For the second mirror a state-of-the-art toroidal mirror has been chosen, in order to achieve an achromatic character on the optics. The role of this mirror in the optical scheme is crucial, as the focusing action (meridional and sagittal) is exclusively performed on this element. The mirror is 1.2 m long x 140 mm wide with a fix  toroid radii and variable curvature radius in the meridional direction. It is covered by a Pt coating and the surface is facing down. As a toroid, two radii define this mirror: the minor (also called sagital) radius is fixed at 60 mm; the major (or meridional) radius is specified from 5 to 40 Km, meaning focalizing. The figures of merit of the surface quality includes a slope error of 0.3 mrad and a roughness of 0.2 nm, as resumed following table.

 

B1

B2

B3

Position from the source

45.8 m

51.8 m

59 m

Experimental hutch

1

2

2

M2 incident angle

3.89 mrad

2.72 mrad

2.136 mrad

Energy cut-off

21.7 keV

31 keV

39.5 keV

Meridional curvature radius

5 Km

11.7 Km

21.6 Km

Beam dimension (H x V)

40 x 30 mm

35 x 50 mm

45 x 70 mm

Beam absolute height

1410.7 mm

1427.5 mm

1461.6 mm

Table. Resume of the operating conditions of the second mirror for the different focal points. The beam absolute height is increased by 15 mm when using the post-monochromator.