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

摘要:  Asoft 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 opera
tional 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 po
sition for an SSRF electron energy of 3.5GeV and a projected ring current as 300mA. The spot size at the
 RXES sample position is 23µm in the horizontal direction and 7.9µm in the vertical direction, respectively.
 Moreover, the angular resolution of elastic REXS scatterometer reaches 0.005◦ 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.