Design and performance of the soft X-ray energy materials research beamline at SSRF

Abstract:  A soft X-ray energy materials research beamline (BL20U2), a branch of energy materials beamline (E-line), has been constructed in the Shanghai Synchrotron Radiation Facility (SSRF) Phase-II project. It is now operational for soft X-ray resonant emission spectroscopy (RXES) and soft X-ray resonant elastic scattering (REXS) investigations. Optical optimization was implemented for high performance, e.g., photon flux, energy-resolving power, and focus spot size. RXES experiments show that the energy range extends from 150 to 1500eV. The elastic peak measured near titanium absorption edge (445eV) indicates an energy resolution of the RXES spectrometer of 65meV. The measured photon flux is 3 × 1012 photons/s at 244eV at the RXES sample position for an SSRF electron energy of 3.5GeV and a projected ring current as 300mA. The spot size at the RXES sample position is 23um in the horizontal direction and 7.9um in the vertical direction, respectively. Moreover, the angular resolution of elastic REXS scatterometer reaches 0.005 degree through measurement of X-ray  reflection from the single crystal silicon wafers. A sample of the REXS scatterometer is vibrationally decoupled from its chamber and cooled using copper braids connected from an open cycle liquid helium cryo reservoir, whereas the minimum sample temperature is below 15K.