The F2 station provides tunable doubly-focused monochromatic X-rays, originating as half of the fan of radiation from the 24-pole 1.2 Tesla CHESS East wiggler (the other half feeds F1). A white-beam collimating mirror located upstream of the F1 and F2 monochromators reduces the heat load on the optics as well as aiding in focusing and providing better energy resolution. The F2 monochromator consists of a pair of vertically-diffracting Si(111) crystals, with the second crystal providing sagittal focusing in the horizontal direction (~2 mrad of beam are focused into ~3.5 mm). The useful energy range is about 7-16 keV (1.77 to 0.77 Å). The monochromated beam is offset 2.5 cm downward from the white beam position. Vertical and horizontal beam sizes can be adjusted using a pair of water cooled slit systems located in front of the monochromator, about 20.6 m from the wiggler. A vertical focusing mirror made of rhodium-coated silicon, with a critical angle constant of 67 keV-mrad, is located 3.3 meters upstream from the beryllium entrance window to the F2 hutch, which is 25.4 meters from the source. The mirror can deflect the monochromated beam upwards from 0-25 mrad without being obscured by the Be window holder. The center of the hutch is 27.2 meters from the source and 6.5 meters from the monochromator.
F2, like A1 and F1, is fully equipped for macromolecular crystallography (see MacCHESS site for more details). Additional equipment is provided to carry out energy scans of crystals and reference samples. This station is suitable for performing MAD (multi-wavelength anomalous diffraction) and SAD (single-wavelength anomalous diffraction) experiments using elements with edges in the range 7-16 keV.
Besides crystallography, F2 may also be used to collect SAXS (small-angle X-ray scattering) data from solutions of macromolecules. The necessary equipment for SAXS is maintained by MacCHESS, and reconfiguration from crystallography to SAXS, or vice versa, can be accomplished in a few hours.
View into F2 hutch. Beam enters from right, detector is at the left. Crystal rotation stage is just left of center, fluorescence detector for crystal scans just right of center, mounted crystal between them. Cryostream and crystal-viewing camera are at top right. Beam stop is mounted on the yellow tape in the center.
|F2 Station Summary|
|Source:||e+s, 24 pole wiggler, 1.7 mrad|
|Source size:||FWHM (horizontal) = 3.76 mm, FWHM (vertical) = 0.944 mm|
|Distance to source:||27.2 m to center of hutch|
|Carbon filters:||0, 1, 2.5, 5, 10, 15, 25 mm (optional)|
|Cave slit sizes:||0 to 50 mm (horizontal), 0 to 12 mm (vertical)|
|Flux:||8x1011 doubly-focused into 3.6 mm x 0.32 mm|
|Monochromators:||Double-bounce downward, offset 25.4 mm|
|Crystals||Sag. Focus.||Energy (keV)||λ||λ/2||λ/3|
|Si (111)||Yes||7-16 (1.7-0.77 Å)||1.3||0.008||0.093|
|Rh coated Si||24 inch||Yes||67.0|
|Float Glass||9 inch||No||30.6|
|Type||Energy Range||Equipment Setup|
|MAD / SAD||7-16 keV (1.77-0.77 Å)||MacCHESS Oscillation equipment|
|SAXS||~10 keV (1.24 Å)||MacCHESS SAXS equipment|