Construction and performance of beamline NE1B for circularly polarized soft x rays in the TRISTAN accumulation ring

Beamline BL-NE1B has been constructed at the 6.5-GeV TRISTAN accumulation ring (AR) for applications of circular polarization in the soft x-ray region. Circularly polarized soft x rays are produced by a helical undulator operation mode of an insertion device, EMPW♯NE1. The fundamental harmonic peak can be tuned from 0.25 to 2 keV. The NE1B beamline is equipped with a vertical-dispersion spherical-grating monochromator using the Rowland mounting. A monochromatized circularly polarized photon flux higher than ∼1011 photons/s has been obtained over an energy range from 0.25 to 1.25 keV with an energy resolution (E/ΔE) of around 1500–300. An energy resolution of about 5000 has been achieved at 400 eV with slit widths of 10 and 10 μm.