The M2 mirror, positioned at 18.8 m from the source point is a 2:1 demagnifying primary focusing mirror with a cylindrically shaped fixed sagittal radius that focuses the beam in the horizontal with the pitch determining the optimal horizontal focus at the focal plane (ES1 in the hutch). The bending of the long mirror axis is dynamical and can be adjusted to optimize the vertical focus. This bend, while adjustable, is set in the metrology according to the exact dimensions of the source and focus spot and left constant as much as reasonably possible.
As thatthe main adjustable for the primary focus is the pitch of the mirror since it brings the both horizontal and vertical spot size in focus at the same plane (provided the bends are set correctly).
In practice, the pitch (and if needed the bends) are optimized at the start of an operation cycle and then defined through slits set around the resulting focus position in the plane perpendicular to the X-ray beam. The slits thus define a virtual secondary source that can be either directly utilized for experiments (end station 1) or refocused by a set of KB mirrors onto end station. Through this, the optimized primary focus can easily be recreated by maximizing the X-ray flux through the virtual source slits by moving the beam vertical (changing the pitch of M2) and horizontal (changing the roll of the second crystal of the monochromator theta2, Chi2). This is automatized and can be done by users. Instructions are here.
The M2 mirror is coated with 4 nm of rhodium coating over 25 nm platinum over a 5 nm chromium ‘glue’ layer
