A1 and
F1 each receive about 1 milliradian of radiation emitted from the West and East
24-pole wigglers, respectively. Each beam is intercepted by a cylindrically-bent silicon
crystal and simultaneously diffracted and focussed in the horizontal plane. An optional
channel-cut crystal can be used to increase the monochromaticity to 2 eV energy resolution
for MAD experiments. The beam is then focussed vertically by a cylindrically bent
rhodium-coated silicon mirror. The focal spot size at the specimen for 13 keV photons is
approximately 2 mm horizontal by 0.4 mm vertical.
The x-ray optical system for the A1 and F1 experimental stations:
Because of the enormous heat flux produced by the wiggler, the cooling of a first optical element is of primary importance to delivering a high flux beam to the experiment. If the primary monochromating crystal is to be tunable, the radius of curvature must be variable. The challenge, then, is to design a cooling device that can accommodate a changing crystal bend radius.
This was accomplished by a copper block in the shape of an elongated "C" that is machined flat. The triangular crystal is attached only at its base. As a differential screw spreads the two ears of the C-shaped copper block, the copper surface is curved, thereby bending the crystal. Since the copper block only holds the base of the crystal and pushes at its tip, the triangular shape of the crystal guarantees a nearly perfect cylindrical figure. This shape provides the best focussing of x-rays. The added benefit of the current design is that as the copper block bends into an approximate cylinder, its close proximity to the crystal facilitates cooling for any radius of bend.
2008 Run
Nov 19th - Dec 22nd
