SuperESCA beamline description

The monochromator of the SuperESCA beamline is a modification of the standard version of the plane grating SX700 monochromator.
The new design, represented in the figure, has been developed in order to make the SX700 work stigmatically: the vertically-oriented cylindrical pre-focusing mirror sagittally focuses the radiation into the monochromator's horizontal entrance slit. Inside the monochromator the light is directed towards the plane grating (1200 l/mm) by a plane mirror with variable angle of incidence.

The dispersed radiation is finally focused into the exit slit by an ellipsoidal mirror, oriented vertically in order to reduce the slope error problem arising from its aspherical shape. The exit slit aperture can be varied from 5 to 100 um, giving the possibility to find the optimum compromise between energy resolution and flux for each kind of experiment.
The number of elements between the slits is the same as in the original scheme of the SX700, and the performance is mainly determined by the quality of the ellipsoidal mirror. The energy resolution can be further improved by acting on the baffles placed along the optical path inside the monochromator in order to reduce stray light; the monochromator resolving power (E/ΔE) is of the order of 10⁴.