Performances and first experimental results of BACH, the beamline for dichroism and scattering experiments at ELETTRA

Abstract

BACH, the new soft x‐ray beamline for polarization dependent experiments at the Italian synchrotron radiation facility ELETTRA, has been commissioned, characterized and opened to external users. Based on two APPLE II undulators, it covers an energy range between 35 eV and 1600 eV with the control of the light polarization. The monochromator works either in high resolution or high flux mode. Resolving powers of 16000 at 50 eV, 12000 at 90 eV, more than 12000 at 400 eV, 15000 at 534 eV and 6600 at 867 eV have been achieved with the three high resolution gratings. The resolving powers of the high flux grating, which covers the 290 – 1600 eV range, have been measured reaching 7000 at 400 eV and 2200 at 867 eV. The fluxes, in the high resolution mode, range between 4⋅1011 photons/s at 125 eV and 2⋅1010 photons/s at about 1100 eV. Using the high flux grating with the best resolution achievable 1.7⋅1011 photons/s impinge on the sample at 900 eV. Two branches are installed after the monochromator allowing the set‐up of two different experimental stations. One of them, besides several facilities for surface preparation and analysis, hosts a compact inelastic soft x‐ray spectrometer (ComIXS) dedicated to x‐ray emission experiments exploiting the small spot (10 μm in the vertical direction) on the sample. The other branch hosts a liquid helium cryostat equipped with a superconducting coil to perform absorption and transmission experiments with temperatures down to 2 K and magnetic field up to ±7 T.