The maximum power density on the monochromator is about 20 W/mm2. A cryogenically cooled Si-111 channel-cut monochromator withstands this power load without severe broadening of the rocking curve. A closed liquid-nitrogen loop provides automatic operation of the cooling system. To reduce background radiation from the storage ring, the beam is vertically displaced by 30 mm. The Si(111) crystal can select energies between λ = 0.155 nm and λ = 0.073 nm. At λ = 0.1 nm (12.4 keV) the bandwidth is of the order of ΔE/E =2.10-4.


An uncooled horizontally reflecting toroidal mirror follows the monochromator. The mirror has a fixed shape and can only be used with wavelengths longer than 0.073 nm. In both directions the maximum reflection angles are 12 mrad. Because of the small beam-divergence the focusing parameters can be kept fixed for all experiments. The mirror characteristics were chosen to minimise the beam size at the detector position. The following figure shows the calculated beam size along the 30 detector tube.



Beam characteristics

optical elements: double monochromator toroidal (or cylindrical) mirror
distance from source: 29.6 m 34 m
type: Si(111), cryogenically cooled
30 mm vert. displacement
Rh coated
beam size at sample posit.: unfocused focused
(at 55 m , 12.5 keV
HxV, FWHM) in mm2 :
(real mirror)
2.6 x 1.3
0.4 x 0.2 (0.45 x 0.06)


spectral range : 8- 17 keV (0.073 - 0.15 nm)
resolution in Δ E/E : 2.0 10-4 at 12.5 keV



Further Information