fixed energy, since changes of the 13BM-C monochromator angle change the beam path in the experimental station.

The 13BM-C monochromator holds two different crystals optimized for different fixed energies (15 keV and 28.6 keV). For diamond anvil cell experiments the experimental station operates at constant energy of 28.6 keV. The Rowland circle monochromator utilizes an asymmetrically cut and dynamically bent crystal which focuses the beam in the horizontal direction. Beam focusing in the vertical direction (and removal of higher order harmonic contamination) is achieved with a use of the dynamically bent vertical focusing mirror. In horizontal plane the beam is pre-focused by the monochromator, and then fine-focused by a second stage Kirkpatrick-Baez mirror (currently 600 mm length, with Pt coating). The current focused beam size on the sample at 29 keV is approximately 0.012(H) x 0.018(V) mm.

The experimental station 13BM-C is equipped with a unique heavy duty high-precision Newport 6-circle kappa diffractometer (4 circles for sample rotation + 2 circles for detector rotation), shown on the right. The Newport diffractometer can be used with a wide range of X-ray detectors, including Pilatus 1M/100K photon counting detectors and MAR165 CCD detector, and is compatible with all currently used types of diamond anvil cells.

The Newport diffractometer with its high speed (up to 15 deg/sec) high load capacity (up to 25 lb), high precision of rotation (sphere of confusion below 10 micrometers) and exceptional number degrees of freedom available for sample and detector manipulation is ideal for advanced crystallography experiments.

Future Plans

• Multigrain analysis (powders treated as single crystals)
• 3d pair distribution function (single crystals with defects)
• Electron density distribution modeling (electron orbital shape and bonding density determination)
• Thermal Diffuse Scattering (TDS) analysis for elastic properties determination