The monochromator consists of benders (for sagittal focusing), tilt stages (for diffraction angle adjustments), and several travel stages (for aligning monochromator crystals). Key components of the monochromator are shown in Figures 1a & b.
Heat load on the upstream crystal is reduced by filters (various thicknesses of aluminum and graphite) and a cooling scheme that uses liquid nitrogen-cooled helium (< -180°C). In the fall of 2013, the monochromator was successfully commissioned. Its performance parameters (flux, energy range, ΔE/E) were characterized and noted below. As a comparison, at A2, flux at 30 keV using a set of roughened Si(111) Bragg crystals is 1×1011 ph/s in a 1 mm2 spot that is not focused in either direction. A plot of measured flux in the hutch is shown in Figure 2. Intensity profile of 40 keV beam in the hutch is shown in Figure 3. This upgrade project was led by a CHESS research associate, Peter Ko.
Flux at 40 keV
|200 mA e+, 24-pole wiggler
Sagitally-bent double Laue Si(111)
38 to 88 keV
2×10-3 at 40 keV
|Beam FWHM, with 5mm (horizontal) ×
1mm (vertical) beam incident
on the monochromator
|1.2 mm (horizontal – focused)
1.5 mm (vertical – not focused)