Beamline& Endstation
Beamline
XTM beamline located at BL1.2W between the other two beamlines (BL1.1W: MXT and BL1.3W: SAXS), takes the center of the fan beam radiation generated from the 2.2-Tesla multipole wiggler for the high photon intensity to benefit x-ray imaging. The XTM beamline is composed of 2 key optical elements: 1) Focusing mirror (FM); and 2) Double crystal monochromator (DCM). The x-ray beam is focused with a toroidal mirror located 8900 mm from the radiation source. Then, the x-ray beam is transferred to the DCM with a pair of Ge 111 crystals located at 33000 mm downstream. Between the focusing mirror and the DCM, there is the x-ray attenuator that opts a set of filters to attenuate low energy x-ray photon from the spectrum.
The XTM beamline can be operated in 2 modes: 1) polychromatic x-ray beam mode, and 2) monochromatic x-ray beam mode. In polychromatic x-ray beam mode (referred to as White beam mode), the x-ray beam will bypass the DCM bringing the most of x-ray photons of the spectrum for absorption-contrast x-ray imaging. Although it is useful for rapid data acquisition, the heat-associated radiation damage of the sample should be concerned. Typically, the x-ray attenuator is applied to remove low-energy x-rays from the beam spectrum, which would otherwise not contribute to image quality but would add to radiation dose. In monochromatic x-ray beam mode, the x-ray beam will be diffracted by a pair of Ge(111) crystals giving monochromatic x-ray beam of 5 – 18 keV with 0.1% bandwidth. This has enabled the elemental specific imaging allowing for quantitative analysis such as K-edge subtraction. With the available energy, the monochromatic beam mode should be benefit for organic samples or polymer samples. Currently, the development for monochromatic x-ray beam mode at the XTM beamline is in progress.
Endstation
The experimental station is designed based on microtomography geometry. When the x-ray beam exits the transferring tube, it will project at the rotating sample and the x-ray images will be acquired by the detection system as presented in the picture. The movement of the sample is governed with a 6-axis goniometer from which the sample can be rotated and translated along X-, Y-, and Z-axis. On top of the goniometer is equipped with a goniometer head that is carried the sample. It can be translated in X- and Y-axis with a short traveling range of ± 5 mm allowing for centering the sample to the rotation axis. The detection system is located after the sample to acquire the x-ray images. This is composed of a YAG-Ce scintillator, the lens-coupled microscope (Optique Peter, France), and PCO.edge 5.5 scientific CMOS camera (chipset 2560 x 2160 pixels). The detector system can be moved in Y-axis to optimize the sample-to-detector distance from 0 – 100 cm via the sliding guide. Featuring two observing cameras, the experiment can be monitored from outside the enclosure.
The operation of XTM beamline and experimental station is regulated by Safety Section following the radioprotection principle, ALARA (As low as reasonably achieved). The XTM beamline operation is governed by the interlock safety system as to prevent the user from radiation exposure.
Optical performance
The optical performance of XTM beamline is primarily relied on the objective lens-coupled microscope and the chipset of PCO.edge 5.5 camera. The field of view (FOV) and expected pixel size contributed by the available objective lens including 2X, 5X, 10X and 20X are listed in the table.
