2020同步年報

Facility Status 111 3-GeV electron beam. The measured energy distribution of the irradiation centers at E p = 7.376 keV and 4.998 keV, with a common energy spread of ~0.7% (full width at half maximum, FWHM). The consistent results indicate a satis- factory alignment of the central magnetic field (maximum ~0.86 T at gap 6.8 mm) of IU24 to the 3-GeV electron-beam trajectory. The corresponding flux profiles measured at the sample position demonstrate the expected high flux, above 2 × 10 14 photons/s in 7−12 keV with DMM, and a wide X-ray energy range 4−23 keV with DCM, at e-beam current 400 mA of the 3-GeV storage ring. The calculated evolutions of beam size and divergence are outlined in Fig. 2(c) . The beam sizes ( Fig. 2(d) ) after the sample position were measured with the Eiger X 9M detector moving along the vacuum vessel of length 12 m and diameter 1.5 m. The vertical beam size decreases to the focusing design target ~50 µm at 50 m (10 m from the sample position), whereas the horizontal beam size decreases to target size 180 µm at an earlier position, 45 m. The slowly varying beam size over beam path 10 m originates from the designed small de- magnification ratio ~1.5 of the KB focusing mirrors, which is advantageous for SAXS with a wide range of sample- detector distance. In the USAXS mode operation, the horizontally collimating 4BCC manifests its unique function in significantly suppress- ing the horizontal parasite scattering, especially near the direct beam of the critical USAXS low- q region. As shown in Fig. 3(a) , although the main (DCM) beam intensity 8 keV is decreased about 10 fold by the 4BCC, the overall S/N ratio can be improved more than 10 fold, because of the highly suppressed parasite scattering by more than 100 fold. The corresponding beam size 8 keV (FWHM) at SD distance 9.47 m decreases from 160 to 110 µm (FWHM) when the 4BCC is moved into the beam path for collimation, whereas the ver- tical beam size maintains ca. 70 µm. Inset in Fig. 3(b) shows the USAXS images measured for a standard nanopattern, revealing a well resolved 1 st lamellar peak at q = 0.00063 Å -1 under a detecting limit of minimum q ca. 0.0004 Å -1 , with a Tatum beamstop (4.0 mm dia.). For the microbeam oper- ation with the microslits opened to 10 µm in both V and H directions, the microbeam KB mirrors could focus the beam to the sample position for beam dimensions 26 µm (H) by 10 µm (V) measured, as shown in Figs. 3(c) and 3(d) . The beam sizes were measured using the two diamond X-ray beam position monitors of Rigi and Civi-2 situated at 37 and 40 m, respectively. Fig. 3 : (a) Measured horizontal and vertical beam dimensions at a sample-detector distance of 9.47 m, with a DCM 8-keV beam, with and without 4BCC in the X-ray beam path. The horizontal beam size (FWFM) decreased from 160 to 110 µm, and the vertical beam size maintains ca. 70 µm. Note that the background intensity in (a) near the main beam decreased by two orders of magnitude. (b) USAXS profile extracted from the 2D patterns (inset up, with a left room-in image) of a standard nanopattern (inset, down), measured using a 6-keV beam of DCM further collimated with the 4BCC, resolving a lamellar spacing of 1000 nm with the 1 st lamellar peak at q = 0.00063 Å -1 and a minimum detectable q at 0.0004 Å -1 . (c) and (d) are the measured vertical and horizontal beam dimensions of a 15-keV microbeam with the DCM; the corresponding microslits have opening 20 µm in both vertical and horizontal directions. Note that the microbeam was slightly off-focused at 37 m (5 µm, FWHM) before the targeted sample position at 40 m (12 µm, FWHM).