Beamline Description

The radiation source is based on two APPLE-II elliptical undulators that are used alternatively in order to optimize the flux.

The photon dispersion system is based on a VASGM dispersion system (Variable Angle Spherical Grating Monochromator) and it includes four different interchangeable spherical gratings. The first three gratings allow resolving powers of 20000-6000, 20000-6000 and 15000-5000 in the energy ranges 35-200 eV, 200-500 eV and 500-1600 eV respectively. In addition, a fourth grating operates in the 300-1600 eV range providing higher flux with reduced resolving power (10000-2000), suitable for x-ray emission experiments Three separate branches, following the monochromator, allow setting three independent experimental chambers.

The flux in the experimental chamber, measured with the high resolution gratings for linearly polarized light at the best achievable resolution, ranges between 1.2·10¹² photons/s at 125 eV and 6·10¹⁰ photons/s between 900 eV and 1250 eV.  A gain of nearly one order of magnitude is obtained for the high brilliance grating, in accordance with theoretical predictions. Flux beyond 4·10¹¹ photons/s was measured over nearly the complete energy range covered by this high brilliance grating. The results from polarization measurements confirm a polarization above 99.7% for both, linearly and circularly polarized mode at low energies. Circular dichroism experiments indicate a circular polarization beyond 90% at the Fe L₂/L₃ edge near 720 eV.