Beamline Description
The monochromator
The grazing incidence channel is a based on a monochromator working in parallel light with variable deviation angle. The grazing channel is composed by a plane mirror and two plane laminar gratings G1200 and G1800, respectively with 1200 and 1800 ll/mm. The mirror collects the plane radiation from the first paraboloidal mirror. The monochromator works in the internal first order configuration. The PMGM optical layout allows to deliver the same wavelength following different Deviation Angles (the Deviation Angle is the angle between the incident and the reflected beam from the mirror), for the optimization of the flux or for higher order rejection. The first curve optimizes the experimental flux on the sample, the second one is the curve that gives the maximum flux, assuming that the calculated ratio given by the higher orders and the first order is less than 1%. According to the PMGM scheme, the plane mirror rotates around an axis far from the centre of the mirror and at different positions of the mirror the deviated ray doesn’t reach the same position on the grating surface. This fact suggests not to use the mirror rotation for energy scansion, but it’s better to place M1 in the optimal position and only rotate gratings. The two gratings rotate around an axis placed in the centre of its optical surface. The plane laminar grating G1200 works in the energy range 40–1400 eV, while G1800 is for the energy range 600 – 1400 eV.
The grazing incidence channel
The normal incidence channel
The normal incidence channel works in the 2.7–50 eV spectral range. The channel is composed by a plane mirror and a plane grating GNIM with 1200 ll/mm. The normal incidence channel works also in parallel light but at fixed deviation angle of 30° (that is, the radiation illuminates the plane mirror M2 with an incidence angle equal to 15°). Then, differently from the grazing incidence, this channel has only one degree of freedom, that is the rotation of the grating around the centre of its surface. The grating is optimised to work at 40 eV with the incidence angle of 16.10°.
