Soft x‐ray spectroscopy beam line on the NSLS X1 undulator: Optical design and first performance tests

The layout and first data on the performance of the soft x‐ray undulator beam line on the x‐ray ring at Brookhaven are described. The undulator (X1) has 35 periods of 8 cm, resulting in a tuning range for the fundamental of about 200–700 eV at the nominal ring energy of 2.5 GeV. The monochromator is based on the Dragon concept with spherical grating, movable exit slit but with water‐cooled optical elements in order to deal with the maximum flux of ca. 400 W. This system represents one of the next generation of soft x‐ray undulator beam lines which will figure prominently at new synchrotron radiation facilities such as ALS, ELETTRA and BESSY II. During the first performance tests absorption spectra of simple molecules at the C, N, and O K edges have been recorded with resolution and flux so far unattained in the soft x‐ray region.