Monochromator

Update

The optical part of ID09 is now equipped with a new cryogenically cooled Si(111) monochromator:

view of the cryo-cooled channel-cut monochromator(68 kB)

More news soon, meanwhile take a look at the previous setup:

General Description

The ID09 beamline has a water-cooled monochromator designed to operate between 5 -39 keV. The water-cooling can extract 25 W before the rocking curve starts to broaden. It is mainly used with the U20 undulator and occasionally with the U46 and W70 at low currents, i.e. single-bunch mode.

The distance between the two crystals is held fixed at Dt= 10.0 mm, and that causes a vertical shift in the position of the beam with Bragg angle. In energy scans the height of the experimental table is linked to the energy of the monochromator such that fixed-exit scans can be realised. The crystals are mounted in a holder that has a weak mechanical link that allows adjusting the angle between the crystals. The crystal holder is fixed onto a rotation table, which is driven from outside the vacuum. The horizontal beam position is controlled at two levels: a stepper motor tilts the first crystal and a piezo tilts the second with high resolution.
The rejection of harmonics has to be considered due to the fixed energy cut-off at 38 keV of the toroidal mirror. In the range 4.5-12.7 keV, the (333) reflection contaminates the beam. The problem can be solved by opening the gap of the undulator hereby the content of hard radiation is reduced.

The energy resolution is determined by the Si(111) rocking width and is found to be about 3 eV. It can be tuned by a slight tilt of the second crystal to 2 eV.