## 5 ST-CXI System and Example Observations  
Figure 4 shows a schematic view and photograph of the implemented imaging system [32]. The system mainly consists of an STXI and its positioning tables, a sample holder and its positioning tables, a phase shifter and its positioning tables, an asymmetric crystal and its positioning table, an image feedback system, and an X-ray imager. Beamline BL-14C of the Photon Factory was dedicated to the imaging system. Vertical fan-shaped white SR emitted from the vertical wiggler of the beamline is first monochromatized by a double crystal monochromator using Si (220) diffraction (not shown in Figure 4) and introduced to the imaging system. The beam size of monochromatic SR is 70 mm in the vertical direction but only a few mm in the horizontal direction, so an asymmetric crystal is installed upstream of the STXI to expand the width of the beam by several times using asymmetric XRD. Although this enlargement reduces the SR intensity, uniform SR with a several-10-mm-width is generated for fine observation. One of the interference beams generated by the STXI is used for PCXI, while the other is used by the feedback system. The positioning table for the STXI consists of three tables to increase mechanical rigidity during operation: (1) Table S1 for adjusting the STXI relative to the incident X-rays to satisfy the Bragg diffraction condition, (2) Table S2 for tuning the \(\theta\) rotation between the crystal blocks, and (3) a tilt table for tuning the tilt rotation between the crystal blocks. Table S2, which requires 10-prad positioning control accuracy for fine imaging, has a sleeve bearing to attain high mechanical rigidity (mechanical resonance frequency of 300 Hz or higher) and a fine adjustment mechanism driven by a laminated piezoelectric actuator (PZT) with 10-picometer positioning precision. Extremely high rotational stability of 10 grad between crystal blocks can be achieved by avoiding deformation of the table caused by gravity and cutting floor mechanical vibration, so a horizontally rotating table is suitable. \begin{table}
\begin{tabular}{c c c c} \hline
**No** & **Field of View** & **Imaging Capability** & **R\&D Target** \\ \hline
1 & 25 \(\times\) 15 mm & Interference pattern & Configuration and driving system of positional \\  & & & tables for prod rotational accuracy [33] \\
2 & 30 \(\times\) 30 mm & Phase map & Feedback system to suppress drift rotation and sample positioner [34] \\
3 & 40 \(\times\) 60 mm & Phase-contrast CT & Image feedback system and sample manipulation for CT [29] \\ \hline \end{tabular}
\end{table} 
Table 2: Prototypes in development of ST-CXI imaging system. Figure 4: Schematic view (**left**) and photo (**right**) of ST-CXI system at beamline BL-14C of Photon Factory of KEK in Japan. With this table configuration, X-rays are diffracted horizontally, so a large field of view can only be attained by using the world's only vertical fan, SR, at BL-14 of the Photon Factory. Since CT measurement takes more than one hour even using high-intensity SR, an image feedback system is needed to suppress the drift rotation of Table S2 within 10 prads for a few hours. The rotation of S2 causes fringe motion in the X-ray interference pattern, so the feedback system compares the position of the current interference fringes with that obtained beforehand and adjusts the voltage applied to the PZT to keep the fringe position the same. The latest feedback system can suppress phase drift within \(\pi\)/50 rad (5 prads in terms of the angle \(d\theta\) of Table S2) for more than 6 h [32]. The time constant of this feedback is 1 s, so this system suppresses the drift due to thermal fluctuations, etc. over a long period of time. Furthermore, the fast mechanical vibrations of less than 1 s are reduced by the high mechanical rigidity of the positioning tables, as mentioned above. In addition, an active vibration-isolation mechanism to cut floor vibration and a double acrylic cover to reduce the effect of surrounding sound are installed.