BM29 white beam attenuators

There are three axes of white beam attenuators on BM29 located just after primary slits and mask: wba1, wba2 and wba3 (wba1 upstrem). Motors have 2450 steps/mm with backlah 25 steps for wba1 and 100 steps for wba2 and wba3. There is 2000 steps per motor turn and distance between filters is 33.76 mm. Hysteresis of home is 0.2 mm. Filters foil locations from down to top (i.e. translation moving down):

• wba1 (upstream): empty (when translation completely up), 0.5mm Al, 1 mm Al, 2 mm Al;
• wba2: empty, 0.05 mm Mo, 0.1 mm Mo; 0.25 mm Mo;
• wba3: empty, 0.025 mm Cu, 0.05 mm Cu, 0.1 mm Cu.

Usually no white beam attenuators are used. Idea was to have a possibility to protect DML (double multilayer) monochromator from low energies. Axes with filters can be easily moved using Filtergui appli running on nela (icon on right display).

BM29 monochromatic attenuators

Monocromatic attenuators are mounted in their vacuum vesssel "hérisson" located in the Optics hutch just after the Be-window as far as possible from sample position to avoid/diminush any parasitic scattering from them. Schematic drawing of a stacable modul with 2 filters is shown on the left. We used 4 such modules having 8 pneumatic actuators with Aluminium foils of different thicknesses. They are atomatically introduced to the beam if less than 100% transmission (= full beam) required, for example in the case of radiation damage taking into account the absorption of different Al foils for a given energy.

Thicknesses of Al foils going downstream: 50 microns, 100 microns, 150 microns, 150 microns, 1 mm, 500 microns, 1 mm and 1 mm.