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In the summer of 2013, a new double-Laue monochromator for high-energy X-rays was installed in the F-cave. 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 Figure 1.

Fig 1, Top

Fig 1, Bottom

Figure 1: Top: key components of the F2 double-Laue monochromator; bottom: sagittal bender. Red arrows indicate paths of X-ray travel

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.

Source 
Monochromator 
Source-to-monochromator 
Monochromator-to-hutch 
Energy range 
Flux at 40 keV 
ΔE/E 
200 mA e+, 24-pole wiggler
Sagitally-bent double Laue Si(111) 
20.75 m 
6.69 m 
38 to 88 keV 
5×1012 ph/s
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)

 

Figure 2

Figure 2: Plot of measured flux from 40 to 80 keV

Figure 3

Figure 3: 40 keV beam intensity profile in the hutch

 

 

Submitted by: Peter Ko, CHESS, Cornell University
01/29/2014