Toroidal mirror mask

The toroidal mirror mask (TMM) serves as a horizontally-limiting aperture in the beamline upstream of the two toroidal mirrors M1i and M1o, at distance of 15.63 m from the undulator. It intercepts most of the x-ray beam, which is horizontally wide and vertically narrow at this location. As the TMM is moved up in $y$ by the TMM motor, the open part of the aperture of width $w$ appears to shift in the outboard direction $x$ according to the relationship

$$w=y\cos\theta=x\sin\theta$$

For the existing slit (see Fig. 3.6), $w=5$ mm and $\theta=78^{\circ}$ so that the apparent horizontal width of the slit is 5.11 mm, and a vertical motion of $y=10$ mm corresponds to a horizontal motion of $x=2.13$ mm. The vertical height of the slot is 43.6 mm (the motor can go from -60,000 to +60,000 microns, but that includes the distance to put the wide slot into the beam path), corresponding to a total sideways aperture range of 9.3 mm.

Figure 3.6: The toroidal mirror mask (TMM). The photograph at left shows the water-cooled plate on which the mask is mounted, and the mask itself as an inset. The approximate dimensions of the mask installed in December 2004 is shown at right.